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Transcript of IEJ.01.2009
Effectiveness of ozone againstendodontopathogenic microorganisms in a rootcanal biofilm model
K. C. Huth1, M. Quirling1,2, S. Maier1, K. Kamereck3, M. AlKhayer1, E. Paschos4, U. Welsch5,T. Miethke3, K. Brand6 & R. Hickel1
1Department of Restorative Dentistry & Periodontology, Ludwig-Maximilians University, Munich; 2Institute of Clinical Chemistry &
Pathobiochemistry, Klinikum rechts der Isar, Technische Universitat Munchen, Munich; 3Institute of Medical Microbiology,
Immunology and Hygiene, Technische Universitat Munchen, Munich; Departments of 4Orthodontics and 5Anatomy, Ludwig-
Maximilians University, Munich; and 6Institute of Clinical Chemistry, Medizinische Hochschule Hannover, Hannover, Germany
Abstract
Huth KC, Quirling M, Maier S, Kamereck K, AlKhayer M,
Paschos E, Welsch U, Miethke T, Brand K, Hickel R.
Effectiveness of ozone against endodontopathogenic microor-
ganisms in a root canal biofilm model. International Endodontic
Journal, 42, 3–13, 2009.
Aim To assess the antimicrobial efficacy of aqueous
(1.25–20 lg mL)1) and gaseous ozone (1–53 g m)3)
as an alternative antiseptic against endodontic patho-
gens in suspension and a biofilm model.
Methodology Enterococcus faecalis, Candida albicans,
Peptostreptococcus micros and Pseudomonas aeruginosa
were grown in planctonic culture or in mono-species
biofilms in root canals for 3 weeks. Cultures were
exposed to ozone, sodium hypochlorite (NaOCl; 5.25%,
2.25%), chlorhexidine digluconate (CHX; 2%), hydro-
gen peroxide (H2O2; 3%) and phosphate buffered saline
(control) for 1 min and the remaining colony forming
units counted. Ozone gas was applied to the biofilms in
two experimental settings, resembling canal areas
either difficult (setting 1) or easy (setting 2) to reach.
Time-course experiments up to 10 min were included.
To compare the tested samples, data were analysed by
one-way anova.
Results Concentrations of gaseous ozone down to
1 g m)3 almost and aqueous ozone down to 5 lg mL)1
completely eliminated the suspended microorganisms
as did NaOCl and CHX. Hydrogen peroxide and lower
aqueous ozone concentrations were less effective.
Aqueous and gaseous ozone were dose- and
strain-dependently effective against the biofilm
microorganisms. Total elimination was achieved by
high-concentrated ozone gas (setting 2) and by NaOCl
after 1 min or a lower gas concentration (4 g m)3)
after at least 2.5 min. High-concentrated aqueous
ozone (20 lg mL)1) and CHX almost completely
eliminated the biofilm cells, whilst H2O2 was less
effective.
Conclusion High-concentrated gaseous and aqueous
ozone was dose-, strain- and time-dependently effective
against the tested microorganisms in suspension and
the biofilm test model.
Keywords: antimicrobials, biofilm, endodontics,
microbiology, ozone, root canal.
Received 18 April 2007; accepted 1 July 2008
Introduction
The successful treatment of an infected root canal,
especially those with persistent apical periodontitis
remains a clinical challenge (Nair 2006). The main
aim of endodontic treatment is to eradicate or substan-
tially reduce the microbial load in the root canal
Correspondence: Dr Karin Christine Huth, Department
of Restorative Dentistry, Periodontology & Pedodontics,
Dental School, Ludwig-Maximilians University, Goethestr.
70, 80336 Munich, Germany (Tel.: +49 89 5160 9411;
fax: +49 89 5160 9302;
e-mail: [email protected]).
doi:10.1111/j.1365-2591.2008.01460.x
ª 2008 International Endodontic Journal International Endodontic Journal 42, 3–13, 2009 3
system, which is conventionally achieved by chemo-
mechanical instrumentation followed by canal filling to
prevent recolonization (Nair 2006). Endodontic irri-
gants must have effective antimicrobial activity but
also exhibit relatively no cytotoxicity toward periapical
and oral mucosal tissue. An anti-inflammatory action
especially in cases of persistent apical periodontitis
might also be advantageous.
Enterococcus faecalis and Candida albicans have been
reported to be of particular interest in cases of persistent
periodontitis (Molander et al. 1998, Sundqvist et al.
1998, Siqueira & Rocas 2004, Fouad et al. 2005).
Anaerobic bacteria, such as Peptostreptococcus micros or
Gram-negative bacteria including P. species have also
been associated with persistent infections (Siqueira
2002). These microorganisms grow in highly resistant
biofilms (Pinheiro et al. 2003), but also as planctonic
cells suspended in the fluid phase of the root canal or as
remnants after mechanical canal preparation (Distel
et al. 2002, Nair 2006).
Sodium hypochlorite (up to 5.25%) is the most
commonly used root canal irrigant and has been used
alternately with H2O2 (3%) (Takeda et al. 1999).
Chlorhexidine digluconate (2%) has also been recom-
mended for root canal irrigation in combination with
mechanical debridement (Siqueira et al. 1998, Gomes
et al. 2001, Basrani & Lemonie 2005). However, the
success rate for conventional treatment of persistent
and refractory apical periodontitis is only in the order of
between 50% and 70% (Weiger et al. 2001) and
consequently NaOCl up to 3% has been reported to
have limited efficacy against high-pathogenic endo-
dontic microorganisms and CHX 2% has demonstrated
inconsistent results (Siqueira et al. 1998, Gomes et al.
2001). In addition, side effects such as haemorrhage,
oedema and skin ulceration have been reported when
high concentrations of NaOCl and H2O2 come into
contact with oral tissues (Pashley et al. 1985, Oncag
et al. 2003, Gernhardt et al. 2004). A significant degree
of cytotoxicity towards oral cells has been found in vitro
as well (Hyslop et al. 1988, Nagayoshi et al. 2004,
Huth et al. 2006). Chlorhexidine (2%) may cause
mucosal desquamation, impaired wound healing and
tooth staining (Bassetti & Kallenberger 1980, Cline &
Layman 1992) and a high cytotoxic potential has been
demonstrated on epithelial cells (Huth et al. 2006).
Therefore, an alternative endodontic antiseptic with
high antimicrobial potential and fewer side effects
would be valuable.
Ozone is currently being discussed as a possible
alternative antiseptic agent in dentistry because of its
reported high antimicrobial power without the devel-
opment of drug resistance (Restaino et al. 1995,
Paraskeva & Graham 2002). Ozone gas in a concen-
tration of �4 g m)3 (HealOzone; KaVo, Biberach,
Germany) is already being used clinically for endo-
dontic treatment. However, results of studies into its
efficacy against endodontic pathogens has been incon-
sistent, and there is little information regarding the
most appropriate application time and concentration to
use (Nagayoshi et al. 2004, Arita et al. 2005, Bezruk-
ova et al. 2005, Hems et al. 2005). Regarding the
demand on relative non-toxicity toward periapical and
oral mucosal tissue for the endodontic irrigants (Nair
2006), the ozone gas concentration currently used in
endodontics (4 g m)3) has been shown to be slightly
less cytotoxic than NaOCl (2.5%) and aqueous ozone
(up to 20 lg mL)1) showed essentially no toxicity to
oral cells in vitro (Filippi 2001, Ebensberger et al. 2002,
Nagayoshi et al. 2004, Huth et al. 2006). The aim of
this study was to investigate the antimicrobial efficacy
of gaseous and aqueous ozone against specific endo-
dontic pathogens in suspension and in biofilms grown
in human root canals.
Materials and methods
Microorganisms
Freeze-dried microorganisms: E. faecalis (ATCC 14506;
LGC Promochem, Wesel, Germany), C. albicans (ATCC
MYA-273), P. micros (ATCC 33270) and P. aeruginosa
(ATCC 15442) were suspended in brain heart infusion
medium (BHI) and recultivated on Schaedler agar
plates (vitamin K1 and 5% sheep blood; BD Diagnostic
Systems, Heidelberg, Germany).
Test agents
Dose–response experiments were performed for gaseous
and aqueous ozone covering a concentration range as
wide as possible to evaluate if there was a concentra-
tion that could possibly compete with the established
endodontic irrigants in antimicrobial effectiveness.
Basically following a log2 scale, the concentration
ranges were limited because of the experimental setting
and equipment. Ozone gas (Ozonosan photonic,
Dr Hansler, Iffezheim, Germany) in concentrations
between 1 g m)3 (the minimum concentration to
measure by the available ozone gas measuring device)
and 53 g m)3 (the highest achievable concentration
because of the experimental set-up and the limitation
Ozone and endodontic biofilms Huth et al.
International Endodontic Journal, 42, 3–13, 2009 ª 2008 International Endodontic Journal4
of the ozone generator) was applied to the test
microorganisms in a self-constructed glass chamber
with simultaneous concentration measurement
(GM-6000-NZL; Anseros, Tubingen, Germany). The
analytical method of the concentration measuring
device is based on UV light absorption at a wavelength
of 253.7 nm where gaseous ozone has its maximum
absorbance (Bocci 2002). For aqueous ozone, bi-
distilled water was treated with ozone gas (75 lg mL)1,
15 min) using the ozone generator, which resulted in a
final photometrically confirmed (Palintest 1000 Ozone
Meter, Palintest Ltd, Gateshead, UK) ozone concentra-
tion in water of 20 lg mL)1 (saturation point), which
was diluted to 1.25 lg mL)1. The ozone concentration
measurement in water involves the oxidation of a
colourless indicator (diethyl-p-phenylene diamine) to
a pink compound by ozone in comparison with a
reference sample without ozone (manufacturer’s infor-
mation, operating wavelength of the photometer is
505 nm). Ozone was compared with freshly prepared
solutions of NaOCl (5.25%, 2.25%), CHX (2%), H2O2
(3%) and phosphate buffered saline (PBS) as a control.
As ozone is an endothermic, highly instable oxygen
compound (Sehested et al. 1991, Hoigne 1998,
Stubinger et al. 2006), both the gas and the ozonated
bi-distilled water were freshly prepared before each
experiment. During production and processing of the
ozone experiments only ozone-resistant materials were
used (e.g. ozone demand-free glass, ozone-resistant
piping material).
Testing ozone against microorganisms in suspension
Microorganisms were grown overnight (37 �C, 10 mL
of BHI), centrifuged, resuspended in PBS to a turbidity
of McFarland 1 [3 · 108 colony forming units
(CFU) mL)1] and diluted 1 : 3. Ten microlitres were
suspended in 1 mL of agent for 1 min followed by
immediate, appropriate dilution with PBS as evaluated
by preceding experiments. Thereof, 10 lL were plated
out on agar plates and incubated aerobically (48 h,
37 �C). For the obligate anaerobic P. micros, all
experimental steps were completed in an anaerobic
work bench (Bactron, Sheldon Manufacturing Inc.,
Cornelius, OR, USA; 85% N2, 5% H2, 10% CO2; 37 �C).Again, 10 lL of an equal dilution of the specific
microorganism suspension were plated out on agar
plates and exposed to ozone gas whilst the control
plates were exposed to ambient air (1 min). After
incubation of the agar plates (48 h, 37 �C), the number
of CFU mL)1 was determined.
Testing ozone against microorganisms in biofilms
grown in human root canals
Crowns of freshly extracted single rooted permanent
teeth (root length 18–19 mm), were removed at the
level of the cemento-enamel junction. The use of the
teeth for these experiments had been agreed upon by
informed consent of the patients. The root canals were
instrumented to the size ISO 40 (K-files; Dentsply
Maillefer, Ballaigues, Switzerland), the apical regions to
size 30 (ProFile�.04; Dentsply Maillefer) with intermit-
tent canal irrigation following each file size (3 mL of
NaOCl 5.25%) (Takeda et al. 1999, Zehnder et al.
2003). Finally, the canals were irrigated with EDTA
10% (5 min, 10–30 mL) followed by normal saline
(Zehnder et al. 2003), dried with paper points and the
roots sterilized (121 �C, 2 bars, 5 min).
The biofilm growth assembly (Fig. 1) contained a
programmable peristaltic pump (IPC-8; Ismatec, Wert-
heim-Mondfeld, Germany), freshly prepared autoclaved
artificial complete saliva (Pratten et al. 1998), 10%
aqueous sucrose solution (Sigma-Aldrich, Schnelldorf,
Germany), flexible silicone tubes (diameter 1 or
2.06 mm; Hartlmaier, Munich, Germany), several
flasks and the prepared dental roots. The ingredients
for the saliva were from Oxoid (Wesel, Germany),
Sigma-Aldrich and BD Diagnostic Systems. All the
equipment was sterilized before use. Overnight cultures
of E. faecalis, C. albicans or P. aeruginosa were used. The
latter species substituted the anaerobic P. micros which
could not be evaluated since the growth assembly was
too large to be incorporated into the anaerobic work
bench. The experiments with P. aeruginosa were con-
fined to the biofilm trials because of the greater
relevance than the suspension experiments already
undertaken for the other three strains.
The artificial saliva was constantly pumped through
a flexible tube into a 50-mL reservoir, supplemented
with the sucrose solution three times a day (30 min,
3 · 33 mL) (Wilson et al. 1998). For the first week, an
overnight culture (37 �C in 10 mL of BHI) of the
respective strain was added daily to the saliva. The
nutrient broth from the reservoir was pumped
(720 mL day)1) (Wilson et al. 1998) through the
canals of four parallel-mounted dental roots each
hanging in a flask, the coronal canal orifice connected
to the flexible tube by a 10-lL micropipette tip
(Eppendorf, Hamburg, Germany). To avoid a contam-
ination of the root surface, the used saliva, which
dropped from the roots’ apical region to the bottom of
the flask, was constantly pumped off into a waste flask
Huth et al. Ozone and endodontic biofilms
ª 2008 International Endodontic Journal International Endodontic Journal, 42, 3–13, 2009 5
via a wider flexible tube (diameter 2.06 mm). After
3 weeks, the roots were removed and cut into 5-mm-
thick horizontal slices, and the apical root portions
were disposed of.
For each test condition, one slice was carefully
transferred to a flask and 1 mL of the test agent added
(four independent trials). For the ozone gas exposure,
two experimental settings were used: setting 1, the
slices were laid flat on glass beads into the gas box, that
the gas streamed over the canal space (resembling
canal areas that are difficult to reach); setting 2, the
slices were positioned upright so as to allow the gas to
stream through the root canal (resembling canal parts
that are easy to reach). After 1 min, the agent was
removed or the slice was removed from the gas box,
1 mL of PBS was immediately added and the slice
vortexed for 1 min (Wilson et al. 1998). Restrained
reactions beyond the 1 min contact time could have
occurred as no chemicals were used to stop the action.
Rather, the vast majority of the test agents were
removed immediately after 1 min and PBS added for
appropriate dilution. Thereafter, 100 lL were plated
out on agar plates and incubated (48 h, 37 �C), andthe CFU per plate were counted. Additionally within
setting 2, ozone gas (4 g m)3) was applied for longer
time intervals, i.e. 2.5, 5 and 10 min. The counted
number of CFU were calculated as a percentage of the
respective control (mean ± SD; n = 3–4).
For each of the independent trials, one slice was
checked for the presence of a biofilm inside the root
canal and for possible microbial contamination of the
outer root surface by scanning electron microscopy
(JSM-35 CF; Jeol, Eching, Germany and SmartSEM;
Zeiss, Oberkochen, Germany).
Statistical methods
As a result of the large number of test agents, the
experiments were conducted in several stages each
with its own control. To compare the antimicrobial
Figure 1 Growth assembly for the mono-species biofilms in root canals. Mono-species biofilms of endodontic pathogens were
grown for 3 weeks in prepared dental root canals of extracted single-rooted permanent teeth. For this purpose, a peristaltic pump
carried pre-warmed artificial saliva supplemented with sucrose and microorganism broth from a reservoir through the roots to a
waste flask at a rate of 720 mL day)1 under aerobic conditions at 37 �C. The right part of the drawing is a magnified view of an
exemplary root hanging in a flask.
Ozone and endodontic biofilms Huth et al.
International Endodontic Journal, 42, 3–13, 2009 ª 2008 International Endodontic Journal6
activity of the agents, the counted CFU were calculated
in percentage of the respective controls (mean ± SD;
n = 3–4). For all experiments, the absolute numbers of
CFU, the percentage values and the means with
standard deviation of the independent trials are given
in the accompanying Supporting Information. Data
were analysed by one-way anova with Tamhane post
hoc tests to compare independent samples (two-tailed
tests, a-level 0.05) (spss software 12; SPSS Inc.,
Chicago, IL, USA).
Results
Effect of ozone on microorganisms in suspension
Firstly, the effect of aqueous and gaseous ozone on the
specific endodontic pathogens in planctonic culture
was evaluated (see Supporting Information, Tables
A–C). Aqueous ozone completely eliminated E. faecalis
and C. albicans when used in concentrations down to
5 lg mL)1, whereas lower concentrations (2.5 and
1.25 lg mL)1) reduced substantially but did not elim-
inate them totally (Fig. 2a,b). In the case of P. micros,
aqueous ozone down to 2.5 lg mL)1 led to complete
eradication whilst 1.25 lg mL)1 was less effective
(Fig. 2c). In comparison, NaOCl and CHX led to a total
elimination of the tested microorganisms, whereas
H2O2 reduced but did not eliminate them. Ozone gas
in concentrations down to the tested minimum of
1 g m)3 for 1 min almost completely eliminated the
tested strains with a mean reduction of more than 99%
(Fig. 2a–c, Supporting Information, Tables A–C). Sta-
tistically, no differences in effectiveness of the different
agents were seen for E. faecalis (anova, P > 0.05).
Regarding C. albicans, H2O2 and low concentrations of
ozonated water (2.5 and 1.25 lg mL)1) were signifi-
cantly less effective than all other agents (P < 0.05).
Against P. micros, low dose ozonated water
(1.25 lg mL)1) was less effective than the other
antiseptics (P < 0.05).
Establishment of the anatomical biofilm model
The experimental set-up (Fig. 1) allowed the growth of
mono-species biofilms of E. faecalis, C. albicans and P.
aeruginosa over 3 weeks in an anatomically correct form
inside the canal of tooth roots. The roots were sectioned
into horizontal slices before exposure to the gas/agents.
The formation of biofilms was checked for the different
species by SEM of one slice for each independent trial as
well as the outer root surfaces, which showed no
bacterial contamination or biofilm formation (pictures
not shown). P. aeruginosa was substituted for the
anaerobic P. micros because the growth assembly was
too large for the anaerobic chamber.
Effect of ozone on microorganisms in biofilms
The antimicrobial action of ozone against E. faecalis,
C. albicans and P. aeruginosa mono-species biofilms was
tested (see Supporting Information, Tables D–F). Appli-
cation of aqueous ozone for 1 min was dose-depen-
dently effective against the microorganisms, its highest
concentration of 20 lg mL)1 revealing mean CFU
reductions of over 96%, similar to CHX 2% (Fig. 3a–
c, Supporting Information, Tables D–F). Sodium
hypochlorite (5.25%) completely eliminated the micro-
organisms, whilst H2O2 was less effective. In this series
of experiments, ozone gas was applied to the root slices
laying flat in the gas box (setting 1), which revealed a
dose-dependent effectiveness of ozone gas against the
different species (Fig. 3a–c). E. faecalis and C. albicans
was almost eliminated by the highest gas concentration
achievable within the experimental setting (53 g m)3)
(Fig. 3a,b) and P. aeruginosa by the highest and the
second highest concentration (Fig. 3c). Statistically, no
significant differences in effectiveness could be found
between the antiseptics for E. faecalis and C. albicans
(anova, P > 0.05). Against P. aeruginosa, ozone gas
4 g m)3 was significantly less effective than NaOCl,
CHX and ozonated water down to 10 lg mL)1 and
ozonated water 10 lg mL)1 less effective than CHX 2%
(anova, P < 0.05). This was mainly because of a very
small standard deviation in comparison with lower gas
and ozone water concentrations, which showed no
significant differences.
Exposure of the biofilm to ozone gas in a different
setting and with longer contact times
In the following, the experimental conditions were
changed by positioning the slices with E. faecalis
biofilms upright with their cut surfaces in front of the
inlet of the gas box as to allow the gas to stream
through the root canal (setting 2) rather than over the
canal space as in the setting before. Two concentrations
were selected, i.e. one high gas concentration
(32 g m)3) as well as a lower concentration, which is
currently used in dentistry (4 g m)3; HealOzone).
Comparing the outcome of the two settings, the high
gas concentration led to complete eradication of viable
cells after 1 min in the new setting whilst in the old
Huth et al. Ozone and endodontic biofilms
ª 2008 International Endodontic Journal International Endodontic Journal, 42, 3–13, 2009 7
setting only a reduction was observed (Fig. 4a). Ozone
gas in the lower concentration (1 min) reduced the cell
count more than before, but not to zero. Therefore, as a
last step, the effect of longer exposure times (2.5, 5 and
10 min) of this concentration was tested on the
bacterial biofilms. Contact times of 2.5 min and more
with 4 g m)3 ozone gas led to complete elimination of
the microorganisms (Fig. 4b), but without being sig-
nificantly different to the cell count after 1 min
(P > 0.05) (see Supporting Information, Table G).
Discussion
In this study, gaseous ozone in concentrations down to
1 g m)3 substantially and aqueous ozone down to
5 lg mL)1 completely eliminated the tested planctonic
(a)
(b)
(c)
Figure 2 Antimicrobial efficacy of ozone against endodontic pathogens in suspension. The suspended microorganisms were
exposed to aqueous or gaseous ozone in different concentrations or established endodontic irrigants (NaOCl, CHX and H2O2) for
1 min. The numbers of CFU after contact with PBS for 1 min were defined as 100% control (dotted line). The remaining CFU after
agent/gas exposure were counted and calculated as a percentage of the control (n = 3–4, mean ± SD) (see Supporting
Information, Tables 1–3). (a) shows the antimicrobial activity against E. faecalis. (b) shows the antimicrobial activity against
C. albicans. (c) Shows the antimicrobial activity against P. micros.
Ozone and endodontic biofilms Huth et al.
International Endodontic Journal, 42, 3–13, 2009 ª 2008 International Endodontic Journal8
pathogens. Gaseous and aqueous ozone were dose- and
strain-dependently effective against the micro-
organisms in biofilms. Total elimination of the
microorganisms in terms of the methods used here
could be achieved by ozone gas at 32 g m)3 for 1 min
or a lower concentration (4 g m)3) for longer contact
times (‡2.5 min) in case of E. faecalis (setting 2).
Aqueous ozone in the highest concentration
(20 lg mL)1, 1 min) nearly eliminated E. faecalis,
C. albicans and P. aeruginosa biofilms.
The root canal model used in these experiments
allowed for the growth of biofilms inside the canal. To
(a)
(b)
(c)
Figure 3 Antimicrobial efficacy of ozone against endodontic pathogens associated in mono-species biofilms in a root canal model.
Mono-species biofilms were grown inside of dental root canals of extracted single-rooted teeth for 3 weeks. In the following, the
roots were cut into horizontal slices that were exposed to aqueous or gaseous ozone in different concentrations or established
endodontic irrigants (NaOCl, CHX, H2O2) or PBS as a control for 1 min. After removal and suspension of the biofilms, the
remaining number of CFU were counted and calculated in % of the CFU counts after contact with the PBS control (100%, dotted
line) (n = 4, mean ± SD) (see Supporting Information, Tables 4–6). (a) Antimicrobial efficacy against E. faecalis biofilm. (b)
Antimicrobial efficacy against C. albicans biofilm. (c) Antimicrobial efficacy against P. aeruginosa biofilm.
Huth et al. Ozone and endodontic biofilms
ª 2008 International Endodontic Journal International Endodontic Journal, 42, 3–13, 2009 9
determine the efficacy of ozone as alternative antiseptic,
it was compared with traditional endodontic irrigants
(NaOCl, CHX and H2O2) by adding the agents for
1 min. The dose–response experiments for ozone and
additionally the time-course experiments for the ozone
gas concentration currently used in dentistry (4 g m)3,
HealOzone) were aimed at finding a dose-time-concen-
tration that could completely eliminate the microor-
ganisms in the test model as a basis for clinical study
designs in the future. As a source of impreciseness in
the present study, no chemicals were used to arrest the
action of the agents. Therefore, the contact times, e.g.
for CHX, which is known for its substantivity (Khademi
et al. 2006), might be prolonged similar as in the
clinical situation.
Earlier studies reported in part contradictory results
regarding the efficacy of ozone against endodontic
pathogens: one group tested ozonated water
(4 lg mL)1, 10 min) against E. faecalis incubated on
dentine blocks for 6 days (Nagayoshi et al. 2004). A
significant reduction was found but complete elimina-
tion was not observed as was the case with NaOCl
2.5%, which is consistent with the present results.
Additionally, the trials reported here revealed that the
highest concentration of ozonated water (20 lg mL)1)
led to a near eradication of the microorganisms in the
3-week-old biofilm and a complete elimination by
gaseous ozone at a concentration of 32 g m)3 for
1 min or a lower concentration (4 g m)3) for contact
times of at least 2.5 min (setting 2). Further, the biofilm
experiments revealed a near eradication of E. faecalis by
CHX 2% whereas H2O2 was less efficient throughout.
Another study found no significant reduction of
E. faecalis biofilms (grown on membranes for 48 h)
using ozonated water, but did so against planctonic
bacteria (Hems et al. 2005). A reason for these differing
(a)
(b)
Figure 4 Antimicrobial efficacy of ozone gas applied in two experimental settings to E. faecalis biofilms and the effect of prolonged
exposure times. The biofilms were grown as described in Fig. 3. In setting 1, the horizontal root slices were laid flat on glass beads
in the gas box (see experiments in Fig. 3). In setting 2, the horizontal root slices were positioned upright with their cut surfaces in
front of the gas inlet as to allow the gas streaming through the canals. (a) The antimicrobial effect of gaseous ozone in
concentrations of 32 g m)3 and 4 g m)3 for 1 min on the E. faecalis biofilms according to setting 1 (grey bars) and 2 (black bars) is
shown in comparison. PBS served as control. The remaining CFU were counted and calculated in % of the PBS control which was
defined as 100% (dotted line) (n = 3, mean ± SD). (b) The antimicrobial effect of ozone gas (4 g m)3) according to setting 2 for
1 min and prolonged contact times (2.5 min, 5 min and 10 min) is depicted (see Supporting Information, Table 7).
Ozone and endodontic biofilms Huth et al.
International Endodontic Journal, 42, 3–13, 2009 ª 2008 International Endodontic Journal10
results compared with the study mentioned above
(Nagayoshi et al. 2004) and the present experiments
revealing a CFU reduction when exposed to high
concentrated ozonated water might be that a rather
low ozone concentration was used in the other study
(Hems et al. 2005). That is, ozone gas was bubbled
through the water containing the biofilm for only
4 min. The maximum concentration of ozonated water
(20 lg mL)1) was achieved in the present study only
after 15 min of ozonation (data not shown). Another
recent study grew E. faecalis biofilms over 60 days in
root canals and applied ozonated water, ozone gas,
NaOCl 2.5% or CHX 2% for 20 min (Estrela et al.
2007). Contrasting to the present results, none of the
irrigants were found to have an antimicrobial effect.
The effect of ozone against C. albicans has been
reported primarily for denture cleaning (Murakami
et al. 1996, Oizumi et al. 1998). More recently,
C. albicans incubated on resin plates for 120 min was
almost eliminated by use of ozonated water (2 and
4 lg mL)1, 1 min) with or without ultrasonication
(Arita et al. 2005). As 120 min represents a short time
interval for biofilm formation, that study might be
better compared with the present suspension experi-
ments, in which a mean reduction of about 86% of
C. albicans by 2.5 lg mL)1 ozonated water and a total
elimination by 5 lg mL)1 ozonated water and a
reduction of over 99% by ozone gas down to 1 g m)3
was achieved. In the present biofilm experiments,
C. albicans was found to be completely eliminated only
by NaOCl (5.25%) and to over 96% by 53 g m)3
gaseous ozone (setting 1), 20 lg mL)1 ozonated water
and CHX 2%.
The effect of ozone against the anaerobe P. micros
has not been evaluated before. Ozone gas in the tested
minimum concentration (1 g m)3, setting 1) and
aqueous ozone (‡ 2.5 lg mL)1) completely eliminated
the suspended microorganisms. Biofilm experiments
were not performed with P. micros as the growth
assembly could not be maintained in anaerobic condi-
tions.
The use of ozone as a disinfectant against
P. aeruginosa in dental unit water lines has been
reported, but there is no information about the required
time and concentration for total elimination (Filippi
1995, Al Shorman et al. 2003). In present biofilm
experiments, total eradication was achieved by ozone
gas concentrations of 32 g m)3 (setting 1) and NaOCl
(2.25%, 1 min). High-concentrated aqueous ozone
(20 lg mL)1, 1 min) and CHX 2% almost eliminated
the viable microorganisms.
Conclusions
High-concentrated gaseous and aqueous ozone was
dose-, strain- and time-dependently effective against
the tested microorganisms in suspension and the biofilm
test model. However, NaOCl was the only method that
completely eliminated all types of microorganisms.
Acknowledgements
The authors wish to acknowledge E. Thielke and
C. Kohler for technical project support. The study was
financed by the Medical Faculty, University of Munich
(FoFoLe Reg. Nr. 401), departmental funding and the
KaVo Company.
Supporting information
Additional supporting information may be found in the
online version of this article:
Table S1 Antimicrobial efficacy of ozone and estab-
lished endodontic irrigants (1 min) against the tested
microorganisms in suspension or associated in biofilms.
The absolute number of remaining colony forming units
(CFU abs) of 3 to 4 independent trials (n = 3–4) are
given. The CFU are also given in % of the respective
controls in parentheses and their means with the
standard deviations of the independent trials (% control,
mean ± SD) which correspond to Fig. 2, 3 and 4. NaOCl,
sodium hypochlorite; CHX, chlorhexidine digluconate;
H2O2, hydrogen peroxide; O3, ozone. The antimicrobial
effects against E. faecalis (A), C. albicans (B), and P. micros
(C) in suspension are shown as well as against E. faecalis
(D), C. albicans (E) and P. aeruginosa (F) associated in
biofilms. Table G shows the antimicrobial efficacy of
ozone gas in concentrations of 32 g/m3 and 4 g/m3
applied in two experimental settings to E. faecalis biofilms
and the effect of prolonged exposure times in setting 2
(1 min, 2.5 min, 5 min, 10 min).
Please note: Wiley-Blackwell are not responsible for the
content or functionality of any supporting information
supplied by the authors. Any queries (other thanmissing
material) should be directed to the corresponding author
for the article.
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Stress distribution of three NiTi rotary files underbending and torsional conditions using amathematic analysis
T. O. Kim1, G. S. P. Cheung2, J. M. Lee3, B. M. Kim3, B. Hur1 & H. C. Kim1
1Department of Conservative Dentistry, School of Dentistry, Pusan National University, Busan, Korea; 2Area of Endodontics,
Faculty of Dentistry, The University of Hong Kong, Hong Kong; and 3Division of Precision Manufacturing Systems, Pusan National
University, Busan, Korea
Abstract
Kim TO, Cheung GSP, Lee JM, Kim BM, Hur B, Kim HC.
Stress distribution of three NiTi rotary files under bending and
torsional conditions using a mathematic analysis. International
Endodontic Journal, 42, 14–21, 2009.
Aim To compare and evaluate the stress distribution
of three NiTi instruments of various cross-sectional
configurations under bending or torsional condition
using a finite-element analysis model.
Methodology Three NiTi files (ProFile, ProTaper
and ProTaper Universal) were scanned using Micro-CT
to produce a three-dimensional digital model. The
behaviour of the instrument under bending or torsional
loads was analysed mathematically in software (ABA-
QUS V6.5-1), taking into consideration the nonlinear
mechanical characteristic of NiTi material.
Results ProFile showed the greatest flexibility, fol-
lowed by ProTaper Universal and ProTaper. The
highest stress was observed at the surface near the
cutting edge and the base of (opposing) flutes during
cantilever bending. Concentration of stresses was
observed at the bottom of the flutes in ProFile and
ProTaper Universal instruments in torsion. The stress
was more evenly distributed over the surface of
ProTaper initially, which then concentrated at the
middle of the convex sides when the amount of angular
deflection was increased.
Conclusion Incorporating a U-shaped groove in the
middle of each side of the convex-triangular design
lowers the flexural rigidity of the origin ProTaper
design. Bending leads to the highest surface stress at or
near the cutting edge of the instrument. Stress
concentration occurs at the bottom of the flute when
the instrument is subjected to torsion.
Keywords: bending, cross-sectional geometry, finite-
element analysis, NiTi rotary file, stress distribution,
torsion.
Received 19 March 2008; accepted 16 August 2008
Introduction
Root canal instruments manufactured with nickel–
titanium (NiTi) have been developed in an attempt to
overcome the rigidity of instruments made from stain-
less steel alloys (Walia et al. 1988). NiTi instruments
possess a lower modulus of elasticity and a superior
resistance to torsional fracture, compared with stainless
steel instruments of similar size (Walia et al. 1988,
Schafer et al. 2003). The NiTi rotary instruments allow
root canal preparation to be accomplished more expe-
ditiously than hand instruments; a well-centred,
tapered root canal form with minimal risk of trans-
porting the original canal centre is often achieved
(Glosson et al. 1995, Garip & Gunday 2001, Schafer
2001, Chen & Messer 2002, Lee et al. 2003, Schafer
et al. 2004).
To date, many NiTi rotary systems have been
introduced to the market. Most brands, e.g. ProFile
(Dentsply Maillefer, Ballaigues, Switzerland), K3
(SybronEndo, Orange, CA, USA), Mtwo (VDW, Munich,
Germany) and Hero Shaper (Micro-Mega, Besancon,
Correspondence: Dr Hyeon-Cheol Kim, DDS, MS, PhD, Assis-
tant Professor, Department of Conservative Dentistry, Pusan
National University School of Dentistry, 1-10, Ami-dong,
Seo-gu, Busan 602-739, Korea (Tel.: +82 51 240 7978;
fax: +82 51 254 0575; e-mail: [email protected]).
doi:10.1111/j.1365-2591.2008.01481.x
International Endodontic Journal, 42, 14–21, 2009 ª 2009 International Endodontic Journal14
France) have a regularly tapered shaft, but with
different cross-sectional designs; some also possess
‘radial lands’ (Schafer 2001, Hata et al. 2002).
Amongst these systems, the ProFile system is best
known for its U-file design (i.e. with a concave, ‘U-
shaped’ flutes in cross-section; Fig. 1a), and for its
flexibility and better centering ratio than some other
systems (Park et al. 2003, Walsch 2004, Kim et al.
2005). In contrast, the ProTaper system (Dentsply
Maillefer) has a unique design for its shaft with a
‘progressively changing’ taper (Bergmans et al. 2003,
Clauder & Baumann 2004). The original cross-sec-
tional configuration of the ProTaper system was
triangular with convex sides (Fig. 1b). The sharp
cutting edge (instead of a radial land) is claimed to
reduce the contact area between the file and dentine,
thus enhancing the cutting efficiency of the instrument
(Clauder & Baumann 2004). However, it has been
reported that the ProTaper system tends to produce
more aberrations, transportation or straightening of
the canal (Yun & Kim 2003, Calberson et al. 2004,
Schafer et al. 2004). To overcome the problem, which
Figure 1 Schematic drawings of the cross-sectional and longitudinal geometry of three NiTi files after the real-size, three-
dimensional image from micro-CT: (a) ProFile size 30, 0.06 taper; (b) ProTaper F3 and (c) ProTaper Universal F3.
Kim et al. Stress distribution of NiTi rotary files
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 14–21, 2009 15
may be related to a slightly greater rigidity (partly
because of the cross-sectional area; another factor
being the taper of the instrument), compared with
ProFile instruments of similar cross-sectional dimen-
sion, a new version with a modified cross-sectional
design for the larger instruments of the original system
has been marketed as ProTaper Universal. The F2 and
F3 instruments of the ProTaper Universal system have
incorporated an additional groove in the middle of each
side of the ‘convex-triangular’ cross-section in an
attempt to increase its flexibility (Fig. 1c).
Clinically, there is a potential risk of rotary NiTi
instruments fracturing in the canal – even new
instrument may demonstrate unexpected failure in
use (Arens et al. 2003). On the other hand, little is
known about the distribution of stresses, an important
factor related to instrument fracture, when the instru-
ment is subjected to bending or torsional load. It has
been reported that fracture of an engine-file may occur
in either one or a combination of two ways: torsional
and flexural (i.e. fatigue) (Sattapan et al. 2000, Cheung
et al. 2005, Wei et al. 2007); the geometrical design is
an important determinant because of the effect on the
torsional and bending properties of the instrument
(Camps et al. 1995). Several studies of the stresses
generated in NiTi instrument have been completed
using finite-element (FE) analysis (Turpin et al. 2000,
2001, Berutti et al. 2003); however, they evaluated a
simulated, cylindrical shape and ignored the taper of
the root canal instrument when constructing the
models. Recently, Xu et al. (2006) have reported on
the effect of cross-section configuration on the mechan-
ical behaviour of root canal files by examining an
idealized cross-sectional configuration with FE analysis,
but they did not seem to have verified the actual
geometry of the real product. Indeed, there could be
discrepancies between the idealized design and the
actual product (Low et al. 2006). Thus, the purpose of
this study was to compare the stress distribution of the
two ProTaper designs under bending and torsional
stresses by inputting the actual shape of the instru-
ments for three-dimensional (3D) FE analysis. A U-file
design (ProFile) was also examined as a control.
Materials and methods
Modeling of NiTi rotary file
Real-size, digitized models of three brands of NiTi
instrument: ProFile size 30 (0.06 taper), ProTaper F3
and ProTaper Universal F3 (all from Dentsply Maillefer)
were obtained by first scanning them at 2-lm intervals
in a micro-CT scanner (HMX; X-Tek Group, Santa
Clara, CA, USA). Then, the outline of the instrument
was extracted from the stacks of 3D data in software
(IDEAS11 NX; UGS, Plano, TX, USA). Finally, a mesh of
linear, eight-noded, hexahedral elements was overlaid
onto the rendered 3D image. Such a 3D model
consisted of 11880 elements with 16318 nodes for
ProFile, 7560 elements with 9017 nodes for ProTaper,
or 8964 elements with 10668 nodes for ProTaper
Universal (Fig. 1). This numerical model of each
instrument was entered into a 3D FE analysis package
(ABAQUS V6.5-1; SIMULIA, Providence, RI, USA) with
the z-axis running from the tip to the shaft of the
instrument.
A nonlinear, stress–strain behaviour of the NiTi
material (Wang 2007) was entered for the NiTi
material during the mathematical analysis (Fig. 2):
OA represents the elastic deformation of austenite,
AB the pseudoelastic range (plateau spanning over
about 4% strain) because of stress-induced martensitic
(SIM) transformation, BC the elastic deformation of
martensite, and CD the plastic deformation of the
transformed martensite. Plastic deformation (a result of
because of crystallographic slip) is unrecoverable,
whereas elastic and SIM transformation strains are
mostly recoverable (Duerig & Pelton 1994). The
Young’s modulus of the alloy was 36 GPa and the
Figure 2 Stress–strain relationship of the NiTi material (from
Wang 2007).
Stress distribution of NiTi rotary files Kim et al.
International Endodontic Journal, 42, 14–21, 2009 ª 2009 International Endodontic Journal16
Poisson’s ratio 0.3. The critical stress at the beginning
of the SIM phase transformation was chosen to be
504 MPa and that at the end was 755 MPa (Wang
2007).
Experimental conditions of simulation
The behaviours of the three instruments were analysed
numerically under the following simulated conditions
in the FE analysis (Fig. 3):
1. Cantilever bending with a constant load – deforma-
tion in the form of cantilever bending was simulated by
applying a concentrated load of 1 N at the tip of the file
with its shaft rigidly held in place (Fig. 3a). The vertical
displacement was measured and the von Mises stress
distribution was evaluated.
2. Stress distribution under cantilever bending at fixed
displacement – under a similar condition as (a) above,
the tip of the file was deflected for a distance of 2 mm
(Fig. 3b) and held there. The von Mises stress distribu-
tion was examined.
3. Application of a shear moment (torsion) – a
2.5 Nmm moment of force was applied to the shaft in
a clockwise direction normal to the long axis of the
instrument (Fig. 3c), whilst 4 mm of the tip was rigidly
constrained. The stress distribution was evaluated.
4. Stress distribution at a fixed angular deflection – the
von Mises stress distribution over the instrument was
examined after the instrument was rotated by 10�clockwise with its tip rigidly fixed at 4 mm (Fig. 3d).
Results
Cantilever bending
At a concentrated load of 1 N, the end deflection for
ProFile was 4.6 mm, ProTaper 2.5 mm and ProTaper
Universal 3.1 mm, indicating a greater flexibility for
ProFile instrument. A maximum von Mises stress of
577 MPa was found at 8.4 mm from the tip of the
ProFile instrument; the values were 349 MPa at
3.7 mm for ProTaper, and 547 MPa at 3.6 mm for
ProTaper Universal (Fig. 4). The bending force required
to deflect the instrument from its resting position was
greatest for ProTaper, followed by ProTaper Universal
and ProFile (Fig. 5a). For the same amount of end
deflection (2 mm), a maximum von Mises stress of
387 MPa was noted for ProTaper Universal, again, at
3.6 mm from the instrument tip. The values were
350 MPa at 3.7 mm for ProTaper, and 275 MPa at
8.4 mm for ProFile instrument respectively (Fig. 6a).
The highest stress was observed at the surface at the
cutting edge of ProTaper, but at a very short distance
from such edge for ProTaper Universal and ProFile, and
at the base of the opposing flute during cantilever
bending.
Figure 3 Simulated conditions applied in this study: (a)
cantilever bending with a concentrated load of 1 N applied
to the tip of the instrument; (b) cantilever bending until the tip
was displaced by 2 mm; (c) Shear moment of 2.5 Nmm
applied to the shaft, with the instrument rigidly fixed at 4 mm
from its tip and (d) Similar condition as (c) but with the torque
applied until the shaft was rotated by 10�.
(a)
(b)
(c)
Figure 4 Relative deflection (to scale) of the tip, and stress
distribution under cantilever loading (1 N applied to the tip)
for each instrument: (a) ProFile; (b) ProTaper and (c) ProTaper
Universal.
Kim et al. Stress distribution of NiTi rotary files
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 14–21, 2009 17
Shear moment (torsion)
When a torque of 2.5 Nmm was applied, the original
ProTaper design showed the lowest value (350 MPa)
for the maximum von Mises stress, followed by
384 MPa for ProTaper Universal (Fig. 6b). The ProFile
showed the highest stress of 455 MPa, running along
at the base (bottom) of the U-shaped flutes. The angular
deflection was 0.691, 0.826 and 0.995 degrees for
ProTaper, ProTaper Universal and ProFile respectively.
The resistance to torsion mirrored the flexural
rigidity of the instrument: a higher torque was required
to angularly deflect the ProTaper than the other two
instruments (Fig. 5b). The highest von Mises stress
(constrained region not compared) recorded for ProFile
was 333 MPa, ProTaper 359 MPa and ProTaper
Universal 388 MPa, all situated at the base of the
flutes in cross-section (Fig. 6c).
Discussion
In the last decade, the use of NiTi rotary instruments
has grown in popularity and there has been an
increasing number of proprietary systems introduced
commercially. NiTi engine-files operate by way of
continuous rotation in the root canal and, as such,
are subjected to unidirectional torque (assuming no
stalling). The value of the shear (torsional) stress varies
depending on the canal size (Hubscher et al. 2003,
Peters et al. 2003), hardness of the dentine to be cut
(Berutti et al. 2003) and the use of a lubricant (Boessler
Figure 5 (a) Bending moment needed to deflect the tip and (b)
the torque required to rotate each file under the restrained
condition.
(a)
(b)
(c)
Figure 6 Distribution of von Mises stresses
under various conditions for the three
instruments tested, the maximum stress
values (in MPa) for each case being: (a)
ProFile 275, ProTaper 350, ProTaper
Universal 387; (b). ProFile 455, ProTaper
350, ProTaper Universal 384 and (c) ProFile
333, ProTaper 359, ProTaper Universal 388.
Stress distribution of NiTi rotary files Kim et al.
International Endodontic Journal, 42, 14–21, 2009 ª 2009 International Endodontic Journal18
et al. 2007). The cross-sectional configuration is also
an important determinant of the distribution of stresses
on the instrument (Tripi et al. 2006). To avoid dimen-
sional discrepancy, the three brands of NiTi instrument
examined in this present study were first scanned to
obtain a real representation of the 3D shape prior to
entry into the mathematical simulation.
Studies of NiTi instrument breakage are usually
completed by means of post-mortem SEM examination
of the fracture mode after clinical or simulated use.
Such evaluation would not reveal the stresses on the
instrument during bending or rotation. Based on a
mathematical comparison of the behaviour of two
theoretical cross-sections of ProTaper and ProFile, it
has been reported that ProTaper might be more
suitable for enlarging the (coronal portion of) canals
during the initial phase of shaping, and that ProFile
might be more suitable for wider canals and in the final
phase of shaping (Berutti et al. 2003). Turpin et al.
(2000) have studied the influence of the idealized cross-
sectional profile (ProFile vs. Hero) on the torsional and
bending stresses using a boundary integral method,
and also suggested that instruments of different cross-
sectional design should be used for different procedures.
The amount of end deflection under cantilever
loading is a measure of the instrument’s flexural
rigidity, the product of the elastic modulus of the
material and second moment of inertia of the part
(Timoshenko & Goodier 1970). ProFile had a greater
deflection than other systems, indicating that ProFile
possesses a lower flexural rigidity, i.e. higher flexibility.
As the mechanical property of the raw material is the
same for the three designs (from the same manufac-
turer), the difference in flexural rigidity of the various
makes is a result of the different geometry. ProTaper
had the greatest flexural rigidity, lower end deflection,
and the least concentration of stress over the surface
when subjected to a load of 1 N. Berutti et al. (2003)
have also reported that ProTaper had lower and more
evenly distributed stresses, compared with the ProFile
model, under similar type of loading. However, in the
clinical situation, the stress generated in an instrument
arises from it having to conform to the root canal
curvature (i.e. fixed deflection) but not due to an
externally applied force. Thus, the situation where the
various brands were subjected to the same amount of
end deflection (i.e. Fig. 3b) would be more relevant
than application of an arbitrary load – both the
ProTaper and ProTaper Universal showed a greater
value of internal stresses than ProFile. The highest
stress concentration was found at the cutting edge of
ProTaper and ProTaper Universal, and near the cutting
edge of the ProFile, and at the bottom of the directly
opposite flute (see Fig. 6a). This is expected from the
mechanics of bending a beam of triangular cross-
section. Generally, flexural (bending) deflection is
proportional to the bending moment and inversely
proportional to sectional modulus (Timoshenko &
Goodier 1970). A correlation between stiffness of an
instrument and its cross-sectional area has been
suggested in many studies (Haıkel et al. 1999, Turpin
et al. 2000, Schafer et al. 2003). In view of the similar
longitudinal outline of the ProTaper and ProTaper
Universal instrument, the addition of a groove (flute) at
the centre of each side of the ‘convex-triangular’ cross-
section has effectively reduced the second moment of
inertia for the latter. On the other hand, this groove
seems to have served as a stress-raiser in torsion.
The torsional rigidity, which is proportional to the
applied torque and the polar moment of inertia of the
part, was evaluated in the present study by measuring
the angular deflection of the instrument. ProTaper was
the most rigid, whereas ProFile the least. However,
unlike bending of the instrument being governed by the
canal curvature, shear stresses are generated in an
engine-file because of friction and the (resistance of
dentine to) cutting action. Thus, it would be more
logical to examine the stress distribution under a similar
torsional moment (Fig. 6b) rather than at the same
twist-angle (Fig. 6c). It seems that ProFile is going to
experience a much greater stress than ProTaper
instrument in such a situation (see Fig. 6c), a finding
corrobating that of other studies using FE analysis
(Turpin et al. 2000, 2001, Berutti et al. 2003, Xu et al.
2006). Concentrations of (torsional) stress were ob-
served at the bottom of the U-shaped flutes for ProFile
and at the concave groove at each side of the triangular
cross-section for ProTaper Universal, the stress of
which was much higher than that for the original
ProTaper. Hence, there is a greater chance of SIM
transformation, and even plastic deformation of the
transformed martensite there. This may explain a
higher reported incidence of unwinding defects (with
or without breakage) for discarded, clinically used,
engine-driven ProFile than ProTaper (Shen et al. 2006)
or K3 instrument (Ankrum et al. 2004). Enlarging the
canal to a size of 15 or 20 before using the instrument
would help to reduce the torsional stress experienced by
the instrument (Hubscher et al. 2003) and lower the
risk of shear fracture. Incorporating a U-shaped groove
for the original ProTaper design, i.e. ProTaper Uni-
versal, would lead to some stress concentration at the
Kim et al. Stress distribution of NiTi rotary files
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 14–21, 2009 19
bottom of the groove, as expected. It would be a weaker
point than with the ProTaper, but still be better than
ProFile in strength in order to resist torsion.
The reaction stresses in an instrument (of the same
material and dimensions) are dependent on the
geometry of the working part relative to the operating
load. Factors affecting the stress distribution include
the cross-sectional configuration, the depth of the
flute, area of the inner core and (the bulk of)
peripheral mass in cross-section; all these influence
the magnitude of the second and polar moments of
inertia. Not one of the systems studied was both
highly flexible and yet able to withstand and distribute
the stress evenly in bending and torsion. Indeed, it is
obvious that different parameters are operating when
the fracture susceptibility of an instrument (because of
torsion vs. rotational bending) is concerned (Cheung
et al. 2005). Clinicians should understand not only
the general guidelines for NiTi rotary instrumentation,
but also the structural characteristics which might
influence the durability or the risk of an engine-file to
fracture. To increase safety, endodontic educators
must emphasize the need for mastering the skill for
rotary instruments through appropriate, supervised
training (Mandel et al. 1999, Yared et al. 2001).
Despite a truer representation of the actual geometry
of the instrument in this study, the actual stresses
may differ when the instrument is actively filing
against the dentine wall during clinical use. Further
studies through other methods to verify the relation-
ship between instrument design, stress distribution,
fatigue fracture and the influence of microscopic
notches, are required.
Conclusions
This study examined the stress distribution under
bending or torsional load using a 3D FE analysis for
three NiTi instruments of various cross-sectional con-
figurations. It is concluded that the U-file design had
the lowest flexural rigidity, compared with a ‘convex-
triangular’ cross-section with or without an additional
flute, but a higher magnitude of stress concentration at
the bottom of the flute in torsion. Bending led to the
highest surface stress at or near the cutting edge of all
three instruments. The convex-triangular cross-section
was able to distribute the shear stresses initially, but
had similar stress concentrations at the same degree of
angular deflection. Incorporating a U-shaped groove for
the ProTaper design results in an instrument with
intermediate properties between the two.
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Kim et al. Stress distribution of NiTi rotary files
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 14–21, 2009 21
Ex vivo study on root canal instrumentation of tworotary nickel–titanium systems in comparison tostainless steel hand instruments
J. Vaudt1, K. Bitter1, K. Neumann2 & A. M. Kielbassa1
1Department of Operative Dentistry and Periodontology, University School of Dental Medicine, ChariteCentrum 3; and 2Institute
for Biometry and Clinical Epidemiology, ChariteCentrum 4; Charite – Universitatsmedizin Berlin, Berlin, Germany
Abstract
Vaudt J, Bitter K, Neumann K, Kielbassa AM. Ex vivo
study on root canal instrumentation of two rotary nickel–
titanium systems in comparison to stainless steel hand instru-
ments. International Endodontic Journal, 42, 22–33, 2009.
Aim To investigate instrumentation time, working
safety and the shaping ability of two rotary nickel–
titanium (NiTi) systems (Alpha System and ProTaper
Universal) in comparison to stainless steel hand
instruments.
Methodology A total of 45 mesial root canals of
extracted human mandibular molars were selected. On
the basis of the degree of curvature the matched teeth
were allocated randomly into three groups of 15 teeth
each. In group 1 root canals were prepared to size 30
using a standardized manual preparation technique; in
group 2 and 3 rotary NiTi instruments were used
following the manufacturers’ instructions. Instrumen-
tation time and procedural errors were recorded. With
the aid of pre- and postoperative radiographs, apical
straightening of the canal curvature was determined.
Photographs of the coronal, middle and apical cross-
sections of the pre- and postoperative canals were
taken, and superimposed using a standard software.
Based on these composite images the portion of
uninstrumented canal walls was evaluated.
Results Active instrumentation time of the Alpha
System was significantly reduced compared with Pro-
Taper Universal and hand instrumentation (P < 0.05;
anova). No instrument fractures occurred in any of the
groups. The Alpha System revealed significantly less
apical straightening compared with the other instru-
ments (P < 0.05; Mann–Whitney U test). In the apical
cross-sections Alpha System resulted in significantly
less uninstrumented canal walls compared with stain-
less steel files (P < 0.05; chi-squared test).
Conclusion Despite the demonstrated differences
between the systems, an apical straightening effect
could not be prevented; areas of uninstrumented root
canal wall were left in all regions using the various
systems.
Keywords: automated root canal preparation, NiTi
instruments, root canal aberration, root canal shaping,
working safety, working time.
Received 11 April 2008; accepted 16 September 2008
Introduction
The shaping ability of root canal instruments is often
assessed in terms of the preservation of the original root
canal curvature, and without creating iatrogenic
events such as instrument fracture, external transpor-
tation, ledges, or perforations (Weine et al. 1975,
1976). Good canal shaping through mechanical
instrumentation is generally considered essential be-
cause root canal shape may have an effect on the
efficacy of chemical disinfection.
In the last decade, several rotary nickel–titanium
(NiTi) instruments with different configurations and
designs have been developed with the aim to reduce the
preparation time and to simplify the preparation
procedure. Many of these systems have been investi-
gated with regard to their shaping and cleaning ability,
Correspondence: Juliane Vaudt, Abteilung fur Zah-
nerhaltungskunde und Parodontologie, ChariteCentrum 3
fur Zahn-, Mund- und Kieferheilkunde, Charite – Universitats-
medizin Berlin, Aßmannshauser Straße 4-6, D-14197 Berlin,
Germany (Tel.: +49-30-450 562 335 (332); fax: +49-30-450
562 932; e-mail: [email protected]).
doi:10.1111/j.1365-2591.2008.01489.x
International Endodontic Journal, 42, 22–33, 2009 ª 2009 International Endodontic Journal22
handling safety, and working time (Guelzow et al.
2005, Schirrmeister et al. 2006, Sonntag et al. 2007).
These studies have shown that NiTi instruments can
effectively prepare continuously tapered and centred
root canal forms exhibiting only minor deviations from
the main axis of the root canal (Paque et al. 2005,
Schafer et al. 2006, Sonntag et al. 2007). Moreover,
investigations have demonstrated that the use of NiTi
instruments decreased the prevalence and degree of
root canal transportation compared with hand instru-
ments (Schafer & Lohmann 2002, Schafer et al. 2004).
Nevertheless, these effects could not be entirely elim-
inated, and statistically significant differences concern-
ing the straightening effect between rotary NiTi
instruments have been reported (Yun & Kim 2003,
Yoshimine et al. 2005, Schafer et al. 2006). In most
studies the straightening effect has been analyzed
radiographically in the bucco-lingual direction only
(Guelzow et al. 2005, Paque et al. 2005, Schafer et al.
2006). Limited data exist about three-dimensional
morphological changes during preparation.
Total postoperative cleanliness can only be evaluated
histological or by using SEM techniques on longitudinal
or horizontal sections of extracted teeth (Hulsmann
et al. 2005). In addition, the pre- and post-instrumen-
ted root canal cross sections can be analyzed with
respect to unprepared canal walls, thus allowing for
conclusions regarding the mechanical cleaning ability.
The available literature reveals that rotary NiTi instru-
ments shape the coronal and middle third of the root
canal effectively, and create a smooth surface profile
(Foschi et al. 2004, Prati et al. 2004). It has been
reported that the apical third is the critical area of the
root canal, and remaining pulpal and inorganic debris
have been detected (Foschi et al. 2004, Prati et al.
2004). Interestingly, stainless steel hand instruments
revealed equal or even better results concerning
cleaning effectiveness when compared with NiTi
instruments (Schafer & Lohmann 2002, Prati et al.
2004). Various studies reported untreated root canal
wall areas after preparation using rotary NiTi instru-
ments (Peters et al. 2001, 2003). Root canal cleanli-
ness is also dependent on the size of the root canal
instrument. The available literature has revealed that
the use of larger apical instruments led to an advan-
tageous cleaning effect compared with smaller apical
files (Wu &Wesselink 1995, Bartha et al. 2006, Weiger
et al. 2006). However, root canal preparation with
large size instruments can weaken the root, and does
increase the risk of apical transportation (Wu et al.
2003).
In 2005, a newly developed rotary NiTi system
(Alpha System; Brasseler, Lemgo, Germany), and in
2006, an advanced rotary NiTi system (ProTaper
Universal; Dentsply Maillefer, Ballaigues, Switzerland)
were introduced into the market; only limited data exist
on the performance of these systems.
The Alpha System consists of three different instru-
ment sequences according to root canal anatomy
(small, average and large canals). The basic set consists
of five instruments with descending tapers ranging
from 10% to 2%, and sizes from 20 to 35. The
instruments are provided with a titanium nitride
coating, have a five-edged (pentagon) cross-section as
well as a noncutting safety tip. For coronal flaring, an
instrument with an increased taper, a square cross-
section (kite-shaped) and large chip spaces is available
(AF10; access reamer).
ProTaper Universal represents an advancement of
ProTaper, which has been previously investigated in
several studies (Calberson et al. 2004, Guelzow et al.
2005, Paque et al. 2005, Sonntag et al. 2007). The
basic sequence of ProTaper Universal exhibits an
advanced flute design that combines multiple tapers
within the shaft, a convex triangular cross-sectional
design, blades close to the noncutting pilot tip as well as
an increasing chip space (space for the accumulation of
debris) from tip to shaft. A new design feature of
ProTaper Universal NiTi system comprises the more
rounded tips of the finishing files with the aim to
increase the working safety as well as to improve
shaping ability. Furthermore, the cross-section design
has been modified. The convex lateral surfaces of F3 to
F5 are machined to increase its inherent flexibility.
The aim of the present study was to investigate the
instrumentation time, the working safety and the
shaping ability in extracted mandibular molar teeth
with curved root canals using the rotary NiTi systems
Alpha System and ProTaper Universal in comparison to
stainless steel hand instruments. A modified muffle
system was used to enable evaluation both in the
bucco-lingual and in the mesio-distal direction. The
hypothesis was that the parameters instrumentation
time, working safety and shaping ability would be
influenced by the instrumentation technique.
Materials and methods
Selection of teeth and experimental set-up
A total of 45 human mandibular molars (extracted for
periodontal reasons) with intact crowns and curved
Vaudt et al. Efficacy of two rotary NiTi instruments
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 22–33, 2009 23
mesial roots were selected. The study protocol con-
formed to the principles outlined in the Central German
Ethics Committee’s statement (Zentrale Ethikkommis-
sion 2007) focusing on the use of human body material
in medical research. Only teeth with completed root
formation, intact root apices, and without visible apical
resorption were included. Coronal access was achieved
using diamond burs, and the mesial root canals were
controlled for apical patency with a size 10 reamer
(VDW, Munich, Germany).
For evaluation of the several parameters a modifica-
tion of the muffle-block, as previously described by
Bramante et al. (1987), Campos & del Rio (1990) and
Hulsmann et al. (1999) was used. A muffle-block was
constructed, which allows removal and exact reposi-
tioning of the complete specimen or sectioned parts of
the latter (Fig. 1). Using this modified muffle, the
exposure of radiographs under reproducible conditions
in two directions (bucco-lingual and mesio-distal) was
guaranteed to take radiographs before, during and after
root canal preparation.
The muffle consisted of a ground section, four lateral
walls and a cover with eight vertical screws. The holder
for the radiographic sensor (fabricated from clear epoxy
resin) could be adjusted at the ground section of the
muffle, and the positioner for the X-ray tube could be
fixed at the outside of the ground part of the muffle
(Fig. 1).
Specimen preparation
The teeth were embedded into the muffle-block with
acrylic resin (Technovit 4071; Heraeus Kulzer, Hanau,
Germany), and shortened coronally to a length of
19 mm. Subsequently, specimens were sectioned hor-
izontally at 3, 6, and 9 mm from the apex (Sagemi-
krotom Leitz 1600; Leica Microsystem, Wetzlar,
Germany). The horizontal segments were remounted
into the muffle, and loss of material (300 lm, because
of the thickness of the saw blade as well as the inter-
slice thickness) was compensated using metal disks of
the corresponding height (300 lm).
An initial size 10 root canal instrument was inserted
into the curved root canal. Standardized radiographs
were taken prior to the instrumentation in a bucco-
lingual as well as in a mesio-distal direction with a
digital radiographic system (Planmeca intra; Planmeca,
Hamburg, Germany), operating at 70 kV and 7 mA.
Thus, the straightening of the instrumented root canals
could be evaluated from two directions to describe the
three-dimensional morphological changes during
preparation.
Root canal curvatures were measured according to a
modified method (Hulsmann & Stryga 1993) using the
software AxioVision (Carl Zeiss MicroImaging; Jena,
Germany). The specimens were divided into three
groups according to the root canal curvature (<25�,25�–35�, and >35�). On the basis of the degree of the
bucco-lingual curvature the teeth were randomized
equally into three groups of 15 teeth each (stratified
random sampling); thus, groups that were equal on the
matching variable were created.
With the aim to analyze the shaping ability and to
draw conclusions regarding the mechanical cleaning
ability of the systems photographs of the preoperative
coronal, middle, and apical cross-sections of the root
canals were taken using a stereo microscope (Stemi
SV11; Carl Zeiss, Oberkochen, Germany) including a
video camera attachment (JVC TK 1070E; Carl Zeiss) at
70· magnification.
Instruments and preparation technique
According to the manufacturers’ instructions all root
canals were initially prepared using a size 10 reamer
followed by a size 15 reamer. Alpha System files were
set into permanent rotation with a 4-level torque limit
setting ENDOadvance handpiece (KaVo; Biberach,
Germany), powered by an electric motor (MF-Perfecta;
W&H, Buermoos, Austria), and using a working speed
Figure 1 Insight into the modified muffle system with fixed
positioner for the X-ray tube (p) and inserted sectioned parts of
specimen (t), mounted for radiographic evaluation in vestib-
ulo-oral direction. The holder (h) bearing the slot for the
radiographic sensor (s) is adjusted at the ground section of the
muffle. The inserted small photograph reveals the tooth spec-
imen rotated at an angle of 90� to enable radiographic
evaluation in mesio-distal direction (for presentation, front
and side sections of the muffle-block have been removed).
Efficacy of two rotary NiTi instruments Vaudt et al.
International Endodontic Journal, 42, 22–33, 2009 ª 2009 International Endodontic Journal24
of 250 rpm (500 rpm for AF10). ProTaper Universal
instruments were set into permanent rotation with
a 4 : 1 reduction handpiece (WD-66 EM; W&H,
Buermoos) powered by a low torque-limited electric
motor (Endo IT control motor; VDW), and a working
speed of 300 rpm was used. Instrumental sequences
followed the manufacturers’ instructions (see Table 1).
The instruments were kept rotating inside the root
canal until they reached the working length and the
instruments designed for crown down technique
(AF10.045, AF06.025, AF04.025) were left in
the root canal for a short period of time (5–8 s).
The manual preparation technique was performed
using stainless steel K-Reamers (VDW) as well as
Hedstrom files (VDW). All root canals were preflared in
the coronal section with number 1 through three
Gates Glidden burs. The K-Reamers were used in a
reaming motion and manipulated in a clockwise
rotation of about 90–120� with a very light inward
force until the file reached the full working distance,
followed by a straight outward pull (turn-and-pull
motion). Hedstrom files were used additionally with
a withdrawing filing motion only. All instruments
were pre-curved. No step-back method of instru-
ment manipulation was used with the hand
instruments.
The individual working length for all specimens was
obtained by measuring the length of the initial
instrument (size 10; VDW) at the apical foramen
subtracting 1 mm. All files were used to instrument
only one canal and coated with a lubricant containing
EDTA (FileCare; VDW) before use. The root canals of all
teeth were instrumented up to size 30. After each
instrument, the root canal was irrigated with 2 mL of
1% NaOCl solution using a syringe and a 28-gauge
needle. All canals were instrumented and analyzed by
the same experienced operator.
Assessment of root canal preparation
Instrumentation time
The active time for root canal instrumentation was
recorded using a digital stopwatch (http://www.jumk.
de/stoppuhr; Internetservice Kummer + Oster, Buchen-
berg, Germany). Time for instrument changes as well as
irrigation times were not considered.
Working safety
The number of fractured instruments during instru-
mentation was documented.
Shaping ability
The assessment of the apical straightening effect for
each system was carried out after preparation up to
sizes 25 and 30, respectively. Radiographs were taken
with a size 25 and 30 instrument from both directions
Table 1 Total number of instruments used, sequence of preparation and working length (WL)
System Sequence
Alpha System (Brasseler, Lemgo, Germany;
five instruments)
Average canals (as indicated by the manufacturer)
AF10.045 – 10% taper, size 45 (canal orifice)
AF06.025 – 6% taper, size 25 (crown down to the curvature)
AF04.025 – 4% taper, size 25 (crown down to the curvature)
AF02.025 – 2% taper, size 25 (WL)
AF02.030 – 2% taper, size 30 (WL)
ProTaper Universal (Dentsply Maillefer,
Ballaigues, Switzerland; seven instruments)
S1 file (shaping file 1) - 2–11% taper, size 17 (canal orifice)
SX (auxiliary shaper file) - 3–19% taper, size 19 (canal orifice)
S1 (shaping file 1) - 2–11% taper, size 17 (WL)
S2 (shaping file 2) - 4–11.5% taper, size 20 (WL)
F1 (finishing file 1) - 7–5.5% taper, size 20 (WL)
F2 (finishing file 2) - 8–5.5% taper, size 25 (WL)
F3 (finishing file 3) - 9–5.5% taper, size 30 (WL)
Stainless steel instruments (Vereinigte
Dentalwerke, Germany; eight instruments)
Reamer - 2% taper, size 15 (WL)
Hedstrom file - 2% taper, size 15 (WL)
Reamer - 2% taper, size 20 (WL)
Hedstrom file - 2% taper, size 20 (WL)
Reamer - 2% taper, size 25 (WL)
Hedstrom file - 2% taper, size 25 (WL)
Reamer - 2% taper, size 30 (WL)
Hedstrom file - 2% taper, size 30 (WL)
Vaudt et al. Efficacy of two rotary NiTi instruments
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 22–33, 2009 25
(bucco-lingual and mesio-distal) (Fig. 2). Based on
the canal curvatures assessed pre- and postoperatively,
the apical root canal straightening was determined as
the difference between apical root canal curvatures
before and after instrumentation using instruments of
size 25 and 30, respectively.
In the coronal, middle and apical cross-sections of
the root canal the portion of uninstrumented canal
walls was evaluated. After root canal preparation
postoperative photographs of the cross sections were
taken. Pre- and postoperative photographs were super-
imposed using reference marks (Fig. 3) (Corel Draw;
Corel Corporation, Unterschleißheim, Germany).
On the basis of these images the distance of contact
between the pre- and postoperative root canal walls
was measured, and the portion of uninstrumented root
canal walls was determined (Fig. 3). According to the
results, specimens were divided into four groups:
Group 1: 0–25% contact between pre- and
postoperative cross-section/root canal wall.
Group 2: >25% contact between pre- and
postoperative cross-section/root canal wall.
Group 3: >50% contact between pre- and
postoperative cross-section/root canal wall.
Group 4: >75% contact between pre- and
postoperative cross-section/root canal wall.
Statistical analyses
The statistical analysis was conducted using one-way
anova with post hoc Tukey B tests for the active
(a) (b)
(c) (d)
Figure 2 Representative example of a series of radiographs
taken in vestibulo-oral (a) and mesio-distal direction before (c)
and after preparation up to ISO size 30 (b, d). The root canal
curvature was measured prior to instrumentation with the
initial instrument inserted (reamer ISO size 10) (a, c). Based on
the radiographs taken after preparation up to ISO size 30 (b,
d), canal curvature could be measured and apical straighten-
ing could be determined.
Figure 3 Representative superimposi-
tion of the pre- and postoperative
photographs of the root canal cross-
sections using reference marks (apical
area). The bolts demonstrate the edge of
the half-transparent superimposed
photograph of the instrumented canal.
The coloured lines show the traced root
canal outlines (red = initial outline;
black = outline after root canal prepa-
ration). Note that all root canal walls
were instrumented in this specimen.
Efficacy of two rotary NiTi instruments Vaudt et al.
International Endodontic Journal, 42, 22–33, 2009 ª 2009 International Endodontic Journal26
instrumentation time, and Kruskall–Wallis test fol-
lowed by pairwise comparisons using Mann–Whitney
U tests for the straightening effect. The Wilcoxon test
for paired samples was used for comparisons of both
directions (bucco-lingual and mesio-distal) regarding
the degree of straightening. The percentages of unin-
strumented root canal walls were compared using chi-
squared test (exact test was used). The level of
significance was set at a = 0.05 (without adjusting
for the respective comparisons, as the described pro-
ceeding is equivalent to the closed test procedure for the
particular case of three study groups). All statistical
analyses were performed using spss version 15.0
software (SPSS; Chicago, IL, USA).
Results
Working time
The active time for root canal instrumentation
(Table 2) was affected significantly by the systems used
(P < 0.0005; anova). The Alpha System required
significantly less time compared with the other systems
(P < 0.05; Tukey B), whereas ProTaper Universal
revealed a significantly reduced instrumentation time
compared with the manual technique (P < 0.05;
Tukey B).
Working safety
During the preparation of the curved root canals, no
fractures of any of the used instruments (stainless steel
files as well as the NiTi instruments) could be observed.
Shaping ability
The apical straightening of the curved root canals was
significantly affected by the instrumentation system
(Kruskall–Wallis). Results and P-values (for compari-
sons of all techniques, and with regard to the respective
preparations sizes) are summarized in Table 3. In
general, straightening was more pronounced with size
30 instruments compared with size 25; differences
amongst the groups were increased (as indicated by the
P-values) after use of size 30 instruments. In both
directions (bucco-lingual and mesio-distal), the use of
stainless steel instruments resulted in significantly
increased (P < 0.05; Wilcoxon) straightening if com-
pared with Alpha files; differences between ProTaper
Universal and the manual technique were not signif-
icant. No statistically significant differences between
the two directions regarding the degree of straightening
could be observed.
The analysis of the pre- and postoperative cross-
sections revealed that all systems used left uninstru-
mented root canal walls in all regions. For the coronal
and middle cross-sections no differences between the
systems were found with respect to uninstrumented
root canal walls (P > 0.05; Kruskal–Wallis). The
portion of uninstrumented root canal walls in the
apical cross-sections was significantly affected by the
instrumentation system (P = 0.004; chi-squared test);
the results are summarized in Table 4. Instrumentation
using the Alpha System resulted in significantly less
unprepared root canal walls compared with the man-
ual technique (P = 0.001; chi-squared test). Compar-
ison between ProTaper Universal and stainless steel
files did not reveal any significant differences
(P = 0.153; chi-squared test). ProTaper Universal left
more unprepared root canal walls compared with
Alpha System; however, this statistical difference was
only weakly significant (P = 0.043; chi-squared test).
Discussion
The aim of the present investigation was to compare
the shaping ability of two recently introduced rotary
NiTi instruments in contrast to a manual technique
using stainless steel instruments. The results revealed
significant differences between the used systems with
respect to their shaping ability as well as regarding the
working time. Thus, the hypothesis of the present study
concerning the differences between the systems regard-
ing the evaluated parameters could not be rejected.
Study design
Previous investigations that focused on the shaping
ability of NiTi instruments used either simulated root
canals (Yun & Kim 2003, Yoshimine et al. 2005,
Schirrmeister et al. 2006) or extracted human teeth
(Paque et al. 2005, Schafer et al. 2006). Simulated root
Table 2 Mean active preparation time (in s) and standard
deviation (SD)
System Mean SD
Alpha Systema 103.2 13.5
ProTaper Universalb 150.7 18.9
Manual techniquec 238.3 35.1
a,b,cMeans with differing superscript letters indicate significant
differences at a = 0.05.
Vaudt et al. Efficacy of two rotary NiTi instruments
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 22–33, 2009 27
canals using pre-fabricated resin blocks allow for
standardization of degree, location and radius of root
canal curvature in three dimensions as well as the root
canal length (Peters 2004, Hulsmann et al. 2005).
However, the hardness and abrasion behaviour of
acrylic resin and root dentine is not identical, and
consequently does not reflect the action of the instru-
ments in root canals of real teeth (Peters 2004,
Hulsmann et al. 2005). Therefore, using extracted
human teeth reflects the clinical situation more
adequately. Nevertheless, large variations concerning
root canal morphology and dentine hardness compli-
cate standardization of groups (Hulsmann et al. 1999).
Similar apical preparation diameters are required for
the comparison of the shaping and cleaning ability of
different root canal instruments. Thus, in all investi-
gated groups of the present investigation, the final
apical preparation diameter was size 30. Moreover, to
reduce the wide range of variations in three-dimen-
sional root canal configuration the present study used
mesial root canals of first and second mandibular
molars. These teeth reveal root canal curvatures in
most cases. Consequently, the measured degrees of the
root canal curvature were categorized into three groups
according to a modified method described by Schneider
(Schneider 1971); this matched-group design allowed
for minimization of high variations in the degree of
curvature between the groups.
To evaluate the quality of root canal preparation a
study design is desirable that allows for standardization
and facilitates simulation of the clinical situation.
Additionally, all relevant parameters should be
recorded. Root canal morphology and the effect of
instrumentation have been studied via numerous
techniques (Campos & del Rio 1990, Hulsmann et al.
1999).
A method has been introduced (Bramante et al.
1987) and modified (Campos & del Rio 1990, Huls-
mann et al. 1999) in which root canals can be
analyzed before and after instrumentation using
extracted teeth. Previously published literature has
described the varying configurations of the used muffle-
blocks (Campos & del Rio 1990, Hulsmann et al. 1999).
Various elements, horizontal and vertical grooves in
the walls of the muffle-blocks have been designed and
integrated to guarantee the exact reposition of the
specimen. In the present investigation a muffle-block
was constructed to evaluate simultaneously both
mechanical cleaning and shaping ability under
Table 3 Mean values (including standard deviations as well as minimum and maximum values) of apical straightening in
both directions (in degrees)
System
Straightening of vestibulo-oral direction (in degrees)
ISO size 25 ISO size 30
Mean SD Min Max Mean SD Min Max
Alpha System 0.6a 0.5 0.0 1.4 1.4a 1.0 0.2 3.8
ProTaper Universal 2.7a,b 2.8 0.0 9.2 4.3b 3.4 0.1 12.5
Manual technique 2.9b 3.0 0.1 9.4 4.4b 3.7 0.5 13.2
P-value (Kruskal-Wallis) 0.043 0.012
System
Straightening of mesio-distal direction (in degrees)
ISO size 25 ISO size 30
Mean SD Min Max Mean SD Min Max
Alpha System 1.7a 1.6 0.0 6.4 2.4a 1.9 0.1 7.0
ProTaper Universal 3.4b 2.2 0.0 7.7 4.4b 2.1 0.2 7.8
Manual technique 3.5b 2.9 0.1 11.7 4.7b 3.8 0.8 16.4
P-value (Kruskal-Wallis) 0.028 0.019
a,b,cSignificant differences (P < 0.05) according to comparisons using Mann–Whitney U test are indicated by different superscript
letters.
Table 4 Portion of uninstrumented area between superim-
posed pre- and postoperative root canal walls in the apical
region when viewed in cross-sections
System
Contact between pre- and
postoperative cross-section (%)
0–25% >25% >50% >75%
Alpha System Number 14 1 0 0
percentage 93.3% 6.7% 0.0% 0.0%
ProTaper
Universal
Number 8 5 2 0
percentage 53.3% 33.3% 13.3% 0.0%
Manual
technique
Number 3 10 1 1
percentage 20.0% 66.6% 6.7% 6.7%
Efficacy of two rotary NiTi instruments Vaudt et al.
International Endodontic Journal, 42, 22–33, 2009 ª 2009 International Endodontic Journal28
reproducible conditions. The elements were designed to
facilitate removal and exact repositioning of the com-
plete specimen or sectioned parts of the latter. On the
basis of the tapered internal space, integrated position-
ing devices as well as a cover, the exact and nonrelo-
catable vertical and horizontal position of the specimen
was guaranteed.
After sectioning of the embedded teeth horizontally,
the specimens were remounted into the muffle for
instrumentation. The loss of material was predictable
because of the use of the saw microtome, and could be
compensated using spacers (metal disks) of the same
height. The configuration of the used muffle system
allowed for evaluation of the root canal cross-section
prior, during and after instrumentation without chang-
ing the three-dimensional morphology of root canal.
A further important improvement was the ability to
evaluate the parameter ‘straightening of curved root
canals’ in two directions (bucco-lingual and mesio-
distal) with the aim to describe the three-dimensional
morphological changes during preparation. This
parameter refers to the maintenance of the original
shape of curved root canals, and provides information
about the direction of removed material.
Shaping ability
This study showed that root canal preparation using
stainless steel instruments as well as NiTi systems
results in a pronounced apical straightening effect in
the bucco-lingual as well as in the mesio-distal plane.
No differences were found between the two directions
regarding the degree of root canal transportation.
Various investigations demonstrated that the use of
NiTi instruments decreased the prevalence and degree
of root canal transportation compared with stainless
steel hand instruments (Schafer & Lohmann 2002,
Schafer et al. 2004). However, other studies reported
no differences between rotary NiTi systems and stain-
less steel hand instruments regarding root canal
transportation (Guelzow et al. 2005, Hartmann et al.
2007). These divergent outcomes might be explained
by differences in methodologies, methods of assessment,
instruments and preparation techniques.
A further aspect is the design of an instrument that
might influence the shaping ability. Stainless steel files
are relatively stiff that will increase with larger instru-
ment size and causes high lateral forces in curved root
canals (Bergmans et al. 2001, Schafer & Tepel 2001).
The rigidity of an instrument could be responsible for
straightening of and aberration from the root canal
(including ledges, zipping and perforations), along with
leaving significant portions of the root canal wall
uninstrumented (Peters et al. 2003, Calberson et al.
2004). It has been assumed that NiTi instruments
could improve shaping ability and minimize any
aberrations during root canal preparation (Paque et al.
2005, Yoshimine et al. 2005, Schirrmeister et al. 2006,
Sonntag et al. 2007). However, these effects could not
be entirely eliminated, and differences amongst rotary
NiTi instruments have been demonstrated (Yun & Kim
2003, Yoshimine et al. 2005, Schafer et al. 2006).
With regard to the reported outcomes, it has to be
stressed that different rake angles of instruments should
reveal varying cutting efficacies; indeed, most rotary
files have negative rake angles with a predominantly
scraping motion. In general, the shaping ability of root
canal instruments is a complex interrelationship of
various parameters such as cross-sectional design, chip
removal capacity, helical and rake angle, metallurgical
properties and surface treatment of the instrument
(Schafer 1999, Schafer & Oitzinger 2008).
The more rounded tip of the finishing files in the
ProTaper Universal sequence has been developed to
increase the working safety as well as to improve the
shaping ability. Furthermore, the cross-section design
has been modified to increase its inherent flexibility.
Obviously, the advanced design features of the ProTa-
per Universal system revealed similar results compared
with previous studies evaluating the classic ProTaper
files (Peters et al. 2003, Calberson et al. 2004, Sonntag
et al. 2007).
This study found a significantly pronounced apical
straightening effect in both directions using ProTaper
Universal compared to Alpha System. The different
instrument designs of these NiTi systems (i.e. progres-
sive versus constant taper) could have influenced the
observed outcomes. Previously published studies dem-
onstrated relationships between bending moment and
cross-section, file size as well as taper of an instrument
(Schafer & Tepel 2001, Schafer et al. 2003). The
ProTaper Universal files have multiple and increased
tapers within the shaft compared with the Alpha files
presenting a less and constant taper. The apical
transportation towards the outer aspects of the root
canal could have been affected by the variable tapers
along the cutting surface of the ProTaper Universal
files (up to 11% at the tip) compared with the
moderately tapered (2%) Alpha System instruments.
An increasing taper is associated with increased cross-
section areas and, accordingly, with decreased flexi-
bility of the files that could cause straightening and
Vaudt et al. Efficacy of two rotary NiTi instruments
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 22–33, 2009 29
root canal aberration during preparation (Bergmans
et al. 2001). The decreasing taper sequence of the
finishing files enhance the strength of the instruments,
but increase the stiffness of their tips (i.e. ProTaper
Universal size 30 is 9%, size 20 is 7%), thus resulting
in high lateral forces.
Previously published data about classic ProTaper
files showed similar results compared with the present
investigation and demonstrated varying degrees of root
canal straightening and transportation (Peters et al.
2003, Yoshimine et al. 2005). These tended at the mid-
point of the curvature towards the inner aspects and
apically towards the outer aspects of the root canal
(Calberson et al. 2004, Sonntag et al. 2007). An
investigation comparing three rotary NiTi instruments
has demonstrated a tendency to ledge or zip formation
at the end-point of preparation using ProTaper com-
pared with RaCe and K3 (Yoshimine et al. 2005). The
RaCe and K3 groups showed favourable results, and
the prepared root canals displayed a smooth shift to the
original root canals at the end point. The authors
recommended that more flexible instruments, like K3
and RaCe, should be used in the apical preparation of
curved root canals (Yoshimine et al. 2005). Compari-
sons amongst different rotary NiTi systems instruments
revealed more root canal straightening after use of
ProTaper compared to Mtwo, K3, ProFile, GT Rotary,
and Quantec (Yun & Kim 2003, Sonntag et al. 2007).
In contrast to these observations, other investigations
found no statistical differences in root canal transpor-
tation using ProTaper compared with other rotary NiTi
instruments after preparation of up to size 30 (Guelzow
et al. 2005, Paque et al. 2005).
The rotary NiTi Alpha System files provided a
centred apical preparation and maintained the original
shape of the curved root canals with only minor
deviation from the main axis. The files are character-
ized by a pentagon-type cross-sectional design resulting
in only slightly positive cutting angles and a compa-
rable low chip space (Schafer & Oitzinger 2008). The
reduced root canal transportation could be explained
by the high flexibility of these instruments because of
their minor and constant taper along the cutting
surface. This superior flexibility reduces the risk of root
canal transportation during the enlargement of curved
root canals (Schafer et al. 2003).
Furthermore, it has been shown that the cross-
sectional design as well as cross-sectional areas
mainly influenced bending properties of instruments
(Schafer & Tepel 2001, Schafer et al. 2003). It has
been reported that for identical working diameters, the
area of a triple-helix cross-section was found to be
approximately 30% greater than that of triple-U file
(Turpin et al. 2000). Because of the more massive
structure of a triple helix file, this instrument was
found to be less flexible than the triple-U instrument
(Turpin et al. 2000). The Alpha files used in the
present study had a pentagon-type cross-section. It
might be speculated that this form of cross-section
results in a high core diameter and a high cross-
sectional area compared with other forms (i.e. trian-
gular, square cross-section), and, consequently, in
reduced flexibility. Furthermore, the small chip space
could lead to apical blockage caused by insufficient
transportation of debris towards the orifice (Bergmans
et al. 2001). Alpha system files are the only known
rotary NiTi systems with a pentagon cross-sectional
design, and no published literature exists about this
design feature up to now.
Obviously, in the case of comparison between Alpha
System and ProTaper Universal the taper had a greater
influence on the flexibility than the cross sectional
design. Under the conditions of the present study the
use of the rotary NiTi Alpha System files resulted in
minimal apical root canal transportation. However, the
influence of the individual geometric characteristics of
the instruments on the cleaning and shaping ability
remains speculative.
It is well known that the surface hardness of NiTi
instruments is lower than that of stainless steel
instruments (Brockhurst & Hsu 1998, Schafer &
Oitzinger 2008). Consequently, the cutting efficiency
should be less compared with most stainless steel
instruments (Brockhurst & Hsu 1998). With the aim
to improve the surface hardness (and thereby increas-
ing the shaping efficiency of NiTi instruments) several
surface engineering techniques have been used, i.e.
physical vapour deposition (PVD) techniques. Recent
studies have shown that the PVD technique is suitable
to significantly increase the cutting efficiency of NiTi
instruments (Schafer 2002). However, those findings
did not corroborate the observation of a previously
published study comparing the cutting efficiency of
different NiTi systems (Schafer & Oitzinger 2008);
here, the results revealed no significant influence of
the PVD coating surface on the cutting efficiency, and
the Alpha System files showed a significantly lower
cutting efficiency compared with Mtwo, RaCe, and
Flexmaster (Schafer & Oitzinger 2008). Thus, the
influence of the PVD coating on the cutting efficacy of
NiTi instruments with different cross-sectional design
remains unclear.
Efficacy of two rotary NiTi instruments Vaudt et al.
International Endodontic Journal, 42, 22–33, 2009 ª 2009 International Endodontic Journal30
Unprepared root canal wall areas
The comparison of the pre- and postoperative photo-
graphs of root canal cross-sections enables conclusions
on shaping ability as well as mechanical cleaning
ability. The prepared root canal should include the
original root canal dimensions, and no unprepared
areas should remain (compare Fig. 3). In the present
investigation analysis of the pre- and postoperative
cross-sections showed that the manual technique using
stainless steel instruments as well as the rotary NiTi
systems left uninstrumented root canal walls in all
regions. While the coronal and middle cross-sections
demonstrated sufficient shaping outcomes with only
minor untreated areas, the percentage of uninstru-
mented root canal walls in the apical cross-section was
significantly affected by the instrumentation system.
Following preparation using the Alpha System the
specimens showed the lowest percentage of unprepared
root canal outlines compared with the manual tech-
nique using stainless steel instruments and the ProTa-
per Universal that ranged between the two previous
groups.
These findings corroborate the results of previous
studies. It has been reported that in the apical part of
the root canal amounts of remaining pulpal and
inorganic debris could be detected after using rotary
NiTi instruments (Foschi et al. 2004, Prati et al. 2004).
Furthermore, results indicated large untreated areas of
the root canal walls (Peters et al. 2001, 2003). These
areas tended to be on the convex curvature at mid-root
and the concave side of the curvature more apically
(Peters et al. 2003). Evaluation of the original ProTaper
resulted in untouched areas ranging from 43% to 49%
(Peters et al. 2003).
The superior shaping efficiency of the Alpha System
could be attributed to the high elasticity characteristics
of the instruments that resulted in minor root canal
transportation during root canal preparation. Conse-
quently, the files remove dentine uniformly on the
outer and inner side of the root canal and only minor
areas remain untouched. However, further studies
should evaluate whether the preparation of wide root
canals using the less tapered Alpha files will result in
sufficient cleanliness.
Nevertheless, the clinical significance of the param-
eter ‘prepared surface’ is not yet clarified. However,
when considering the fact that viable microbes may
penetrate deep into the dentinal tubules and may
persist during root canal treatment (Chuste-Guillot
et al. 2006), the need of an efficient irrigation (in
addition to the shaping regime) to clean the root canals
effectively is clearly highlighted.
Instrumentation time
The evaluation of the parameter ‘working time’ should
demonstrate the efficacy of a system and its clinical
suitability. Studies that investigated the working time
of various NiTi systems used the latter in different
treatment sequences and changing number of files.
Notwithstanding, working time depends on preparation
technique and operator experience.
Some investigations evaluated working time as the
active instrumentation time (summation of time taken
for files to work inside the root canal) (Paque et al.
2005). Other studies measured the working time
including the active instrumentation time as well as
the time for changing instruments and irrigation, thus
resulting in considerably higher values (Schirrmeister
et al. 2006). Evaluations of manual techniques and
rotary NiTi instruments have demonstrated huge
variations of working time, and cannot provide recom-
mendations for one of the two techniques (Schafer et al.
2004, Guelzow et al. 2005, Schirrmeister et al. 2006).
The present investigation observed shorter working
times for NiTi preparation compared with the manual
instrumentation. The results indicate that the ProTaper
Universal system required more time to prepare a root
canal than the Alpha System.
These results may be explained by the varying
number of instruments. In the present investigation,
root canal preparation was performed using eight
stainless steel files for the manual technique, and seven
files for ProTaper Universal. The five Alpha System files
exhibited the lowest number of required instruments
for root canal enlargement.
Working safety
The reasons for fractures of rotary NiTi instruments are
multifactorial, and complications can be attributed to
instrument design, manufacturing process, canal con-
figuration, applied force during instrumentation, prep-
aration technique, operator’s skills and experience as
well as the number of application inside the root canal
(Parashos & Messer 2006). In the present investigation
no fractures of the stainless steel files as well as the NiTi
instruments could be observed. All instruments were
used to instrument only one single root canal. It should
be emphasized that the regimen used was owing to the
objectives (to compare the cleaning and shaping ability
Vaudt et al. Efficacy of two rotary NiTi instruments
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 22–33, 2009 31
of different systems). Thus, this procedure does not
adequately reflect the clinical situation, and the clinical
relevance concerning the working safety should be
interpreted with caution.
Conclusion
Within the limitations of the present ex vivo study, the
experimental results suggest that none of the rotary
NiTi systems used was able to impede an apical
straightening effect during root canal preparation;
uninstrumented root canal wall areas were left in all
regions with all systems.
Few statistically significant differences amongst the
three instrumentation techniques could be revealed.
Instrumentation of curved root canals to ISO size 30
using instruments with greater taper (Pro Taper
Universal F2, F3) and stiffer instruments (Pro Taper
Universal F3, stainless steel file of size 30) seemed to
result in increased root canal transportation and in a
higher portion of unprepared root canal walls com-
pared with flexible NiTi instruments (Alpha 02/30)
that maintained the curvature of the root canal.
Acknowledgements
The authors are indebted to Brasseler (Lemgo,
Germany), Dentsply Maillefer (Ballaigues, Switzerland)
and Vereinigte Dentalwerke (Munich, Germany) for
generously providing the instruments.
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Dislocation resistance of ProRoot Endo Sealer, acalcium silicate-based root canal sealer, fromradicular dentine
B. P. Huffman1, S. Mai2, L. Pinna3, R. N. Weller4, C. M. Primus5, J. L. Gutmann6, D. H. Pashley7
& F. R. Tay4,7
1School of Dentistry, Medical College of Georgia, Augusta, GA, USA; 2Guanghua School of Stomatology & Institute of
Stomatological Research, Sun Yat-sen University, Guangzhou, China; 3Universita degli Studi di Cagliari, Reparto di Odontoiatria
Conservatrice, Sardinia, Italy; 4Department of Endodontics, School of Dentistry, Medical College of Georgia, Augusta, GA, USA;5Primus Consulting, Bradenton, FL, USA; 6Department of Endodontics, Baylor College of Dentistry, Texas A&M University System
Health Science Center, Dallas, TX, USA; and 7Department of Oral Biology, School of Dentistry, Medical College of Georgia, Augusta,
GA, USA
Abstract
Huffman BP, Mai S, Pinna L, Weller RN, Primus CM,
Gutmann JL, Pashley DH, Tay FR. Dislocation resistance
of ProRoot Endo Sealer, a calcium silicate-based root
canal sealer, from radicular dentine. International Endodontic
Journal, 42, 34–46, 2009.
Aim To examine the dislocation resistance of three
root canal sealers from radicular dentine with and
without immersion in a simulated body fluid (SBF),
using a modified push-out test design that produced
simulated canal spaces of uniform dimensions under
identical cleaning and shaping conditions.
Methodology Sixty single-rooted caries-free human
canine teeth were used. Standardized simulated canal
spaces were created using 0.04 taper ProFile instru-
ments along the coronal, middle and apical thirds of
longitudinal tooth slabs. Following NaOCl/ethylenedi-
amine tetra-acetic acid cleaning, the cavities were filled
with ProRoot Endo Sealer, AH Plus Jet or Pulp Canal
Sealer. After setting, half of the cavities were tested
with a fibre-optic light-illuminated push-out testing
device. The rest were immersed in SBF for 4 weeks
before push-out evaluation. Failure modes were exam-
ined with stereomicroscopy and field emission (FE)-
scanning electron microscopy.
Results Location of the sealer-filled cavities did not
affect push-out strengths. ProRoot Endo Sealer exhibited
higher push-out strengths than the other two sealers
particularly after SBF storage (P < 0.001). Failure
modes were predominantly adhesive and mixed for Pulp
Canal Sealer and AH Plus Jet, and predominantly
cohesive for ProRoot Endo Sealer. Spherical amorphous
calciumphosphate-like phases that spontaneously trans-
formed into apatite-like phaseswere seen in the fractured
specimens of ProRoot Endo Sealer after SBF storage.
Conclusions When tested in bulk without a main
core, both ‘sealer type’ and ‘SBF storage’ were signif-
icant in affecting push-out results. The ProRoot Endo
Sealer demonstrated the presence of spherical amor-
phous calcium phosphate-like phases and apatite-like
phases (i.e. ex vivo bioactivity) after SBF storage.
Keywords: calcium silicate-based sealer, dislocation
resistance, in vitro bioactivity, thin-slice push-out test.
Received 1 June 2008; accepted 16 September 2008
Introduction
The use of a sealer and a thermoplastic core material
for filling root canals is the accepted norm in contem-
porary root canal procedures. As leakage from the
apical or coronal direction is a possible cause of root
treatment failure (Madison & Wilcox 1988, De Moor &
Hommez 2000), a root canal sealer should exhibit good
sealing (Laghios et al. 2000) and adhesive properties
(Wennberg & Ørstavik 1990, Gettleman et al. 1991,
Timpawat et al. 2001, Lee et al. 2002a,b, Saleh et al.
2003, Tagger et al. 2003). A sealer may be
Correspondence: Dr Franklin R. Tay, Department of Endodon-
tics, School of Dentistry, Medical College of Georgia, Augusta,
GA, 30912-1129, USA (Tel.: +1 706 7212033; fax:
+1 706 7216252; e-mail: [email protected]).
doi:10.1111/j.1365-2591.2008.01490.x
International Endodontic Journal, 42, 34–46, 2009 ª 2009 International Endodontic Journal34
conceptualized as a joint created between the radicular
dentine and the filling material. Similar to other
prosthetic joints in the body, the ability to resist
dislocation during function is crucial to their survival
(Scifert et al. 1999, Weale et al. 2002, He et al. 2007).
For a root canal sealer, the ability to resist disruption of
the established seal via micromechanical retention or
friction is highly desirable during intraoral tooth
flexure (Panitvisai & Messer 1995) or preparation of
cores or postspaces along the coronal- and middle-
thirds of canal walls (Munoz et al. 2007).
Predictable clinical results have been reported with
the use of gutta-percha in conjunction with zinc oxide
eugenol or epoxy resin-based root canal sealers (Saleh-
rabi & Rotstein 2004, Tilashalski et al. 2004). Never-
theless, there is a continuous quest for alternative
sealers or root filling materials with better seal and dis-
location resistance. Although the correlation between
the sealing property of a root canal sealer and its
adhesive characteristics has not been firmly esta-
blished, it is essential that the dislocation resistance of
a root canal sealer to dentine is not adversely affected
by the seepage of body fluids when there is a breach of
either the apical or coronal seal.
ProRoot Endo Sealer (Dentsply Tulsa Dental Special-
ties, Tulsa, OK, USA) is an experimental calcium
silicate-based root canal sealer that is designed to be
used in conjunction with a root filling material in either
the cold lateral, warm vertical or carrier-based filling
techniques. The major components of the powder
component are tricalcium silicate and dicalcium sili-
cate, with the inclusion of calcium sulphate as a setting
retardant, bismuth oxide as a radiopacifier and a small
amount of tricalcium aluminate. The liquid component
consists of a viscous aqueous solution of a water-
soluble polymer. Similar to other tricalcium silicate and
dicalcium silicate-containing biomaterials, the sealer
produces calcium hydroxide on reaction with water
(Gou et al. 2005, Camilleri & Pitt Ford 2006, Wang
et al. 2008). It is also anticipated that release of
calcium and hydroxyl ions from the set sealer will
result in the formation of apatites as the material comes
into contact with phosphate-containing fluids (Sarkar
et al. 2005), via spontaneous transformation from
initial amorphous calcium phosphate phases (Tay et al.
2007, Tay & Pashley 2008).
Whereas the retentive potential of geosynthetics
(Marques 2005), concrete reinforcements (Lee et al.
2002a,b) and rigid postsystems within canal spaces
(Mitchell et al. 1994, Teixeira et al. 2006) may be
evaluated en masse using conventional pull-out test
designs, thermoplastic root filling materials and sealers
are not amendable to gripping that is a prerequisite for
this type of mechanical testing (Goracci et al. 2007).
Thus, the thin-slice push-out test has been used quite
frequently for evaluating the dislocation resistance of
root filling materials (Gesi et al. 2005, Sousa-Neto et al.
2005, Gancedo-Caravia & Garcia-Barbero 2006, Skid-
more et al. 2006, Ungor et al. 2006, Bouillaguet et al.
2007, Fisher et al. 2007, Jainaen et al. 2007, Nagas
et al. 2007, Sly et al. 2007, Ureyen Kaya et al. 2008).
The strength of that experimental design is that each
horizontal root slab being tested is derived from a root
filled canal and contains a cross-section of the thermo-
plastic root filling material and sealer to be investigated.
In the present study, a modified thin-slice push-out test
was designed to evaluate the dislocation resistance of
root canal sealers that were applied in bulk to simu-
lated canal spaces without the use of thermoplastic
material cores. The null hypothesis tested was that
there are no differences in the dislocation resistance of
three root canal sealers from radicular dentine when
the set sealers are tested with and without immersion
in a simulated body fluid (SBF).
Materials and methods
Preparation of simulated canal spaces
Sixty intact, caries-free human canine teeth were
collected after the patients’ informed consents were
obtained under a protocol reviewed and approved by
the Human Assurance Committee of the Medical
College of Georgia, Georgia, USA. For each tooth, a
0.90 ± 0.05 mm thick longitudinal slab was prepared
by making buccolingual sections parallel to the longi-
tudinal axis of the tooth using a slow-speed diamond
saw (Isomet; Buehler Ltd, Lake Bluff, IL, USA) under
water-cooling. A Plexiglas platform containing a cylin-
drical well was affixed to the base of a mini drill press
to generate vertically oriented, truncated cavities of
uniform dimensions within the tooth slab (Fig. 1a).
A 0.6 mm drill bit was first used to prepare pilot holes
in the radicular dentine adjacent to the dental pulp.
Each pilot hole was carefully drilled so that it was
equidistant from the cementum and the canal wall.
Two pilot holes each were prepared in the coronal,
middle and apical thirds of the root.
Each hole was subsequently enlarged using a size 40,
25 mm long 0.04 taper ProFile nickel titanium rotary
instrument (Dentsply Tulsa Dental Specialties). To
ensure optimal cutting efficacy, a new instrument
Huffman et al. Dislocation resistance of ProRoot Endo Sealer
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 34–46, 2009 35
was used for each tooth slab. The drill press and the
thickness of the Plexiglas platform were configured so
that the rotary instrument penetrated the cylindrical
well to the same depth every time (Fig. 1b). This
permitted preparation of all truncated cavities to the
D16 diameter of the rotary instrument (i.e. 1.04 mm)
along the surface of the tooth slab. Inadvertent
preparation of cavities with nonvertical extrusion paths
was prevented by aligning the rotary instrument
perpendicular to the tooth slab (Fig. 1c). The experi-
mental design ensured that all cavities created in the
coronal, middle and apical thirds of the roots had
comparable dimensions. The artificial canal spaces
were also completely devoid of calcospherites that are
found along the mineralization front of the noninstr-
umented portions of natural root canal spaces. This
eliminated the issue of unpredictable augmentation in
sealer dislocation resistance that is caused by the
presence of undercuts and increased contact areas in
calcospherite-containing canal walls. The tooth slabs
were divided randomly into six groups of 10 slabs each
for evaluation of three endodontic sealers with or
without immersion in a SBF. Six cavities were created
in each tooth slab, with the two apical cavities residing
in transparent, sclerotic radicular dentine (Fig. 1d). For
each group, 20 simulated canal spaces were available
Figure 1 Experimental setup for the preparation of perpendicular truncated cavities of uniform dimensions in different locations
of a longitudinal tooth slab. (a) A mini drill press (D) with a 25 mm thick Plexiglas platform (B) affixed to its base (pointer).
(b) A tooth slab was placed over a supporting well in the Plexiglas platform. A 0.04 taper size 40 Profile nickel titanium rotary
instrument was inserted through a pre-drilled pilot hole in the tooth slab to create a truncated hole with the basal diameter
corresponding to the D16 diameter (i.e. 1.04 mm) of the rotary instrument. The drill press was set to drill exactly to the same depth
every time to ensure that each hole has the same circumference. (c) As slanted preparations are not amendable to push-out
testing, the current setup ensured that all cavities were created perpendicular to the tooth slab. (d) Two tapered cavities each were
prepared in the apical (Ap), middle (Mi) and coronal (Co) thirds of the root dentine. Pointer: cementoenamel junction; open
arrowhead: cementum.
Dislocation resistance of ProRoot Endo Sealer Huffman et al.
International Endodontic Journal, 42, 34–46, 2009 ª 2009 International Endodontic Journal36
from each of the three respective radicular dentine
locations (n = 20).
Filling of root canal sealers
The tooth slabs were immersed in 17% ethylenedia-
mine tetra-acetic acid (EDTA) and ultrasonicated for
5 min to dissolve the smear layer created during the
hole-shaping procedures. The slabs were further
immersed in 6.15% sodium hypochlorite and ultraso-
nicated for 5 min to remove organic debris and the
demineralized collagen matrix created during EDTA
application. The rationale for en masse cleaning was to
further ensure that differences in dislocation resistance
of the sealers from different dentine locations were not
caused by inadequate cleaning of the apical radicular
dentine.
The three sealers investigated in this study were Pulp
Canal Sealer (SybronEndo; Sybron Dental Specialties
Inc., Orange, CA, USA), AH Plus Jet (Dentsply Caulk,
Milford, DE, USA) and the experimental ProRoot Endo
Sealer. The former two sealers were mixed according to
the manufacturers’ instructions. The calcium silicate-
based sealer was mixed with a liquid-to-powder ratio of
1 : 2 and covered with moist gauze to avoid evapora-
tion of the water component. All cavities from one
tooth slab were filled with one type of sealer. Each tooth
slab was placed over a Mylar strip (Angst & Pfister,
Geneva, Switzerland), which in turn was placed over a
microscope glass slide. For Pulp Canal Sealer and
ProRoot Endo Sealer, the sealer was mixed and placed
inside a 19-gauge AccuDose Needle Tube (Centrix,
Shelton, CT, USA). The sealer was dispensed into the
cavities so that each hole was filled with excess sealer.
For AH Plus Jet, the sealer was dispensed directly from
the double-barrel mixing syringe via an intraoral tip
attached to an auto-mixing tip. The surface of the tooth
slab was then covered with another Mylar strip and a
glass slide. The assembly was secured with binder clips
so that excess sealer was expressed laterally from the
surface and bottom Mylar strips. The assemblies were
transferred to humidors and stored under 100%
relative humidity for 1 week until all the sealers had
completely set.
The binder clips were released and the Mylar strips
were removed from the tooth slab to expose the set
sealers. The top and bottom surfaces of each tooth slab
were polished with 800-grit silicon carbide papers
under running water to remove the excess sealer. For
each sealer, one subgroup of 10 tooth slabs was tested
immediately after polishing, whilst the other subgroup
of 10 tooth slabs was immersed for 4 weeks at 37 �C in
a phosphate-containing SBF prior to testing. The SBF
contained 136.8 mmol L)1 NaCl, 3.0 mmol L)1 KCl,
2.5 mmol L)1 CaCl2Æ6 H2O, 1.5 mmol L)1 MgCl2Æ6-H2O, 0.5 mmol L)1 Na2SO4Æ10 H2O, 4.2 mmol L)1
NaHCO3 and 1.0 mmol L)1 K2HPO4Æ3H2O in deionized
water (pH 7.4). To prevent bacterial growth, 0.02%
sodium azide was also included in the SBF.
Dislocation resistance evaluation
The dislocation resistance of the set root canal sealers
was evaluated using a thin-slice push-out test design
(Chandra & Ananth 1995, Chandra & Ghonem 2001).
Prior to testing, the thickness of each tooth slab was
measured to the nearest 0.01 mm using a pair of
digital calipers. A 0.7 mm diameter carbon steel
cylindrical plunger was used for the push-out test.
The plunger had a clearance of about 0.1 mm from
either side of the dentinal wall when it is perfectly
aligned with the apical part of the truncated hole. The
plunger was attached to a 10 kg load cell that was
connected to a universal testing machine (Vitrodyne
V1000 universal tester; Liveco Inc., Burlington, VT,
USA). The push-out device consisted of a clear
Plexiglas platform with a vertical cylindrical channel,
which served as the support for the tooth slab and
provided space for the vertical movement of the
plunger through the truncated hole (Fig. 2a). To
ensure optimal alignment of the plunger with the
sealer-filled hole, a horizontal channel was drilled
through the Plexiglas platform into the vertical chan-
nel (Fig. 2b). A fibre-optic light guide was inserted into
the horizontal channel to provide high intensity
illumination of the truncated hole during the align-
ment procedure. Each root slab was secured with
sticky wax in an apical-coronal direction to the
supporting Plexiglas platform, so that the smaller
diameter apical side of the sealer-filled hole was facing
the plunger. Each sealer-filled hole was subjected to
compressive loading at a cross-head speed of
10 lm s)1 in order to displace the set sealer toward
the coronal aspect of the hole. As the plunger contacts
the set sealer on loading, shear stresses were intro-
duced along the sealer-dentine interface, causing the
set sealer to be dislocated from the walls of the
radicular dentine. Failure was confirmed by the
appearance of a sharp drop along the load/displace-
ment curve recorded by the testing machine. After
performing push-out testing of the first hole, the tooth
slab was carefully removed and realigned with the
Huffman et al. Dislocation resistance of ProRoot Endo Sealer
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 34–46, 2009 37
second hole. The procedures were repeated until the
set sealers were dislodged from all the six cavities
within a tooth slab. After the push-out test, each root
slab was examined with a stereomicroscope at 30·magnification to determine the mode of failure. Failure
modes were classified as: adhesive failure along the
sealer-dentine interface; cohesive failure within the
sealer, and mixed failure that consisted of partial
adhesive failure along the dentinal walls and partial
cohesive failure within the sealer (Fig. 2c).
Digitized photographs of each tested hole were taken
from the coronal and apical aspects of the tooth slab
together with a millimetre scale for calibration purpose.
Such a procedure was performed after completion of
the push-out test as this permitted better contrast of the
circumference of the cavities. The circumferences of the
coronal (C) and apical aspects (A) of each cavity were
measured from the digitized images using image
analysis software (Image 4.01; Scion Corp., Frederick,
MA, USA). The area of the sealer-dentine interface was
approximated by 0.5 · (C + A) · h, where h represents
the thickness of the tooth slab. Dislocation resistance of
the sealer, as represented by the push-out strength, was
computed by dividing the maximum load (N) derived
from the load displacement curve with the sealer-
dentine interfacial area (mm2) and expressed in mega-
Pascals (MPa). The same procedures were applied to
those tooth slabs that had been immersed in SBF for
4 weeks.
Statistical analysis
Each sealer-filled hole was treated as a statistical unit.
For each of the six subgroups, data (n = 20) from the
three radicular dentine locations (i.e. coronal, middle
and apical thirds) were analysed using one-way anova
to determine if dislocation resistance of a particular
sealer was affected by the location of the sealer. As there
were no differences in the dislocation resistance amongst
dentine locations in all the six subgroups, data from the
coronal, middle and apical aspects of each subgroup
were pooled together for further analysis (n = 60). As
the pooled data were not normally distributed, log10-
transformation of the data was performed to normalize
the data before statistical evaluation. The transformed
pooled data were evaluated using a two-way anova
design, with sealer type and SBF storage as independent
variables. Post hoc pair-wise comparisons were per-
formed using Tukey multiple comparisons. The Student
paired t-test was conducted within the same sealer type
to examine if there was difference between the subgroup
that was tested without SBF immersion and the other
Figure 2 Experimental setup for the thin-slice push-out test. (a) The plunger (P) was connected to a 10 kg load cell (L). The
plunger was aligned with the cylindrical well (arrow) of a clear Plexiglas stage. The latter had a side channel (open arrowhead) for
the fitting of a fibre-optic light guide. (b) Each tooth slice was placed on top of the cylindrical well. The plunger had a diameter of
0.7 mm whilst the truncated hole had diameters of about 0.94 and 1.04 mm along its top and base. The use of light illumination
ensured that the plunger was aligned with the centre of the hole so that the sealer was pushed out without the plunger contacting
the wall of the hole. (c) Examples of adhesive failure, mixed failure and cohesive failure of the sealers, as observed through a
stereomicroscope after the push-out test.
Dislocation resistance of ProRoot Endo Sealer Huffman et al.
International Endodontic Journal, 42, 34–46, 2009 ª 2009 International Endodontic Journal38
that was tested after SBF immersion. Statistical signifi-
cance was set at a = 0.05.
Scanning electron microscopy
After push-out testing, two slabs from each of the six
subgroups were air-dried, sputter-coated with gold/
palladium, and examined using a field emission scan-
ning electron microscope (Model XL-30 FEG; Philips,
Eindhoven, The Netherlands) at 15 KeV. The objective
of the morphologic examination was not to reiterate
the assessment of failure modes that had been per-
formed using stereomicroscopy. Rather, the higher
resolution of a field emission microscope was utilized to
substantiate whether calcium phosphate-like phases
and their phase transformation could be identified after
the calcium silicate-based sealer was immersed in the
phosphate-containing SBF.
Results
Representative load–displacement curves of the three
root canal sealers are shown in Fig. 3a. Despite the
differences in the magnitude of the maximum load
achieved in the three sealers, their load–displacement
curves demonstrated were characterized by four
regions. There was an initial linear increase in load
(zone I) that corresponded with the increase in shear
stresses along the sealer-dentine interfaces as
the compressive load was applied from the base of the
inverted truncated sealer core. Prior to reaching the
maximum compressive load, the shear stresses reached
a critical value whereupon delamination was initiated
from the top of the inverted core. The increase in
Poisson’s ratio along the nondelaminated part of the
core (i.e. expansion) resulted in increased work to
continue the delamination and hence a change in the
slope of the load–displacement curve (zone II). Upon
reaching the maximum load, propagation of shear
stresses toward the bottom of the interface resulted in
complete interfacial delamination and a sudden sharp
drop in the recorded load (zone III). During the final
push-out phase (zone IV), resistance to displacement by
sliding friction and surface roughness of the delami-
nated sealer core resulted in a progressive, less abrupt
decline in the recorded load as the delaminated core
was displaced out of the truncated hole.
For each sealer with or without SBF immersion, no
significant differences were observed amongst the push-
out strengths obtained from different dentine locations
(Fig. 3b). Thus, data from the apical, middle and
coronal thirds of the roots were pooled to provide a
more robust analysis of the effects of sealer type and
SBF immersion on push-out strengths (Fig. 3c). When
the specimens were tested without SBF immersion,
significant differences (P < 0.001) were observed
amongst the three sealers, with the calcium silicate-
based sealer producing the highest push-out strength
(16.2 ± 6.5 MPa) followed by AH Plus Jet (3.5 ±
1.7 MPa) and Pulp Canal Sealer (0.7 ± 0.6 MPa) in
decreasing order. Significant differences in push-out
strength was also observed for specimens that were
tested after they were immersed in SBF for 4 weeks
(P < 0.001), following the same order as previously
described (calcium silicate-based sealer 22.4 ±5.0 MPa;
AH Plus Jet 6.6 ± 1.7 MPa; Pulp Canal Sealer
0.4 ± 0.3 MPa). Interaction of these two factors were
also significant (P < 0.001). For the AH Plus Jet and
the calcium silicate-base sealer, Student paired t-tests
revealed significant differences (P < 0.05) between the
push-out strengths generated from specimens that were
tested without SBF immersion and those that were
tested after immersion in SBF.
The per cent distribution of failure modes amongst
the six subgroups is presented in Fig. 4. No cohesive
failure was observed for Pulp Canal Sealer. This sealer
also exhibited an increase in the percentage of adhesive
failure after storage in SBF. A preponderance of mixed
failures was seen in AH Plus under the two storage
conditions, whilst cohesive failures within the sealer
were predominantly identified for the calcium silicate-
based sealer.
Under scanning electron microscopy, failures classi-
fied as adhesive failures in the Pulp Canal Sealer groups
invariably contained some sealer remnants along the
dentinal walls (not shown). However, the overall
impressions of those dentinal walls were still relatively
smooth when compared with the mixed failures
observed in the other sealer groups. A cohesive failure
in AH Plus Jet after SBF immersion is shown in Fig. 5a.
A high magnification view of the fractured sealer
surface revealed characteristic multi-faceted fillers that
were partially embedded, amongst other smaller fillers,
within a resinous matrix (Fig. 5b). A mixed failure
mode in the calcium silicate-based sealer after SBF
immersion is depicted in Fig. 6a. Spherical bodies were
identified along the sealer–dentin interface as well as
the surface of the fractured sealer (Fig. 6b). These
spherical phases were not observed from fractured
specimens of the same sealer that had not been
immersed in SBF (not shown). Very high magnification
views of the specimens that had been immersed in SBF
Huffman et al. Dislocation resistance of ProRoot Endo Sealer
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 34–46, 2009 39
before testing revealed phase transformation of the
spherical bodies to spherules with clustered polycrys-
talline surfaces (Fig. 6c). Individual crystallites that
protruded from the surface of these spherules were
about 40–70 nm in diameter (Fig. 6d).
Discussion
This study utilized a modified push-out protocol that
was designed specifically to examine the retentive
potential of sealers in radicular dentine. Although the
study design is far removed from clinical practice, the
results indicate that under identical cleaning and
shaping conditions that may not be easily achieved
under a clinical setting, the dislocation resistance of a
particular sealer is independent of the location of the
radicular dentine. Moreover, the dislocation resistance
of the three sealers were significantly different from
each other and that two of the three sealers exhibited
higher dislocation resistance after immersion in SBF.
Thus, the null hypothesis has to be rejected. Although
a modified push-out test design was used in this study,
it is interesting to note that the relatively low push-out
strengths for AH Plus and Pulp Canal Sealer were
similar to the range reported for similar sealers
(2.00 ± 0.65 MPa for AH Plus and 0.79 ± 0.52 MPa
for Kerr EWT sealer) in a previous study (Fisher et al.
2007).
Although testing designs that involve the use of
natural canal spaces have obvious pragmatic appeal to
clinicians, there are severe limitations from a materials
science perspective. First, the application of a compres-
sive load on top of a thermoplastic material, which has
Load-displacement curves of endodontic sealers(a)
(b)
(c)
Push out strength of endodontic sealers
Push out strength of endodontic sealers(pooled results; N = 60)
Displacement (μm)
Ap: Apical thirdMi: Middle thirdCo: Coronal third
Before immersion in SBFAfter immersion in SBF for4 weeks
Before immersion in SBFAfter immersion in SBF for4 weeks
70
60
50
40 I
II
III
IV30
20
10
00 200 400
ProRoot Endo SealerAH Plus Jet Pulp Canal Sealer
600 800 1000
30
25
20
15
10
5
0
Lo
ad (
N)
MP
a
25
20
15
10
5
0Pulp Cancal
SealerAH Plus Jet ProRoot Endo
Sealer
Pulp Cancal Sealer
Ap Mi Co Ap Mi Co Ap Mi CoAH Plus Jet ProRoot Endo
Sealer
3 C
2
B
1A
Dis
loca
tio
n r
esis
tan
ce (
MP
a)
Figure 3 Push-out strength results. (a) Representative load-
displacement curves of the three sealers that were tested in
bulk without an accompanying gutta-percha core. Load is
expressed as Newtons (N) and displacement is expressed as
microns (lm). Zone I: initial linear increase in load; zone II:
change in slope of the load–displacement curve before
reaching maximum load; zone III: initial sudden sharp drop
in recorded load upon interfacial delamination; zone IV: final
push-out phase. When magnified, the four regions described
for ProRoot Endo Sealer could also be seen in the load–
displacement curves of AH Plus Jet and Pulp Canal Sealer. (b)
dislocation resistance (expressed as MPa) of the three sealers in
the apical third (Ap), middle third (Mi) and coronal third (Co)
of the root dentine with and without storage in a simulated
body fluid (SBF) (n = 20/location/storage subgroup). As there
were no statistical differences in the push-out strengths of each
sealer amongst different locations at each time period, data
from the three locations were pooled (n = 60) for subsequent
statistical comparisons. (c) The pooled data was analysed
using a two-way anova design with sealer type and SBF
storage as independent variables. For specimens tested without
SBF immersion, sealers with different numerals above their
corresponding data columns represent significant differences
(P < 0.001). For specimens that were tested after they were
immersed in SBF, sealers with different upper case letters
above their corresponding data columns represent significant
differences (P < 0.001). For each sealer type, a horizontal bar
above the respective columns for the two immersion protocols
indicates no statistical difference (P > 0.05).
Dislocation resistance of ProRoot Endo Sealer Huffman et al.
International Endodontic Journal, 42, 34–46, 2009 ª 2009 International Endodontic Journal40
the tendency to flow during testing generates results
that are susceptible to erroneous interpretation. Unless
the rheological properties of the materials being com-
pressed are equivalent (Kohyama et al. 2003, Tornqvist
et al. 2004), statistical comparison of the results
derived from two thermoplastic root filling materials
is virtually meaningless. This could also have been
responsible, in part, for the recent report that sealers
tested in thin films using the thin-slice push-out test
were considerably weaker than when the same sealer
Failure modes of push out tests
Before immersionin SBF
PulpCanalSealer
AH PlusJet
ProRootEndoSealer
61.7%38.3%
20%
80%
6.7%
36.6%
56.7%74.1%
8.6%17.3%
100% 95%
5%
After immersion in SBFfor 4 weeks
Adhesive Mixed Cohesive
Figure 4 Distribution of adhesive, mixed
and cohesive failures of the three sealers
in specimens that were tested without
immersion in simulated body fluid (SBF)
and specimens that were tested after
immersion in SBF for 4 weeks.
Figure 5 Scanning electron microscopy (SEM) of AH Plus after immersion in simulated body fluid (SBF) and push-out testing. (a)
Low magnification SEM of a cohesive failure mode exhibited by a specimen from the AH Plus Jet group after SBF immersion. (b) A
higher magnification view showing the presence of large, multi-facet fillers (open arrowheads) that are characteristic of the AH
Plus sealer. These fillers were embedded in a resinous matrix together with other fine filler particles.
Huffman et al. Dislocation resistance of ProRoot Endo Sealer
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 34–46, 2009 41
was tested in bulk by eliminating the thermoplastic
core material from the canal space (Jainaen et al.
2007). The important results generated by those
authors provided incontestable substantiation that the
so-called ‘push-out bond strength’ produced by the
conventional thin-slice push-out test is not a material
property. It is prudent to emphasize that the mechan-
ical and physical properties of engineering and bioma-
terials such as flexural strength, fracture toughness or
melting point should exhibit a consistent range of
values under identical testing conditions (Callister
1994).
To minimize the shortcoming of applying a com-
pression stress over a compliant material, the largest
plunger that corresponds to the size of the thermoplas-
tic root filling material is usually selected for the thin-
slice push-out test (Gesi et al. 2005, Bouillaguet et al.
2007) Whilst this is a legitimate compromise, the
procedure succinctly requires the use of different
diameter plungers for different depths of a tapered root
canal. As the contact surface areas of the plungers are
different, data generated from different parts of the
canal walls are nonstandardized. Thus, it is futile to
statistically compare the results generated by a con-
ventional thin-slice push-out test from the coronal
third, versus those generated from the middle and
apical thirds of the canal walls.
The third limitation involves the testing of root
fillings that comprise multiple, nonuniform interfaces.
Whilst the uneven distribution of stress fields around
Figure 6 Scanning electron microscopy (SEM) of ProRoot Endo Sealer after immersion in simulated body fluid (SBF) and push-out
testing. (a) Low magnification SEM of a mixed failure mode exhibited by a specimen from the ProRoot Endo Sealer group after SBF
immersion. Sealer remnants (pointer) could be seen on part of the wall. The remaining part of the walls was devoid of sealer
remnants and appeared comparatively smooth (arrow). (b) A higher magnification view of the sealer remnants, showing the
presence of spherical bodies on sealer surface. These spherical bodies were previously shown to be amorphous calcium phosphate-
like spheres that were formed by the reaction of calcium hydroxide released by the calcium silicate with the phosphate ions present
in the SBF. (c) A very high magnification view showing that some of the amorphous calcium phosphate-like spheres (arrow) were
spontaneously transformed into apatite-like clusters along the surface of those spheres (pointer). (d) A close-up view of a spherical
apatite-like cluster showing the presence of individual apatite-like crystallites (open arrowheads).
Dislocation resistance of ProRoot Endo Sealer Huffman et al.
International Endodontic Journal, 42, 34–46, 2009 ª 2009 International Endodontic Journal42
interfaces with variable circumferential thickness can-
not be over-emphasized (Shirazi-Adl & Forcione 1992,
Mequid & Zhu 1995), the uncertainty with respect to
which interface was consistently dislodged imposes
rigorous challenges when specific hypotheses such as
the dislocation resistance of sealers from radicular
dentine are to be tested.
The fourth limitation is that one is almost certain to
find noninstrumented areas that co-exist with instru-
mented areas in an oval-shaped canal that has been
cleaned and shaped (Peters 2004). For the noninstru-
mented areas that are treated with sodium hypochlorite
as an irrigant, one should expect increases in both
undercut retention and surface contact areas within
the calcospherite-containing regions (Wakabayashi
et al. 1993, Tatsuta et al. 1999) that inadvertently
augments the dislocation resistance of the sealer being
investigated. For example, comparing the results gen-
erated from a natural canal space with 50% noninstr-
umented canal walls versus one that has 20%
noninstrumented canal walls may result in erroneous
conclusions on the dislocation resistance of various
sealers from radicular dentine. It is unrealistic to
quantify the extent of noninstrumented natural canal
walls from a root slab either before or after a push-out
test. Because of these limitations, a modified push-out
strength testing design was utilized in the present
study.
Even without SBF immersion, the calcium silicate-
based sealer was approximately 16 times as difficult to
be dislodged from the radicular dentine walls as Pulp
Canal Sealer, and almost four times as resistant to
dislodging as AH Plus Jet. This may be due, in part, to
the hardness of the calcium silicate-based sealer after
setting in the presence of 100% relative humidity. As
natural root canals cannot be completely dehydrated
(Amyra et al. 2000, Hosoya et al. 2000) due to the
retention of moisture within the dentinal tubules,
similar hardness should be expected of the set sealer
when it is used for filling natural canals. The tenacity
of this sealer to radicular dentine cannot be solely
attributed to sealer penetration into the dentinal
tubules following depletion of the smear layer, as the
dentine from the apical third of the roots is often highly
sclerotic. It is beyond the scope of this study to provide
definitive annotations on whether the increased dislo-
cation resistance is caused by the frictional resistance
or micromechanical/chemical adhesion of the sealer to
dentine (Shirazi-Adl 1992, Goracci et al. 2005). This
issue should be further investigated in the future using
more advanced transmission electron microscopy and
chemoanalytical techniques. Nevertheless, the
increased dislocation resistance of the calcium
silicate-based sealer to radicular dentine should be
advantageous in maintaining the integrity of the
sealer–dentine interface during tooth flexure, as well
as during the preparation of postholes within the filled
canal spaces.
The concern on whether the dislocation resistance of
root canal sealers is adversely affected by the contam-
ination of body fluids was simulated in the present
study by immersing the specimens in a SBF. This is an
exaggerated simulation as the entire tooth slab was
immersed in the SBF after the cavities were filled with
sealers. The increase in dislocation resistance of the AH
Plus Jet is probably caused by swelling of the epoxy
resin component after water sorption (Fernandez-Gar-
cıa & Chiang 2002, Domotor & Hentschke 2004). For
the calcium silicate-based sealer, continuous matura-
tion of the material (Andriamanantsilavo & Amziane
2004) may also have increased the material’s disloca-
tion resistance. However, the occurrence of spherical
phases along the sealer–dentine interface and within
the remnant fractured sealer after the specimens were
immersed in the phosphate-containing SBF is notable.
These spherical phases have previously been identified
as amorphous calcium phosphate when Portland
cement was immersed in a phosphate-containing fluid
(Tay et al. 2007). Amorphous calcium phosphate
phases undergo spontaneous transformation to car-
bonated apatites (Gadaleta et al. 1996), producing
hollow spherules of apatite clusters (Eanes 2001, Tay
& Pashley 2008) that contributed to the ex vivo
bioactivity of calcium silicate-containing materials
when they interact with phosphate ions. Similar
apatite-containing clusters had been observed when
Mineral Trioxide Aggregate was immersed in phos-
phate-containing fluids (Sarkar et al. 2005). The apat-
itic composition in these spherules has also been
established using x-ray diffraction (XRD) and Fourier
transform-infrared spectroscopy (FT-IR) (Tay et al.
2007). No attempt was made to analyse the compar-
atively smooth spherical phases and the crystallite-
containing spherules in this study, as these phases were
present adjacent to calcium-phosphate rich dentine and
on the surface of the fractured sealer. The use of energy
dispersive X-ray analysis to analyse these surface
phases would have yielded information that includes
the subsurface elemental composition of the dentine
and sealer components. Likewise, these phases were not
amendable for collection and purification for XRD and
FT-IR analyses. Thus, they are only referred to as
Huffman et al. Dislocation resistance of ProRoot Endo Sealer
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 34–46, 2009 43
amorphous calcium phosphate-like and apatite-like in
the present study. Generation of these reaction phases
only in specimens that were immersed in the SBF could
also have resulted in the increase in frictional resis-
tance of the sealer–dentin interface. Although it is
presumptuous to correlate the ‘in vitro bioactivity’ (i.e.
the ability to form carbonate hydroxyapatite on the
surface of a biomaterial when it is exposed to SBF)
(LeGeros 2002, Zhao et al. 2005, Panzavolta et al.
2008) observed in the present study with ‘clinical
bioactivity’ (i.e. the property of the material to develop
a direct, adherent and strong bonding with the bone
tissue) (Hench et al. 1978, Hench 1994), the issue of
‘clinical bioactivity’ associated with the use of endo-
dontic sealers in general is of practical clinical interest
and should be duly investigated.
Conclusion
Within the limits of the modified push-out testing
design utilized in the present ex vivo study, it may be
concluded that:
• Under identical cleaning and shaping conditions,
the dislocation resistance of ProRoot Endo Sealer, AH
Plus Jet and Pulp Canal Sealer are independent of the
location of the radicular dentine.
• The dislocation resistance of the three sealers are in
descending order: ProRoot Endo Sealer, AH Plus Jet and
Pulp Canal Sealer.
• Both ProRoot Endo Sealer and AH Plus Jet exhibited
higher dislocation resistance after immersion in a SBF.
• ProRoot Endo Sealer exhibited amorphous calcium
phosphate-like phases that spontaneously transformed
into apatite-like phases after immersion in the phos-
phate-containing SBF. This phenomenon probably
accounts for the in vitro bioactivity of this calcium
silicate-based sealer.
Acknowledgements
This study was supported by Dentsply Tulsa Dental
Specialties. Dr Primus and Dr Gutmann served as
consultants for Dentsply Tulsa Dental Specialties. The
authors are grateful to Miss Anna Lam for her
secretarial support.
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Influence of post fit and post length on fractureresistance
L. Buttel, G. Krastl, H. Lorch, M. Naumann, N. U. Zitzmann & R. WeigerDepartment of Periodontology, Endodontology and Cariology, School of Dentistry, University of Basel, Basel, Switzerland
Abstract
Buttel L, Krastl G, Lorch H, Naumann M, Zitzmann NU,
Weiger R. Influence of post fit and post length on fracture
resistance. International Endodontic Journal, 42, 47–53, 2009.
Aim To investigate (i) the impact of post fit (form-
congruence) and (ii) the influence of post length on the
fracture resistance of severely damaged root filled
extracted teeth.
Methodology Ninety-six single-rooted human
teeth were root filled and divided into four groups
(n = 24 per group). Post spaces were prepared with a
depth of 6 mm (group 1, 3) and 3 mm (group 2, 4).
Form-congruence with a maximal fit of the post
within the root canal space was obtained in groups 1
and 2, whereas there was no form-congruence in
groups 3 and 4. In all groups, glass fibre reinforced
composite (FRC) posts were adhesively cemented and
direct composite crown build-ups were fabricated
without a ferrule. After thermo-mechanical loading
(1200000·, 5–50 �C), static load was applied until
failure. Loads-to-failure [in N] were compared
amongst the groups.
Results Post fit did not have a significant influence on
fracture resistance, irrespective of the post length. Both
groups with post insertion depths of 6 mm resulted in
significantly higher mean failure loads (group 1, 394 N;
group 3, 408 N) than the groups with post space
preparation of 3 mm (group 2, 275 N; group 4, 237 N).
Conclusions Within the limitations of this study,
the fracture resistance of teeth restored with FRC posts
and direct resin composite crowns without ferrules was
not influenced by post fit within the root canal. These
results imply that excessive post space preparation
aimed at producing an optimal circumferential post fit
is not required to improve fracture resistance of roots.
Keywords: endodontic post, form-congruence, frac-
ture resistance, in vitro study, post space.
Received 20 May 2008; accepted 22 September 2008
Introduction
As root filled teeth often have insufficient coronal tooth
structure, placement of a post is occasionally necessary
to provide adequate retention for the core and final
restoration. Alternatives to cast post-and-cores have
been developed and include the use of pre-fabricated
posts and custom-made cores with composite that
facilitate a chair-side restorative procedure (Heydecke
et al. 2002). In particular, fibre-reinforced composite
(FRC) posts luted with adhesive materials have become
more popular because of their favourable mechanical
and aesthetic properties. For example, the elastic
modulus of FRC posts is close to that of dentine, and
results in the stress transmitted by a fibre post to the
root dentine being lower than that caused by other
materials such as titanium or zirconia (Duret et al.
1990). There is a controversy as to whether stress
transmission and post rigidity has an impact on the
fracture resistance and/or failure mode of root filled
teeth with posts (Isidor et al. 1996, Akkayan & Gulmez
2002, Fokkinga et al. 2004). In addition to the
presence of a post, other factors possibly influencing
the load capability of root filled teeth are tooth
morphology, restorative techniques and crucially the
amount of tooth tissue lost (Trope et al. 1985, Gut-
mann 1992, Sornkul & Stannard 1992, Fernandes &
Dessai 2001).
Correspondence: Leonard Buttel, Department of Periodontol-
ogy, Endodontology and Cariology, School of Dentistry,
University of Basel, Hebelstrasse 3, CH-4056 Basel, Switzer-
land (Tel.: +41 61 2672623; fax: +41 61 2672659; e-mail:
doi:10.1111/j.1365-2591.2008.01492.x
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 47–53, 2009 47
When placing posts in accordance with standard
clinical protocols, pilot drills are used to create a form-
congruent root canal up to the apical third of the root
to ensure primary post fit and retention. This optimized
post fit can be termed ‘form-congruence’ (Schmage
et al. 2005) and aims to create maximal adaptation of
the post to the surrounding root canal walls with a
thin and even post dentine cement interface. It is
believed that form-congruence facilitates stress distri-
bution along the canal wall during clinical function
(Morgano 1996). Schmage et al. (2005) examined the
form-congruence of five pre-fabricated titanium posts
luted with zinc phosphate cement and found that the
mean cement gap varied between 33 and 62 lm,
depending on the post system. For root filled teeth with
cast post-and-cores and crowns luted with zinc phos-
phate cement, a significant increase in fracture resis-
tance was reported when a maximum adaptation of a
tapered post to the residual root structure was present
(Sorensen & Engelman 1990). This effect was not
observed when parallel-sided posts were used. Prepar-
ing post spaces, however, poses several risks. The
individual curvature and cross-section of the root
canal may interfere with this preparation and create
additional weakening of the root or even root perfo-
ration. Lang et al. (2006) investigated the impact of
endodontic procedures on the deformation of anterior
maxillary teeth and found that their stability decreases
with every stage of the root canal preparation.
A significant decrease in stability was observed when
the post space was prepared, particularly following the
transformation of the conical post preparations to a
cylindrical form. It was concluded that if excessive
amounts of tooth structure are removed and the
natural geometry of the root canals are altered, this
will have a destabilizing effect on root filled teeth.
A recent study using computational, experimental and
fractographic analyses has substantiated the impact of
so called inner dentine located adjacent to the root
canal on fracture resistance of teeth (Kishen et al.
2004). Obviously, it is not only the thickness of the
dentine wall that stabilizes the root but also the
presence of inner dentine with a lower elastic modulus
than the more mineralized outer dentine. Particularly
in irregular root canals with an oval cross-section,
large diameter drills are required to ensure a circum-
ferential post fit, and thereby excessive amounts of
inner dentine are removed. Selecting a post that
corresponds best to the natural root canal diameter
without preparation, however, aims to preserve the
inner dentine substance and may be associated with a
loose-fitting post in irregular canals (no form-congru-
ence).
As soon as posts are luted adhesively to the root
canal walls, an ideal post fit within the canal (form-
congruence) is probably less important as any spaces
are filled with the luting composite. However, shrink-
age of the thicker resin cement film by nonfitting posts
may impair the clinical performance in the long term.
Otherwise, even after standardized post space prepara-
tion (using the post hole drills supplied by the
manufacturers) and optimal bonding procedures, the
high-cavityconfiguration factor may lead to gap
formation either along the cement-dentine interface
or the cement-post interface (Pirani et al. 2005). To
reduce the thickness of resin cement in irregular post
spaces, Grandini et al. (2003, 2005) suggested a
pre-cementation relining of the post with flowable
composite (anatomical post) for the cementation of fibre
posts to improve its fit to the canal space. In the light of
this background, the use of adhesive techniques for post
cementation and a minimal invasive post space prep-
aration minimizing the loss of hard tissue are clinically
preferable.
The aim of the present investigation was to study the
influence of the form-congruence of adhesively luted
glass FRC posts and of post length on the fracture
resistance of root filled teeth. The null hypothesis was
that (i) providing a form-congruence between post and
post space preparation and/or (ii) reducing the post
length would have no influence on the fracture load of
root filled teeth restored with adhesively luted glass FRC
posts and direct composite crowns.
Materials and methods
Ninety-six extracted single-rooted human teeth (max-
illary lateral incisors and mandibular second premo-
lars) were selected that fulfilled the following criteria:
straight, sound roots, completely formed apices,
absence of root caries and no visible fracture lines
along the root. Teeth with similar dimensions at the
cementoenamel junction (CEJ) in terms of root diameter
and thickness of the dentine wall were distributed
equally amongst the four groups. The teeth were stored
in 0.1% thymol solution until further processing. The
clinical crowns were removed 1 mm below the buccal
CEJ using a diamond bur, leaving a root length of
13 ± 1 mm. All roots were cleaned with scalers.
Root canal preparation was performed using NiTi
rotary instruments (Race, FKG, La Chaux-de-Fonds,
Switzerland) under intermittent rinsing with 1%
Form-congruence of endodontic posts Buttel et al.
International Endodontic Journal, 42, 47–53, 2009 ª 2009 International Endodontic Journal48
sodium hypochlorite to an apical size 45. The canals
were then dried with paper points and filled with
vertically compacted gutta-percha (Obtura II, Obtura
Corp, Fenton, MO, USA) using an epoxy sealer (AH
plus, Dentsply De Trey, Konstanz, Germany).
For each group, pre-fabricated glass FRC posts (FRC
Postec, Ivoclar Vivadent, Schaan, Liechtenstein) with a
9.3% taper were used. Post spaces were prepared using
appropriate drills with the same taper in a slow-speed
contra-angle handpiece at 1000 rpm. For the 3 mm
post length (group 2 and 4), the apical 3 mm of the
post was cut off to obtain similar dimensions of the post
diameter in the cervical region of all specimens (Fig. 1).
In groups 1 and 2, the size and shape of the bur
corresponded to the FRC post to ensure optimal post fit
(form congruence between post and post space). In
groups 3 and 4, a more extensive post space prepara-
tion was created to simulate missing form-congruence
between post and post space. For that reason, the pilot
drill was shortened by 3 mm apically (group 2) and
6 mm (group 4). Because of the conical shape of the
drill, the diameter of the post space preparation
increases by about 300 lm along the whole length.
This discrepancy between post space and post diameter
results theoretically in a circumferential space width of
150 lm provided that the post is centered in the post
space. The coronal part of the post was reduced in each
group at the same level, i.e. 2.5 mm above the root
canal orifice.
Restorative procedures
Prior to post cementation, the post space was rinsed
with water for 30 s and dried with an air blow for 5 s
and with paper points. Subsequently, all dentine
surfaces were etched with one step (Ultra-etch, 35%
phosphoric acid) for 15 s, rinsed with water spray for
15 s and dried carefully with an air stream for 5 s and
with paper points, leaving the surface slightly moist.
A dual-cure adhesive system (Excite DSC, Ivoclar
Vivadent) was mixed and applied to the sample surface
for 30 s. A gentle air stream was used to evaporate the
dissolution fluid. The FRC posts were cleaned with
alcohol and silanated (Monobond-S, Ivoclar Vivadent)
for 60 s. A dual-curing resin luting material (Multicore
Flow, Ivoclar Vivadent) was mixed and injected into the
prepared root canal with an appropriate tip (C-R
NeedleTubes, Centrix, Shelton, CT, USA). Subsequently,
the post was seated using finger pressure for 10 s.
Excess cement was spread with a brush in a thin layer
Figure 1 Schematic drawing of the post space preparation and the fibre reinforced composite post in the four groups.
Buttel et al. Form-congruence of endodontic posts
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 47–53, 2009 49
so that it covered the occlusal surface of the specimens.
The cement was light-cured (Optilux 500, Demetron/
Kerr, Danbury, CT, USA) for 40 s in an occlusal
direction.
To restore the coronal part of the teeth, direct
composite crowns were built up with the same material
(Multicore Flow). Despite slight differences in the
cervical diameter of the roots, standardized crowns
(4 mm height) were fabricated using transparent
moulds (Pella crowns, Odus, Dietikon, Switzerland)
with anatomically formed occlusal surfaces. Composite
resin was placed free of bubbles in the mould, adapted
to the tooth surface and then light-cured from each side
for 40 s. Finally, the excess composite resin in the
cervical area was removed and the margins of the
restoration were finished using fine diamond burs. In
each specimen, the tip of the post was covered with a
layer of resin composite approximately 1.5 mm in
height.
Mechanical loading
The roots of all specimens were coated with an air-
thinned 0.3-mm layer of polyvinylsiloxane (President
light body, Coltene-Whaledent AG, Altstatten, Switzer-
land) to simulate a periodontal ligament (PDL). The
specimens were fixed with a light-curing composite on
custom-made metallic holders (Provac, Balzers, Liech-
tenstein). The roots were then embedded in self-curing
acrylic resin (Demotec 20, Demotec Siegfried Demel,
Nidderau, Germany) so that the CEJ was situated
approximately 1.5 mm above the simulated bone level
(i.e. the upper margin of the embedding medium). After
embedding, the samples were stored in water until
loading.
All specimens were loaded mechanically at the
centre of the occlusal surface using a computer-
controlled masticator (CoCoM 2, PPK, Zurich, Switzer-
land). Stressing comprised 1.2 million occlusal loads of
49 N at 1.7 Hz obtained by using human cusps.
Simultaneously, thermal stress was applied (3000
thermal cycles between 5/50 �C). These conditions
are believed to simulate approximately 5 years of
clinical service (Krejci et al. 1994).
After thermo-mechanical loading (TML), the fracture
resistance was tested using a universal testing machine
(Zwick, Ulm, Germany). Specimens were fixed in a
metal holder with the long-axis of the roots at an angle
of 45� to the load direction. A tin foil (0.5-mm thick)
was placed between the steel sphere and the crown to
avoid load peaks on the composite resin crown surface.
The linear compressive load was applied (cross-head
speed = 0.5 mm min)1) at the central fissure of the
occlusal surface in the direction of the buccal cusp until
failure.
Statistical analysis
Primary outcome variable was failure during TML
(fatigue testing). Second, loads-to-failure (in N) were
compared when the specimens survived TML. There-
fore, mean values and confidence intervals were
calculated for the nonfailing specimens of each group.
A significant difference between two groups is given
when the confidence intervals do not overlap.
Results
Two specimens, one in group 2 and one in group 4,
were lost because of failures in technical handling. All
remaining teeth and restorations survived TML without
loss of retention or visible fractures and were further
tested for fracture resistance in the universal testing
machine. Mean fracture loads after static loading are
given in Table 1. There was no statistical significant
difference between specimens with 6 mm post length
without form-congruence (group 3) and group 1
(6 mm, form-congruence). Significantly, lower values
were recorded for specimens with a 3-mm short post
(groups 2 and 4). The lowest load values were
Table 1 Failure loads in the four groups
Group n Mean failure load (N) SD (N)
95% Confidence interval for mean
failure load (N)
Lower bound Upper bound
1 (6 mm, form-congruence) 24 393.99A 98.89 352.23 435.75
2 (3 mm, form-congruence) 23 275.47B 75.61 242.77 308.16
3 (6 mm, no form-congruence) 24 408.06A 130.20 353.08 463.04
4 (3 mm, no form-congruence) 23 236.74B 96.27 195.11 278.37
Values exhibiting the same subscript number indicate no significant difference between the groups.
Form-congruence of endodontic posts Buttel et al.
International Endodontic Journal, 42, 47–53, 2009 ª 2009 International Endodontic Journal50
registered in group 4. In the current experimental set-
up, form-congruence had no impact on fracture resis-
tance, irrespective of the post insertion depth.
Discussion
The present study was conducted to evaluate the
influence of form-congruence between post and post
space as well as reduced post length in severely
damaged root filled teeth. It was observed that post fit
did not have a significant impact on fracture resistance,
whilst short post length decreased load values signifi-
cantly, meaning that they fractured more easily.
To gain information about the potential need for a
maximum adaptation of the post to the canal wall, a
lack of form-congruence was created in the current
material by cementing a post in an over-enlarged root
canal. The resulting gap was filled with flowable resin,
which was concurrently used for the crown build-up to
simplify the procedure. This is in accordance with a
recent study suggesting that such materials lead to
better retention than luting cement and therefore
recommending them as alternatives for post cementa-
tion (Ohlmann et al. 2008). The results of the present
study using resin cement clearly demonstrated that
missing form congruence did not impair fracture loads.
In contrast to these findings, Schmage et al. (2005)
reported that only a post closely adapted to the root
canal wall resulted in high retention and prevented
stress peaks. They applied conventional luting material
(zinc phosphate cement) and found that a thin homo-
geneous cement layer, where the film thickness was
<50 lm, was essential to improve post retention.
However, when the composite was used as a luting
material, a mismatch between the diameter of the post
space and that of the post did not impair retention
(Assif & Bleicher 1986, Hagge et al. 2002), even when
shrinkage of the thicker resin cement film resulted in
more stress at the interface between the dentine and
the post (Alster et al. 1997). Perez et al. (2006)
investigated the impact of the resin cement thickness
on the bond strength to the root canal dentine.
Obviously, increased cement thickness did not reduce
the bond strength significantly when FRC posts were
inserted. These findings are in line with those of a
recent study demonstrating that the accuracy of fit
between post and root canal did not influence bond
strength (Perdigao et al. 2007).
With the exception of the two technical failures, in
the current experiment, all the teeth and restorations
survived without loss of post retention or crown
fracture. When loaded to failure, fracture loads in all
groups were found to exceed the chewing forces
normally associated with adults, which ranges from 7
to15 kg (Tortopidis et al. 1998). Teeth with 6-mm deep
post preparations (groups 1 and 3) exhibited similar
failure loads regardless of whether there was form-
congruence between the post and the root canal.
Specimens restored with 3 mm post length with or
without form-congruence (groups 2 and 4) yielded
significantly lower values. Again, the form-congruence
of the FRC-posts had no influence on the load capability
of root filled teeth. During the last decade, the use of
resin composite for direct crowns in root filled teeth has
been recommended only for temporary restorations.
Laboratory investigations of the fracture resistance of
resin composite crowns (with or without endodontic
posts) have, however, yielded promising results, which
suggest that their clinical application is appropriate
(Krejci et al. 1994, Fokkinga et al. 2005). In a 5-year
prospective clinical study on core restorations without
crowns, Creugers et al. (2005a) demonstrated that only
two out of 99 restorations failed. They found that direct
composite build-up restorations exhibited high durabil-
ity and a survival rate similar to that of crowned build-
up restorations in the parallel trial (Creugers et al.
2005b).
To mimic a human periodontium (PDL), the roots of
the tested teeth were covered with a layer of cured
polyvinylsiloxane. The presence of this simulated PDL
was found to significantly affect the results of fracture
testing (Soares et al. 2005). The extracted human teeth
used in the present study were sectioned 1 mm below
the buccal CEJ, thereby removing the enamel com-
pletely. The remaining dentine surface is deemed to
provide poorer bonding characteristics than enamel
(Van Meerbeek et al. 2003). The prepared roots were
provided with posts of different lengths and direct
composite crown build-ups, but no ferrule was
achieved. The advantage of a ferrule is that it generally
facilitates a stabilizing effect by embracing the dentine.
The tooth morphology established here, however,
simulated that of a severely damaged root filled tooth.
This situation is, according to the established clinical
guidelines (Schwartz & Robbins 2004), ideally restored
with a post and core build-up and a custom-made
laboratory crown with circular ferrule (Stankiewicz &
Wilson 2002). In most laboratory studies (Heydecke
et al. 2002, Fokkinga et al. 2006, Salameh et al. 2007),
this clinical recommendation is taken into account and
the tested specimens revealed fracture loads higher
than that in the current investigation. The ferrule
Buttel et al. Form-congruence of endodontic posts
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 47–53, 2009 51
design of crowns is generally considered to be one of the
most important factors to improve the load resistance of
root filled teeth (Sorensen & Engelman 1990, Assif et al.
1993, Isidor et al. 1999, Akkayan 2004, Naumann
et al. 2007). The present results reflect, therefore, the
performance of the post and core alone, without being
confounded by the additional value of a ferruled crown.
In the current material, TML was conducted to
fatigue the samples prior to static loading. A repeatedly
applied load in an aqueous environment simulates
clinical conditions better than static loading alone.
Using this environment, factors such as fatigue stresses
or ageing, which influence the survival of materials can
be taken into account (Naumann et al. 2005). How-
ever, the test designs of laboratory studies can only
partially reflect the clinical situation. Clinically, loading
is a dynamic process and loading forces, frequency and
direction vary greatly. Because of the large number of
other variables involved, including tooth condition,
tooth type, applied restorative procedures and restor-
ative materials used, it is almost impossible to compare
the fracture resistance values obtained in different
laboratory studies. In particular, the most unpredictable
factor is the tooth conditions, which are mainly related
to dentine (Kinney et al. 2003). This is an inherent
drawback associated with the use of human teeth. It has
been reported that testing human teeth results in a large
standard deviation (Krejci et al. 2003), whilst artificially
manufactured teeth are much more consistent (Ottl
et al. 2002). In the present study, a sample size of 24
human teeth was chosen for each group to reduce the
SD and to achieve more reliable results.
The findings of the present study strongly suggest
that excessive post space preparation to maximize post
fit and to reduce the amount of resin cement is not
necessarily required. These results are particularly
encouraging for teeth with oval or long oval root canal
cross-sections. In such cases, not attempting to achieve
a good circumferential post fit helps to preserve inner
dentine and avoids additional weakening of the root.
Further investigations should be conducted to study the
effect of more oval pre-fabricated posts on the load
capability.
Conclusions
Severely damaged root filled teeth restored with FRC
posts and direct resin composite crowns without a
ferrule revealed similar fracture resistance irrespective
of the fit of the post, i.e. irrespective of form-congruence
or no form-congruence. This suggests that post space
preparation and a fitting post are not required to
improve fracture resistance.
Acknowledgements
The authors gratefully acknowledge the Swiss Society
of Odontology (SSO Kuratorium, research project no.
220) for the generous financial support. The authors
would also like to thank Svend Galli, dental technician
and Andres Izquierdo for their valuable help.
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Buttel et al. Form-congruence of endodontic posts
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 47–53, 2009 53
Root canal morphology of mandibular firstpremolars in an Indian population: a laboratorystudy
N. Velmurugan & R. SandhyaDepartment of Conservative Dentistry & Endodontics, Meenakshi Ammal Dental College & Hospital, Chennai, Tamil Nadu, India
Abstract
Velmurugan N, Sandhya R. Root canal morphology of
mandibular first premolars in an Indian population: a laboratory
study. International Endodontic Journal, 42, 54–58, 2009.
Aim To determine the root canal morphology of
mandibular first premolar teeth in an Indian popula-
tion using a decalcification and clearing technique.
Methodology One hundred extracted adult mandib-
ular first premolar teeth were studied following decalci-
fication and clearing. The shape of the canal orifice, root
canal pattern and length of the teeth were determined.
Results The mandibular first premolars were identi-
fied to have a round orifice (38%), oval orifice (44%),
flattened orifice (17%) and C-shaped orifice (1%). The
canal patterns were classified as Type I (72%), Type II
(6%), Type III (3%), Type IV (10%) and Type V (8%)
according to Vertucci’s classification. C-shaped canals
were identified in one tooth (1%). The average length of
the teeth was 21.6 mm. Fourteen per cent of the teeth
had mesial invaginations of the root.
Conclusions Type I canal patterns were the most
frequently occurring in mandibular first premolars
amongst the Indian population. 85.7% of the teeth
with mesial invagination of the root had either two
canals or division of canals.
Keywords: canal orifice, decalcification and clear-
ing, length of the teeth, mandibular first premolar,
mesial invagination.
Received 7 March 2008; accepted 29 September 2008
Introduction
Understanding root canal morphology and its com-
plexity is essential during endodontic therapy. Varia-
tion in the morphology of root canal systems occurs
commonly and can be considered as normal (Cohen &
Hargreaves 2006). Amongst the human permanent
dentition, Brescia (1961) reported that the mandibular
first premolar teeth had the most variable canal
pattern. A study at the University of Washington
assessed the failure rate of nonsurgical root canal
therapy in all teeth. The mandibular first premolar had
the highest failure rate and this may be attributed to
the frequent variations in the root canal morphology
and the inability to access extra canals (Ingle & Taintor
1985).
It is a well known fact that the root canal system
varies with race (Trope et al. 1986, Ahmed et al.
2007), and gender (Sert & Bayirli 2004). Earlier studies
on root canal systems were completed most commonly
on teeth from Caucasian populations. Similar studies
amongst the Indian population are rare (Reuben et al.
2008). The aim of this study was to determine the root
canal morphology of mandibular first premolar teeth in
an Indian population using a decalcification and
clearing method.
Materials and methods
One hundred extracted human adult mandibular first
premolar teeth from an Indian population were col-
lected. The age and gender of the patients were not
known. Teeth with deep caries, metallic restorations,
Correspondence: Dr N. Velmurugan, # 2, 95th Street, 21st
Avenue, Ashok Nagar, Chennai 600083, Tamil Nadu, India
(Tel.: 9840164167; fax: 044 2378 1631; e-mail: vel9911
@yahoo.com).
doi:10.1111/j.1365-2591.2008.01494.x
International Endodontic Journal, 42, 54–58, 2009 ª 2009 International Endodontic Journal54
fracture, incompletely formed roots and those which
were root filled were not included. Handling of the teeth
was carried out according to Occupational Safety and
Health Administration guidelines and regulations.
The teeth were preserved in 10% formalin (Western
India Chemical, Udupi District, Karnataka, India). All
attached soft tissue and calculus were removed using
an ultrasonic scaler. The length of the teeth was
measured using vernier caliper from the tip of the
crown to the apex of the root. In case of a curved root,
tangents were drawn to the curved portions of the
tooth. The length was then measured by connecting
the points of tangency.
The teeth were decalcified and rendered transparent
using the technique reported by Robertson et al. (1980)
to obtain a 3D view of the root canal system. Access
cavities were prepared using a round bur (No. 2 round
bur) and the shape of the canal orifice was observed
with the naked eye. Following this, the teeth were
placed in 3% sodium hypochlorite (Merck Limited,
Mumbai, Maharashtra, India) for 48 h. The teeth were
agitated manually to ensure complete removal of the
pulp tissue. The teeth were then washed in running
water for 2 h and then transferred to 5% nitric acid
(Merck Limited) for decalcification. The teeth were
placed in acid for 72 h, with the acid being changed
every 24 h and stirred once every 8 h. The end-point of
decalcification was determined by taking a radiograph
of three sample teeth, which showed uniform decalci-
fication of the teeth. The teeth were then washed in
running water and dehydrated using ascending grades
(70%, 80%, 90% and 100%) of isopropyl alcohol
(Leonid Chemicals Pvt Ltd, Bangalore, Karnataka,
India) for 2 days. Finally, they were rendered trans-
parent by immersion in methyl salicylate (Sipali
Chemicals, Chennai, Tamilnadu, India) and an oil-
based dye was injected into the access cavity. The
anatomy of the root canal was observed and classified
based on the Vertucci’s classification (Vertucci 1984).
The supplementary canals present at the apical third
were grouped as accessory canals and those in the
middle third as lateral canals. Fourteen teeth in the
study had invagination of the root surface on its mesial
aspect. These teeth were analysed to check for any
specific variations of the canal anatomy that could be
associated with this feature.
Results
Canal orifice
The shape of the canal orifices were round in 38% of
the teeth, oval in 44% of the teeth, flattened ribbon
shaped in 17% of the teeth and C-shaped in 1% of the
teeth. Two canal orifices were seen in 2% of the teeth.
Canal type
Amongst the 100 mandibular first premolar teeth,
72% had a Type I canal pattern (Fig. 1a) with Type II,
Type III, Type IV and Type V canals being identified in
6%, 3%, 10% and 8% of the teeth respectively
(Fig. 1b–e, Table 1). One tooth had Category III
c-shaped canal (1%) (Melton et al. 1991). Lateral
canals were observed in 4% of the samples and
another 4% of the samples had accessory canals.
Intercanal communication was identified in only one
tooth sample (1%).
Position of the apical foramen
Amongst the teeth with a single canal at the apex
(n = 82), the apical foramen was located at the apex of
the root in 83% teeth, 0.5 mm from the apex in 6%
a) (b) (c) (d) (e)
Figure 1 Various canal patterns in mandibular first premolars. (a) Type I, (b) Type II, (c) Type III, (d) Type IV, (e) Type V.
Velmurugan & Sandhya Root canal morphology
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 54–58, 2009 55
teeth, 1 mm from the apex in 9.7% teeth and 2 mm
from the apex in 1.2% teeth.
Length of teeth
The longest tooth in this study was 25.2 mm and the
shortest was 17.7 mm. The average length of the
mandibular first premolar teeth was 21.6 mm, the
median and mode were 21.3 mm.
Mesial invagination of the teeth
Mesial invagination of the root was found in 14% of the
teeth. Amongst them, 7 teeth had Type IV canal
pattern; 3 had Type V canal pattern and 2 had Type I
canal pattern (Fig. 2 Table 2). One tooth with Type II
and one tooth with Type III canal pattern were also
identified. 85.7% of the teeth with mesial invagination
had either two canals or division of canals. The mean
distance from the cusp tip to the point of initiation of
invagination was 14.6 mm.
Discussion
This study analysed the canal morphology of mandib-
ular first premolar teeth amongst an Indian population
using a decalcification and clearing technique. Previous
studies report a high occurrence of Type I canal pattern
(Vertucci 1984). Studies on root canal anatomy have
Table 1 Pattern and percentage of canals
Type of
canal
Canal
pattern
% of
Occurrence
(n = 100)
Type Ia 1 72
Type IIa 2-1 6
Type IIIa 1-2-1 3
Type IVa 2 10
Type Va 1-2 8
Type VIa 2-1-2 0
Type VIIa 1-2-1-2 0
Type VIIIa 3 0
Cb 1-3-1 1
aVertucci (1984).bMelton et al. (1991).
(a)
(a1)
(b)
(b1)
(c)
(c1)
Figure 2 Mandibular first premolars with mesial invagination of the root (a, b, c) and their root canal patterns (a1, b1, c1).
Root canal morphology Velmurugan & Sandhya
International Endodontic Journal, 42, 54–58, 2009 ª 2009 International Endodontic Journal56
been conducted using methods, such as radiography
(Pineda & Kuttler 1972, Willershausen et al. 2006),
decalcification and clearing (Caliskan et al. 1995,
Rwenyonyi et al. 2007), direct observation with micro-
scope (Sempire & Hartwell 2000), 3D reconstruction
(Mikrogeorgis et al. 1999), computed tomography
(Robinson et al. 2002, Reuben et al. 2008) and mac-
roscopic sections (Baisden et al. 1992, Lu et al. 2006).
It has been mentioned that the most detailed informa-
tion can be obtained by demineralization and clearing
technique (Vertucci 1984). Moreover, it is simple,
acceptable and an inexpensive procedure (Rwenyonyi
et al. 2007).
The most prevalent canal pattern in the present
study was Type I occurring in 72% of the mandibular
first premolars (Fig. 1a, Table 1). In an earlier study
(Vertucci 1984) in Caucasian population, the preva-
lence was 70%, whereas other studies have reported a
Type I canal pattern in 67.2% to 86.3% of teeth(Zillich
& Dowson 1973, Trope et al. 1986). A Type II canal
was encountered in 6% of the samples and Type V in
8% of the samples (Fig. 1, Table 1). Vertucci (1984) did
not report any Type II canal patterns, but 24% of the
teeth in his study had a Type V canal pattern. These
variations may be attributed to the racial or genetic
factors. Vertucci (1984) reported the occurrence of
C-shaped canal in 0.5% of the samples, whereas in the
present study, it was identified in one tooth (1%)
(Table 1). Melton et al. (1991) classified C-shaped
canals into three types. The C-shaped canal identified
in this study was Category III sub division I, where the
canal divided into three in the middle third and
reunited at the apical region to exit through one
foramen.
A previous study reported the average length of
mandibular first premolar teeth to be 21.6 mm (Cohen
& Hargreaves 2006). The average length of the teeth in
the present study was also found to be 21.6 mm. In this
study there were 14 teeth with a mesial invagination of
the root. The point of initiation and the depth of the
invagination varied. According to Ash (1999), these
are deep developmental grooves found on the mesial
surface of the root. Radiographic studies on canal
anatomy have not reported on mesial invaginations of
roots as it is impossible to identify its presence in
clinical radiographs. The only in vivo study that
reported their occurrence using spiral computed
tomography concluded that 15% of mandibular pre-
molars had invagination (Robinson et al. 2002).
According to that study, the mesial invagination gave
a false radiographic line that one can mistake for an
extra canal. In this study, amongst the 14 teeth having
mesial invagination of the root, 8 teeth had two canals,
4 teeth had bifurcation of canal and 2 teeth had a
single canal. The teeth with two canals (Type II and
Type IV) had the mesial invagination initiating from
the cervical half of the tooth root. The teeth with canal
bifurcation (Type III and Type V) and single canal
(Type I) had the invagination in the apical half of the
root, with the single canal specimen having the
invagination apically. In these teeth, the lingual canal
after bifurcation was smaller in diameter when com-
pared with the buccal canal. The location of the canal
bifurcation varied in accordance with the location of
the point of initiation of invagination. There seems to
be some anatomical correlation between mesial invag-
ination of the root and canal pattern which requires
further analysis.
Conclusion
A Type I canal pattern was found to be the most
prevalent in mandibular first premolar teeth amongst
this Indian population. More than one canal was
commonly found in the teeth with mesial invagination
of the root.
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Canal
type
No. of
teeth
Average point
of initiation of
invagination (mm)a
Type I 2 16.5
Type II 1 14.4
Type III 1 15.3
Type IV 7 13.8
Type V 3 15.1
aPoint of initiation of invagination measured from the cusp tip.
Average: 14.6 mm; median: 14.4 mm; mode: 15.3 mm; vari-
ance: 2.5; SD: 1.59.
Velmurugan & Sandhya Root canal morphology
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Root canal morphology Velmurugan & Sandhya
International Endodontic Journal, 42, 54–58, 2009 ª 2009 International Endodontic Journal58
Necrotic pulp tissue dissolution by passiveultrasonic irrigation in simulated accessory canals:impact of canal location and angulation
A. Al-Jadaa, F. Paque, T. Attin & M. ZehnderDepartment of Preventive Dentistry, Periodontology and Cariology, University of Zurich Center of Dental Medicine, Zurich,
Switzerland
Abstract
Al-Jadaa A, Paque F, Attin T, Zehnder M. Necrotic pulp
tissue dissolution by passive ultrasonic irrigation in simulated
accessory canals: impact of canal location and angulation.
International Endodontic Journal, 42, 59–65, 2009.
Aim To evaluate whether passive ultrasonic irrigation
(PUI) of 2.5% NaOCl would dissolve necrotic pulp tissue
from simulated accessory root canals (SACs) better
than passive placement of the irrigant, when temper-
ature was equilibrated between the two treatments.
Methodology Transparent root canal models
(n = 6) were made from epoxy resin. SACs of 0.2 mm
diameter were placed at defined angles and positions in
the mid-canal and apical area. SACs were filled with
necrotic bovine pulp tissue. PUI was performed five
times for 1 min each with irrigant replenishment after
every minute. Main canal temperature was measured
after each minute, and a digital photograph was taken.
In control experiments, mock treatments were per-
formed with the same set-up without activation of the
file using heated NaOCl to mimic the temperature
created by PUI. Experiments were repeated five times.
Digital photographs were analysed for the distance of
dissolved tissue into the SACs in mm. Overall compar-
ison (sum of dissolved tissue from all five accessory
canals) between treatments was performed using
paired t-test. Differences between SAC angulation and
position after PUI were investigated using anova/
Bonferroni (alpha < 0.05).
Results Passive ultrasonic irrigation caused a rise in
irrigant temperature in the main canal to
53.5 ± 2.7 �C after the fifth minute. PUI dissolved a
total of 6.4 ± 2.1 mm, mock treatment controlled for
heat: 1.4 ± 0.6 mm (P < 0.05). No significant influ-
ence of SAC position or angulation was found.
Conclusions Passive ultrasonic irrigation promotes
positive tissue-dissolving effects beyond a rise in
irrigant temperature.
Keywords: sodium hypochlorite, passive ultrasonic
irrigation.
Received 30 July 2008; accepted 3 October 2008
Introduction
Disinfection and debridement of root canals is an
important aspect of endodontic treatment. Based on the
fact that mechanical preparation alone cannot fully
achieve this aim (Bystrom & Sundqvist 1981), the
chemo-mechanical principle using topically applied
substances during and after instrumentation was
established. In this context, the correct choice of the
chemicals to be used and their ideal mode of application
are of interest. Sodium hypochlorite is the root canal
irrigant of choice for many practitioners, as it dissolves
necrotic tissue (Naenni et al. 2004) and has a superior
antimicrobial effect compared with most other disin-
fectants that have been used in the root canal system
(Vianna et al. 2006). It has been shown that the local
efficacy of hypochlorite preparations can be improved
Correspondence: Matthias Zehnder, PD Dr med dent PhD,
Department of Preventive Dentistry, Periodontology and
Cariology, University of Zurich Center for Dental Medicine,
Plattenstrasse 11, CH 8032 Zurich, Switzerland (Tel.:
+41 44 632 8610; fax: +41 44 634 4308; e-mail: matthias.
doi:10.1111/j.1365-2591.2008.01497.x
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 59–65, 2009 59
by heating the solution to be applied (Sirtes et al.
2005). Alternatively, the irrigant can be activated
mechanically. Amongst the mechanical methods for
irrigant activation, passive ultrasonic irrigation (PUI) is
probably the most established method (van der Sluis
et al. 2007).
Ultrasound was first introduced to endodontics in
1957 for mechanical root canal and root-end prepara-
tion (Richman 1957). Later, it was realized that
ultrasonic activation could be beneficial in enhancing
the efficacy of irrigants in the root canal (Martin 1976,
Martin & Cunningham 1985). The main effects in this
context are (transitional) cavitation and streaming
(Walmsley 1987). Both phenomena are well known to
enhance the effectiveness of antiseptics, especially
sodium hypochlorite (Martin & Cunningham 1985,
Blume & Neis 2005). Whilst streaming undoubtedly
occurs, it is unclear whether cavitation actually occurs
in the root canal system (Ahmad et al. 1987, Lumley
et al. 1988). A third, often overlooked, effect of the
application of ultrasonic energy in the root canal is the
general increase in irrigant temperature (Cunningham
et al. 1982, Cameron 1988).
Researchers have extensively studied the influence of
ultrasonic irrigant activation on the appearance of root
canal walls as observed by scanning electron micros-
copy (Ahmad et al. 1987, Abbott et al. 1991). Others
used a scoring model of the stained organic debris and
smear layer (Cheung & Stock 1993). It was found that
ultrasonic activation increases the debridement activity
of sodium hypochlorite (Cameron 1987). Using artifi-
cially prepared grooves filled with dentine debris in the
walls of human root canals as well as in artificial
canals, it has been shown that PUI has the potential to
remove debris from canal extensions and irregularities
(van der Sluis et al. 2005). It was also shown in situ
that the soft tissue debridement of sodium hypochlorite
is greatly enhanced by ultrasonic activation in the
isthmus areas of human mandibular molars (Burleson
et al. 2007). However, until now the impact of PUI on
accessory canals is still unclear because of the lack of
studies with such observations. It has been shown that
clinically, these areas are especially difficult to clean
(Nair et al. 2005). The lack of studies on irrigant action
in lateral or accessory canals can be related to the
difficulty in carrying out such investigations on natural
teeth, as the accessory canal position and status before
treatment are difficult to determine. Consequently,
there appears to be a need for standardized models
simulating accessory canals with multiple controlled
variables yielding repeatable results. The aim of this
study was to establish a model especially tailored for
this purpose.
Materials and methods
Fabrication of model
A suitable model that would allow the observation and
direct quantitative measurement of pulp tissue before
and after irrigation was not available. A transparent
model was prepared using a wax mould that was filled
with epoxy resin (Stycast, Emerson & Cuming, Wester-
lo, Belgium). To ensure reproducibility of the model, a
sheet of paper with a drawing representing the main
canal, position and angulation of accessory canals was
used as reference to assemble the parts in the proper
position using super glue before transferring them to a
box made of pink plate wax with a dimension of 30, 20
and 15 mm length, width and height, respectively
(Fig. 1a,b). The main canal was simulated using a
D-size finger spreader (Dentsply Maillefer, Ballaigues,
Switzerland). This instrument had a length of 25 mm,
a tip diameter of 0.35 mm, and a 0.06 taper (Briseno
Marroquın et al. 2001). Accessory canals were created
by 0.2-mm stainless steel wires (Fig. 1b,c). The length
of the canal was determined by allowing 5 mm of the
wire to extrude from a 22-gauge needle (Ultradent
Products, Inc. South Jordan, UT, USA), The needle was
used later to carry the necrotic pulp tissue and apply it
into the canal by means of injection. A pair of canals
were placed at distances of 1 mm and 9 mm from the
main canal apex opposing each other, one of these was
made perpendicular to the main canal, the other
created at a 45� angle with the apical extension of
the main canal. In addition, an accessory canal that
continued in the direction of the main canal (180�) was
created. A millimetric paper scale was placed parallel to
the long access of each simulated accessory canal to
ensure a precise measurement of the length of tissue
dissolution. Eight models were fabricated to be used in
the study. Before any of the models were used,
continuity of simulated accessory canals with the main
canal was ensured by introducing a 0.2-mm wire inside
each accessory canal until it appeared in the main
canal. Finally, a simulated pulp chamber and reservoir
for the passively placed irrigant was created using a
rubber tube with a length of 7 mm and 3 mm internal
diameter, which was glued over the main canal
entrance. This reservoir ensured that the whole canal
remained filled with irrigant after the passive ultrasonic
activation procedure described below. A model ready to
PUI in accessory canals Al-Jadaa et al.
International Endodontic Journal, 42, 59–65, 2009 ª 2009 International Endodontic Journal60
be filled with necrotic pulp tissue is depicted in Fig. 1,
panel d.
Bovine pulp tissue preparation
The accessory canals of seven models were filled with
bovine pulp tissue. The tissue was obtained from bovine
anterior teeth of animals that were raised and slaugh-
tered for food production according to the Swiss
standards of animal welfare. Consequently, this study
was not considered an animal study and the internal
review board had no objections to the current protocol.
Pulps were extirpated after decoronation of the teeth
and then frozen at )20 �C. Frozen tissue was thawed,
dried with paper tissues, and then each piece was
immersed in liquid nitrogen to achieve a solid dry
material. Subsequently, tissue was transformed into
fine particles using a scalpel to scratch the hard surface.
Sometimes it was required to re-immerse the piece into
liquid nitrogen several times to maintain its solid
consistency. When a sufficient amount of tissue
was prepared, a 22-gauge needle (Ultradent Products)
was used to aspirate part of it and then the needle was
inserted in its place in the model until it reached the
outer end of the simulated accessory canal. The tissue
was injected in the accessory canal until part of it
(a) (b)
(c) (d)
Figure 1 Preparation of an epoxy resin
model used in this study: (a) template
to ensure similar simulated accessory
canal position and angulation between
the models; (b) positioning of the finger
spreader and the wires; (c) mould
made of pink wax filled with epoxy resin;
(d) finished model.
Al-Jadaa et al. PUI in accessory canals
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 59–65, 2009 61
extruded into the main canal. Excess tissue was placed
in the wide entrance of the carrying needle to obtain
a passive closure simulating a pathosis rather than
a tight seal of the simulated accessory canals. This
procedure was repeated in all the five simulated
accessory canals in each model.
The models were re-filled for the control experiments
with heated NaOCl and NaOCl at room temperature
(see below) after removing the old tissue from accessory
canals and extensive rinsing with tap water.
Control experiments on temperature
It is well known that ultrasonic irrigant activation is
associated with heat generation (Cunningham et al.
1982, Cameron 1988). An increase in temperature can
enhance the efficacy of NaOCl (Sirtes et al. 2005). To
discern between pure temperature and other ultrasonic
effects on NaOCl, the temperature associated with PUI
in the current model was determined. A preliminary
study was carried out using one of the models
fabricated for the study. The temperature was recorded
after each 1 min of activation and also after each flush
with 1 mL 2.5% (wt/vol) NaOCl using a thin couple
wire connected to a calibrated temperature measuring
device (Testo Term 9010, Lenzkirch, Germany). This
procedure was carried out over 5 min and repeated
thrice. After the intracanal temperature created by PUI
in the current set-up was known, the irrigant temper-
ature to be used in the second part of the study was
determined by trial. The irrigant was heated by placing
the irrigation syringe inside a water bath and the
temperature was measured after each irrigation by
1 mL of 2.5% NaOCl and after 1 min of irrigation. After
that 1 min the syringe was returned to the water bath
to ensure a stable temperature. The irrigant tempera-
ture inside the syringe was measured by introducing
the couple wire through its opening just before
irrigation. The temperature was raised gradually until
the suitable temperature inside the canal was achieved.
This procedure was repeated thrice.
Main experiment
The model was held on a cone especially designed to
direct light through it to have a contrast facilitating the
interpretation of results and to prevent artefacts caused
by over-exposure of light. Halogen light (Intralux
4000-1, Volpi AG, Schlieren, Switzerland) was intro-
duced from behind the model and through the cone. An
initial photograph using a 10-megapixel camera
(Nikon D200, Tokyo, Japan) mounted on a stand in
front of the model was taken to ensure the complete
filling of the simulated accessory canals with pulp tissue
and to allow comparison later on. The irrigation
protocol was as follows: 1 mL of 2.5% NaOCl at room
temperature was introduced to full canal length by a
long irrigation needle with 30-gauge diameter (Max-i-
Probe, Hawe Neos, Bioggio, Switzerland). Care was
exercised that the opening at the needle tip was not
directed towards the accessory canals directly. An
ultrasonic device (EMS 400, EMS, Nyon, Switzerland)
with its power set at the ¼ of the scale, with an
ultrasonic stainless steel K-type file size 15 (Endoso-
nore, Dentsply Maillefer) mounted on an ultrasonic
adaptor (Piezon, 90� Endo File Holder, EMS) was used
to activate the irrigant in the canal with an up and
down motion by hand at a ratio of 10 mm s)1 to the
full length of the canal minus half a millimeter, for
1 min. Subsequently, a photo was taken and the main
canal was irrigated with 1 mL of sodium hypochlorite
at room temperature. The same procedure was
repeated every minute for 5 min. At the end of the
fifth minute, the temperature inside the canal was
measured to ensure that the ultrasonic file was active.
The ultrasonic file was replaced for each model to avoid
fracture, whilst the ultrasonic adaptor was replaced
after two models. This protocol was carried out on the
seven models. In the control experiments, the models
were refilled with tissues as described before and the
same procedure was carried out except for the NaOCl
temperature which was 68–69 �C in the second
experiment and at room temperature the third time.
The file was introduced in the canal without ultrasonic
activation in these two experiments. The experiment
for the second and third parts was carried out only on
six models because one of the models was lost because
of a fractured file in the first part. Results from that
model were discarded.
Data generation and analysis
Data from the temperature experiments are presented
as means and standard deviations (n = 3).
The photos were analyzed using the ImageJ program
(nih.gov; National Institute of Health, Bethesda, MD,
USA). The outcome variable assessed here was distance
of tissue dissolution in simulated accessory canal,
measured from the canal entrance to the closest
tissue-irrigant interface. Measurements were performed
by one operator, who was tested for his accuracy by
analysing the same images ten times after different
PUI in accessory canals Al-Jadaa et al.
International Endodontic Journal, 42, 59–65, 2009 ª 2009 International Endodontic Journal62
intervals. The error of the individual measurement was
< 0.05 mm. Consequently, data pertaining to tissue
dissolution were rounded to 0.1 mm. To compare
overall tissue dissolution at room temperature with the
corresponding values obtained by PUI and in the
temperature-controlled experiments, the sums of dis-
tances of tissue dissolution in all accessory canals per
model were averaged for each mode (n = 6) and
compared by a paired t-test. To compare the impact of
accessory canal position and angulation on tissue
dissolution by PUI, mean values per simulated accessory
canal were compared by one-way analysis of variance
(anova). Bonferroni’s correction was applied for multi-
ple testing. The alpha-type error was set at 0.05.
Results
Temperature
Passive ultrasonic irrigation caused a rise in hypochlo-
rite temperature in the main canal to 53.5 ± 2.7 �Cafter the fifth min (Fig. 2). For the temperature-control
experiment, the suitable irrigant temperature in the
syringe was found to be 68–69 �C, which was achieved
by placing the 5-mL irrigation syringe in a water bath
of 75 �C for 5 min. This resulted in an overall
temperature in the canal that was similar to the one
observed with PUI (Fig. 2).
One of the observations, which might affect the
clinical usability of PUI, was that after multiple usage of
the ultrasonic adaptor (usually after 12–14 min of
activation), the temperature suddenly dropped, indicat-
ing a loss of ultrasonic energy transmitted to the irrigant
in the canal. After multiple trials and by exclusion it was
found that the rubber ring between the two parts of the
ultrasonic adaptor wore out so that there was less
activation of the ultrasonic file. This observation
necessitated a regular replacement of the adaptor. As
an extra precaution the temperature wasmeasured after
the fifth and final minute of PUI in each individual model
as an indicator of the ultrasonic activity inside the canal.
Tissue dissolution
The mean sums of dissolved tissue from simulated
accessory canals after 5 min of PUI or the mock
treatments were: PUI: 6.4 ± 2.1 mm, mock treatment
at room temperature: 0.8 ± 0.3 mm, and mock treat-
ment controlled for heat: 1.4 ± 0.6 mm. The difference
between the heated irrigant and the counterpart
administered at room temperature was not significant
at the 0.05 level, whilst there was a significant
(P < 0.05) difference between both these treatments
and PUI, indicating a clear PUI effect.
When the influence of simulated accessory canal
position and angulation on tissue dissolution by PUI
was studied (Table 1), it was noted that regardless of
accessory canal position or angulation, a plateau was
reached after the third minute of activation. Further-
more, there was no significant difference in tissue
dissolution between different simulated accessory
canals at any time.
Discussion
The current study showed a positive effect of PUI in
conjunction with a sodium hypochlorite irrigant on
pulp tissue dissolution from simulated accessory canals
in an epoxy resin model. This effect was not explained
by a simple rise in overall irrigant temperature.
The current study is limited by the fact that epoxy
resin is a completely different material from human
dentine, and direct clinical conclusions can therefore
not be drawn from the results presented here. Further-
Figure 2 Temperatures (�C) measured in
the simulated main canal after passive
ultrasonic irrigation (blue) and during
the mock treatment with a heated
sodium hypochlorite solution (red) over
time. Dots indicate means, error bars
standard deviations (n = 3).
Al-Jadaa et al. PUI in accessory canals
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 59–65, 2009 63
more, the simulated main canal in the current model
was straight. This type of anatomy is rarely encountered
in natural teeth. However, the aim of this study was to
discern between mere temperature and other PUI effects
in the cleansing of accessory canals. For this purpose,
the model appeared adequate. However, despite the
standardization of the models that were used, data
variation pertaining to the distance of dissolved tissue in
simulated accessory canals was still relatively large as
indicated by the high standard deviations (Table 1).
This can be explained by the difficulty in obtaining
completely homogenous and standardized fills of
necrotic tissue in these thin canals. On the other hand,
the density of necrotic tissue in infected natural
accessory canals might also vary. It is a common
observation when dealing with natural tissues such as
the bovine pulps that were used in the current inves-
tigation that outcomes vary. In addition, because the
ultrasonic tip was guided by hand, it was impossible to
control where it touched the canal wall, which may also
have contributed to the variance in outcome. A further
limitation of this study is the fact that the average width
of accessory canals is not known or published (De Deus
1975). However, based on our own observations on
micro-computer tomographies of human teeth, 200 lmappeared to be a fair approximation.
The temperature that was measured in the current
study was somewhat higher than that measured in
natural teeth, which may be because of the fact that
thermal transducing properties of dentine differ from
those of epoxy resin (Brown et al. 1970) and also
because of the potential cooling effect of the blood
circulation around natural teeth. Using PUI with
intermittent flushes, temperatures of up to 45 �C were
measured in root canals of natural teeth after 30 s of
ultrasonic irrigant activation (Cameron 1988). Consid-
ering the shorter activation times, there appears to be
little variance between these published data and the
current results. However, other researchers found the
temperature rise in the root canal promoted by PUI to
be minimal (Ahmad 1990). However, a root canals
were widened to an ISO-size 80 in that study, and there
was continuous flow of irrigant during ultrasonic
activation which might explain the differences.
The exact mechanism by which ultrasonic hypo-
chlorite activation can affect the tissue in accessory
canals is still unclear. One hypothetical mechanism is
the collapse of bubbles during transient cavitation that
produces a pressure-vacuum effect, which sucks the
canal content to the inside rather than pushing it
further in the canal. This will be followed by diffusion of
the irrigant in the main canal to substitute the space
created (Martin & Cunningham 1985). Another possi-
bility is that the streaming around the activated file
because of the cohesion between fluid particles inside
the accessory canal and the irrigant in the main canal
sucks the content of the accessory canals into the main
canal with fluid flow toward the main canal (Ahmad
et al. 1992). The third possibility is a local temperature
effect because of the collapse of bubbles during transi-
tional cavitation. It has been shown that locally, the
temperature can reach up to 5000 �C with heating and
cooling rates greater than 109 K/s during cavitation
(Suslick 1990). Consequently, a great part of the
ultrasonic effect may still be thermal, but just not
measurable by assessing the overall irrigant tempera-
ture. However, it is still unclear at this point whether
transient cavitation occurs in the root canal. Based on
preliminary observations with dye solutions of different
colours in the model described here, it was noted that
little streaming occurred in the apical area, especially in
the simulated accessory canal at 180� at the apical endof the main canal (not shown). Nevertheless, tissue
dissolution was similar regardless of accessory canal
position or angulation in the current study. Conse-
quently, it may be so that cavitation was, at least in
part, responsible for the observed phenomenon of tissue
dissolution by PUI. This again highlights what has been
pointed out more than 20 years ago, namely that
further studies are required to elucidate the phenomena
behind ultrasonic effects that might or might not occur
in the root canal.
Table 1 Distance in mm of dissolved tissue as measured from the simulated accessory canal entrance after passive ultrasonic
irrigation (means and standard deviations, n = 6)
Time 90�, mid-canal 45�, mid-canal 90�, apex 45�, apex 180�, apex
1st min 0.2 ± 0.3 0.1 ± 0.2 0.0 ± 0.0 0.4 ± 0.6 0.1 ± 0.1
2nd min 1.1 ± 0.5 0.8 ± 0.6a 0.9 ± 0.3 1.3 ± 0.8 0.5 ± 0.6
3rd min 1.4 ± 0.5 1.0 ± 0.6 1.1 ± 0.3 1.5 ± 0.9 0.7 ± 0.7
4th min 1.4 ± 0.5 1.1 ± 0.6 1.2 ± 0.3 1.6 ± 0.8 0.8 ± 0.8
5th min 1.5 ± 0.6 1.2 ± 0.6 1.3 ± 0.3 1.7 ± 0.8 0.9 ± 0.9
No statistically significant differences were found between canals at any given time (P > 0.05, anova, Bonferroni).
PUI in accessory canals Al-Jadaa et al.
International Endodontic Journal, 42, 59–65, 2009 ª 2009 International Endodontic Journal64
One further observation that was made during the
current study was that because of the high corrosive
potential of hypochlorite and the heat that is generated
during ultrasonic activation, material wear out oc-
curred rapidly. Initially, noncutting nickel-titanium tips
were used, but these fractured so frequently that it was
decided to use the cheaper stainless-steel files. Results
between the two types of instruments were similar
(data not shown).
Conclusions
• A model allowing the quantitative assessment of
necrotic pulp tissue dissolution in simulated accessory
canals was presented.
• The temperature generated in the main canal of this
model by passive ultrasonic activation of a 2.5% NaOCl
solution was over 50 �C.• This rise in overall temperature could not be
responsible for the effectiveness of PUI.
• Tissue dissolution by PUI was irrespective of simu-
lated accessory canal position or angulation.
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Al-Jadaa et al. PUI in accessory canals
ª 2009 International Endodontic Journal International Endodontic Journal, 42, 59–65, 2009 65
CLINICAL ARTICLE
A preliminary study of the use ofperipheral quantitative computedtomography for investigating root canalanatomy
M. T. Sberna1, G. Rizzo2, E. Zacchi3, P. Cappare1 & A. Rubinacci3
1Department of Odontoiatrics; 2IBFM-CNR, Department of Nuclear Medicine; and 3Bone
Metabolic Unit, Scientific Institute H San Raffaele, Milan, Italy
Abstract
Sberna MT, Rizzo G, Zacchi E, Cappare P, Rubinacci A. A preliminary study of the use of
peripheral quantitative computed tomography for investigating root canal anatomy. International Endo-
dontic Journal, 42, 66–75, 2009.
Aim To evaluate the use of peripheral quantitative computed tomography (pQCT) for
qualitative and quantitative analysis of root canal anatomy and for assessing the extent of
canal enlargement during root canal instrumentation.
Summary The volumevariation achievedbyS1ProTaper instruments in the coronal third of
the root canals was analysed using peripheral computed tomography. The tooth was
scanned in the horizontal plane producing 36 consecutive cross-sectional images. All images
were the result of 360 projections with a section thickness of 250 lm, a distance between
slices of 0.5 mm and an in-plane pixel size of 70 · 70 lm. The evaluation was completed
before and after S1 ProTaper instrumentation (with or without circumferential filing) of one
root canal of a freshly extracted maxillary first premolar tooth. The acquired images were
realigned geometrically and processed using a 3D visualization software. pQCT scanning
allowed 3D reconstruction of the root canal anatomy and the assessment of the extent of
canal enlargement during root canal instrumentationwith lateral displacement of canal walls
and hence volume change being greater than the coefficient of variation. The densitometry
evaluation showed uniform density along the root canal wall.
Key learning points
• pQCT scanning allowed 3D reconstruction of the root canal anatomy and the
assessment of the extent of canal enlargement during root canal instrumentation.
• pQCT shows promise for allowing qualitative and quantitative analysis of endodontic
procedures.
Keywords: 3D imaging, peripheral quantitative computed tomography, qualitative and
quantitative methodology, root canal instrumentation, root canal preparation.
Received 17 July 2007; accepted 2 June 2008
Correspondence: Alessandro Rubinacci, Bone Metabolic Unit, Scientific Institute H San
Raffaele, via Olgettina, 60, 20132 Milan, Italy (Tel.: +39 0226432320; fax: +39 0226433038;
e-mail: [email protected]).
International Endodontic Journal, 42, 66–75, 2009 ª 2008 International Endodontic Journal
doi:10.1111/j.1365-2591.2008.01452.x
66
Introduction
Precise morphological mapping of the root canal system is a prerequisite for the
evaluation of endodontic instruments and procedures. A detailed understanding of the
root canal system is, in fact, critical for the characterization of all factors that might have a
significant impact on the volume of root canals and pulp chambers and in the development
of successful therapeutic strategies. Conventional destructive approaches based upon 3D
computer-based reconstructions of histological sections do not allow a longitudinal
assessment of the endodontic therapy, are limited by the poor precision of the volumetric
algorithms, and do not permit a systematic mapping of the endodontic volumes (Walton
1976). Several non-destructive approaches have been developed more recently. For
example, computed tomography has been applied extensively to the detection of enamel
thickness from an anthropological perspective (Gantt et al. 2006), but the available
resolution did not allow a precise mapping of the root canal nor the estimation of the canal
volumes that were usually overestimated (Gantt et al. 2006). The inability of conventional
imaging techniques to visualize the root canal system drove the development of
alternative imaging modalities. In this context, two procedures have proven to be suitable
for the non-destructive exploration of both teeth and the volumetry of the root canals,
namely magnetic resonance microscopy (MRM) and X-ray computed microtomography
(lCT).
Magnetic resonance microscopy, a high-resolution magnetic resonance spectroscopy
system, constitutes a powerful tool for a detailed analysis of teeth without applying
ionizing radiation (Tseng et al. 2007). However, standard methodologies require a strong
proton signal of the surrounding liquid to produce a boundary surface image to visualize
the mineralized tissue. Magnetic resonance tomography (MRT) with stray field imaging
(STRAFI) (Baumann et al. 1993) can achieve this directly, in a very short T2 time, but with
poor resolution and the different hard tooth tissue components cannot be differentiated as
in the case of MRM. Imaging of all structural components of a tooth with one system and
one image was not possible until the demonstration that constant-time imaging (CTI)
techniques enabled the detection of magnetic signals from the hard tooth tissues, as well
as from the proton- and signal-intensive pulpal tissue. By presenting both signals in one
image with a resolution as low as 195 lm, CTI combines the advantages of both the
standard MRM and the STRAFI (Appel & Baumann 2002), but it might be limited in the
qualitative and quantitative description of the smallest components of the pulpal chamber.
The lCT is a miniaturized form of conventional computerized tomography. The lCT
scanner uses an X-ray tube as radiation source and a 3D reconstruction algorithm.
Recently, lCT has been introduced to evaluate not only cross-sections of roots but also 3D
shapes of canal systems at resolutions as high as 36 lm (Dowker et al. 1997, Bjørndal
et al. 1999, Rhodes et al.1999, Peters et al. 2000, 2001, Bergmans et al. 2001, Gluskin
et al. 2001, Gao et al. 2006, Lee et al. 2006). This innovation was achieved because new
hardware and software were available to evaluate the metrical data created by lCT, thus
allowing geometrical changes in prepared canals to be determined more precisely. This
technique has two disadvantages: it is limited to the processing of two extracted teeth at
a time because of the small size of the gantry and has a long scanning time up to 6 h
(Peters et al. 2003). New developments include high-resolution X-ray computed tomog-
raphy (HRXCT) and flat panel-based volume computed tomography (fpVCT). HRXCT is
applied to the 3D reconstruction of enamel thickness, and of dentine and pulp chamber
volumes at a resolution ranging from 5 to 100 lm by exporting two-dimensional digitized
images obtained by combining modular energy sources (125–450 kV) and modular
detectors (Gantt et al. 2006). The fpVCT has also been found suitable for the qualitative
visualization of the root canal system despite its low spatial resolution of 150 lm. This
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ª 2008 International Endodontic Journal International Endodontic Journal, 42, 66–75, 2009 67
technique is in fact able to visualize dentine, enamel and the root canal system in 3D-
image reconstruction that, because of the size of the gantry (40 cm in diameter), might
include several teeth at the same scanning time (Hannig et al. 2006).
However, a systematic evaluation of endodontic instruments and procedures based
upon these instruments is not practicable, given their high cost and limited availability.
Therefore, the following study is designed to evaluate the feasibility of applying peripheral
quantitative computed tomography (pQCT) to the qualitative and quantitative analysis of
root canal anatomy and for assessing the extent of canal enlargement during root canal
instrumentation. pQCT has been originally designed for the diagnosis of osteoporosis in
humans, rats and mice (Schmidt et al. 2003). The unit works with a specially developed
X-ray tube having a minute focal spot whilst the detector system consists of a series of
miniature semiconductor crystals. The device is equipped with a special detector
collimator that can be switched up to four collimator sizes corresponding to the four
section thicknesses (100, 250, 500 and 750 lm). Although the planar resolution of pQCT
(70 · 70 lm) does not have the same resolution as lCT, it might provide a nondestructive
morphological investigation at low cost and shorter scanning times.
Materials and methods
Specimen selection and preparation
The study is preliminary in nature, with only one tooth analysed. One root canal of a
maxillary first premolar tooth, freshly extracted for clinical reasons and not relating to this
study, was selected. After preparing a standard access cavity, the canal was passively
negotiated with sizes 10 and 20 K-files to the apical foramen; the working length was
determined visually.
Canal preparation was completed by a single operator using Ni–Ti rotary instrumenta-
tion; the S1 ProTaper (Dentsply Maillefer, Ballaigues, Switzerland) was mounted on an
ATR Tecnika Vision system (motor and handpiece) (ATR, Pistoia, Italy).
For assessing the extent of canal enlargement during root canal instrumentation, two
different applications of S1 ProTaper on the coronal third of the root canal were
considered: the first in compliance with the manufacturer’s protocol and the other
arbitrarily modified to produce a loss of the canal wall structure. Therefore, S1 ProTaper
was used, for approximately 9 s, until reaching 1 mm from the working length, centering
and avoiding any lateral movement (first phase), then applying lateral displacement
(second phase) for a further 9 s. The instrumentation was deliberately applied to one side
of the root canal system, leaving the other side untreated as a control.
Scanning
Tomographic tooth scanning and measurements were obtained before and after each
instrumentation phase.
A pQCT scanner was used for the measurements (Research SA+; Stratec Medizin-
technik GmbH, Pforzheim, Germany). This translation rotation scanner works with a
specially developed X-ray tube with a 50-lm spot size (high voltage 50 kV, anode current
<0.3 mA, mean X-ray energy 37 keV, energy distribution after filtration 18 keV full width
half maximum [FWHM]). The detector-system consists of 12 miniature semiconductor
crystals with amplifiers. The precision error supplied by the manufacture for density
measurement in vivo is around 1.5%.
The tooth was scanned in the horizontal plane producing 36 consecutive cross-sectional
images at a distance of 0.5 mm.
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International Endodontic Journal, 42, 66–75, 2009 ª 2008 International Endodontic Journal68
All images were obtained with 360 projections, with a section thickness of 250 lm and
at an in-plane pixel size of 70 · 70 lm at a scan speed of 3 mm s)1. Total scanning time
was 4 h. Operator time was limited to 10 min.
Scanning of a selected region of the root canal was also obtainedwith a section thickness
of 100 lm.As no additional informationwas available, this scanning procedurewas aborted.
To orientate the long axes of the tooth parallel to the image planes, the tooth was fixed
with manufacturer-made plastic holders. The correct longitudinal positioning was
determined by means of an initial scout scan.
Qualitative data analysis
To correct the possible mispositioning of the specimen in the pQCT gantry, the acquired
studies were geometrically realigned using a registration technique based on the
maximization of mutual information implemented in a home-made software package
(Rizzo et al. 2005). After registration, the studies corresponded geometrically, with sub-
voxel accuracy, and could be compared correctly.
The registered images were then processed using 3D visualization software (amira 4.1;
Mercury Computer System Inc., Chelmsford, MA, USA) to generate 3D rendering of the
tooth external surface and the root canal, for the qualitative evaluation of the modification
of the root canal size, produced by the S1 ProTaper. The coefficient of variation of the
reconstructed volumes after repositioning was assessed by performing the quantitative
analysis on the actual cross-sections of the root canal that had not undergone to
instrumentation. It varied from 3.3% to 7.1%.
Quantitative data analysis
A quantitative assessment of the canal volume variations induced by the instrumentation
was carried out using the 3D analysis software ‘analyze’ (Biodynamic Research Unit,
Mayo Clinic, Rochester, MN, USA) (Robb et al. 1989). From each registered image, the
root canal volume, corresponding to the area of interaction of S1 ProTaper (coronal third of
the root canal), was extracted, by calculating, on each slice, the isocontour corresponding
to the same isovalue. The volume of the dentine removed was then obtained by
subtracting the canal volumes after and before treatments.
Furthermore, a densitometry evaluation was performed, with the pQCT scanner, which
directly provided sectional images accurately calibrated in terms of density. Dentine
density in each scan was calculated by analyze. For this purpose, densities <500 mg cm)3
corresponding to the tooth canal or >2000 mg cm)3 corresponding to the tooth enamel
were excluded.
Results
Qualitative evaluation
In Fig. 1, the 3D representation of the external tooth surface and the root canal is shown
for each study, after spatial registration. From the qualitative analysis it is possible to note
the effect of using ProTaper in a lateral displacement mode: the size of the treated canal
area is enlarged (see arrow).
The same effect can be seen in Fig. 2, which visualizes the surface of the canals, before
and after the treatments. The increment of canal volume is evidentwhenProTaper is used in
a lateral displacement mode (Fig. 2e) but is not noticeable when ProTaper is used more
passively (Fig. 2d).
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ª 2008 International Endodontic Journal International Endodontic Journal, 42, 66–75, 2009 69
Figure 1 Representative 3D rendering of the external tooth surface and canal for each experimental
condition. Left: treatment with K-file 20 instrumentation. Middle: treatment with S.1 ProTaper
instrumentation used as protocol. Right: treatment with S.1 ProTaper instrumentation used by lateral
displacement. The enlargement of treated area (arrow) is clearly visible in the third situation.
(a) (b)
(d) (e)
(c)
Figure 2 Comparison of 3D rendering of the canal surfaces in different conditions. Top row: (a) K-file
20 (white), (b) S1 ProTaper as protocol (green), (c) S1 ProTaper with lateral displacement (red). Bottom
row: (d) superposition of S1 ProTaper as protocol and K-file 20, (e) superposition of S1 ProTaper as
lateral displacement and K-file 20. In this last figure, the enlargement of canal using S1 ProTaper as
lateral displacement results in an evident red area on the reference K-file 20 white surface.
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Quantitative evaluation
Figure 3 shows orthogonal views corresponding to the 3D conditions after registration,
with the region of interest (treated area) superimposed as red overlay.
The measured volume sizes for each slice belonging to the treated area are shown in
Fig. 4. Lateral displacement produced volume changes far above those detected when
ProTaper is used more passively. By applying lateral displacement between the K-file and
S1 used in a brushing mode, volume changes ranged from +0.09 mm3 (38 voxels) in slice
Figure 3 Tooth cross-sectional views corresponding to the three different experimental conditions.
Top row: treatment with K-file 20. Middle row: treatment with S1 ProTaper used as protocol. Bottom
row: treatment with S1 ProTaper used as lateral displacement. The red overlay corresponds to the
treated area.
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23 to +0.18 mm3 (72 voxels) in slice 26, whereas without lateral displacement volume
changes ranged from )0.030 mm3 (or 12 voxels) in slice 23 to +0.049 mm3 (or 20 voxels)
in slice 26.
The measured volume sizes for the reconstructed treated area were 2.56 mm3 before
S1 ProTaper, 2.63 mm3 after S1 ProTaper without lateral displacement, and 3.10 mm3
after S1 ProTaper with lateral displacement. This resulted in an increment of 2.66% of the
canal volume when ProTaper was used more passively, and in an increment of 21% when
lateral displacement was applied. Whilst the former increment was in the range of the
coefficient of variation, as assessed on the root canal not undergoing to instrumentation
(3.3–7.1%), the latter was far above. As not more than one tooth was used, no significant
statistical calculation can be presented.
The cross sectional densitometric analysis was able to identify the dentinoenamel
junction that was represented in Fig. 5. The density distribution pathway clearly
distinguished dentine density from enamel. The longitudinal densitometric analysis
globally shows no differences in the density of dentine: as illustrated in Fig. 6, the profile is
flat and only small density gradients can be observed for the first curve points, principally
because of partial volume effects induced by slice thickness.
Figure 4 Comparison of tooth canal volumes in the three different experimental conditions. Volumes
were measured in all the slices belonging to the treated area (slice 23–26, total longitudinal extension:
2000 lm).
Figure 5 Typical cross-sectional density profile showing the density of the enamel and dentine. The
abrupt drop in the density profile corresponds to the dentinoenamel junction.
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Discussion
The study has shown that pQCT instruments, developed for bone mineral analysis and
having a spatial resolution of 70 · 70 · 250 lm, show promise for allowing a precise and
reliable mapping of the root canal system by producing contiguous slices of teeth. The 3D-
image reconstruction and the measurements of volumes and densities obtained by pQCT
scanning appear to be suitable for the qualitative and quantitative assessment of the
changes in root canal shape following instrumentation. The application of a pQCT system to
endodontic imaging offers advantages over current NMR and lCT techniques, mainly
relating to its lower cost and wider availability, whilst scanning time is only marginally
reduced (4 h vs. 6 h). pQCT allows direct visualization of tooth tissues, i.e. dentine, enamel
and root canal system,which are clearly distinguishable in the 3D images, and candetermine
the impact of spatial distribution of the dental volumetric density (enamel versus dentine) on
dental pathology. This has not been systematically evaluated and offers potential
advantages on our current understanding of the genetic and environmentally related
differences in dentine signalling that could alter enamel structure with an impact on dental
health. A minor advantage of pQCT is related to its large scanner gantry opening (9 cm) that
can include several teeth at the same scanning time as fpVCT (Hannig et al. 2006), whereas
lCT systems can allowevaluation of two teeth only (Peters et al. 2001). The acquired data at
each repositioning were realigned geometrically before comparison using a registration
technique based on the maximization of mutual information implemented in a home-made
software package (Rizzo et al. 2005). As the registered sections were geometrically aligned
with sub-voxel accuracy, the comparisons should be considered precise and reliable. The
detection of volume changes at the side of the root canal system, only where they were
expected to be found after adequate instrumentation, sustains a potential application of the
developed methodology in the clinical setting. When pQCT, lCT and histomorphometry
were compared, the results showed that a pQCT scanning at 500-lm thickness can yield
satisfactory precision and accuracy in microstructural representation of the scanned bone
site (Schmidt et al. 2003). The highest agreement was found between pQCT and lCT being
based on the measurement of the same physical property as X-ray absorption.
However, a rigorous analysis of the limits of the pQCT in reconstructing small canals
should be outlined. The larger pixel size (70 · 70 lm), and the consequent lower
resolution of the pQCT versus lCT, introduces larger partial volume effects that might
Figure 6 Dentine density measured in the scan correspond to K-file 20 treatment. Slices 1 and 36 are
not considered, as they contain very few voxels of dentine.
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affect the volumetric evaluation of the pulp chamber and root canals as well as the
definition of the dentinoenamel junction and the derived parameters as density. Even if
the object of theoretical correction (Rittweger et al. 2004), this limitation is critical and is
applied when projecting a continuous object on a discrete grid. Hence, quantitative
image analysis is prone to errors where the edge of the object is within the sampling
grid. The segmentation process can overestimate sharp edges depending upon the voxel
volumes as the partial volume effect increases with voxel size (i.e. at lower image
resolution) and decreases with the object size. This implies that side and/or accessory
canals as well as main canals smaller than the voxel size are not detectable with
sufficient accuracy, thus hampering correct visualization and analysis. The spatial
resolution of the pQCT methodology applied is critical to the reliability of volume change
measurements. It is generally accepted that half voxel size for each voxel forming the
volume surface contributes to the uncertainty range in volume estimate, because of
spatial resolution. It follows that, in the case of the root canal system, the uncertainty
varies along the canal and is related to its size. By approximating to a cylinder the shape
of the root canal represented in a single tomographic slice, the measurement uncertainty
of the volume changes observed should be expected ranging from 10% to 11% (from 28
to 31 voxels) for canal volume ranging from 250 to 298 voxels (slices 23–26). This
quantitative analysis suggests that the volume changes observed when lateral displace-
ment was applied were reliable and, as a consequence, lateral displacement should be
avoided to preserve optimal mechanical strength of tooth. In fact, the potential for the
root filled teeth to fracture increases proportionally with the amount of dentine removed
(Pilo et al. 1998).
Conclusion
This study has presented an innovative and nondestructive methodology to illustrate canal
morphology and canal volume changes after instrumentation by applying pQCT analysis.
The 3D reconstruction methodology based on pQCT images described here deserves
further systematic evaluation to fully validate its application in the clinical setting as a tool
for qualitative and quantitative analysis of the endodontic procedures.
Disclaimer
Whilst this article has been subjected to Editorial review, the opinions expressed, unless
specifically indicated, are those of the author. The views expressed do not necessarily
represent best practice, or the views of the IEJ Editorial Board, or of its affiliated Specialist
Societies.
Acknowledgements
Wewish to acknowledge Johannes Willnecker, Stratec Medizintechnik GmbH, Pforzheim,
Germany, for providing the technical information required for the development of the study.
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CASE REPORT
Endodontic management of badlybroken down teeth using the canalprojection system: two case reports
A. S. Bhomavat, R. K. Manjunatha, R. N. Rao & K. H. KidiyoorDepartment of Conservative Dentistry and Endodontics, S.D.M. College of Dental Sciences and
Hospital, Dharwad, Karnataka, India
Abstract
Bhomavat AS, Manjunatha RK, Rao RN, Kidiyoor KH. Endodontic management of
badly broken down teeth using the canal projection system: two case reports. International Endodontic
Journal, 42, 76–83, 2009.
Aim Teeth that have been weakened by caries and require root canal treatment to
maintain their functional integrity may present with minimal coronal tooth structure and
are a challenge for isolation and restoration. The aim of this clinical report is to
demonstrate the management of badly broken down teeth using the Projector Endodontic
Instrument Guidance System (PEIGS).
Summary The PEIGS is an adjunct to root canal treatment designed to enhance the ease
of treatment delivery. Use of this system facilitates projection of canal orifices from the
floor of the pulp chamber to the cavosurface, providing direct visualization of and physical
access to the projected canals. This report demonstrates the use of this novel device for
the management of two badly broken down teeth.
Key learning points
Use of the endodontic projection system has the following advantages:
• ‘Projects’ the canal orifice from the floor of the pulp chamber to the cavosurface,
thereby enhancing visualization and access to the canals.
• The bonded coronal build up reduces the risk of interappointment crack initiation and
coronal-radicular fracture of weakened tooth structure.
• Permits individualization of canals especially when they lie in close proximity to each
other on the chamber floor.
• Isolation may be facilitated by ease of clamp retention, rendering many structurally
debilitated teeth endodontically treatable.
Keywords: broken down teeth, endodontic canal projection, isolation, pre-endodontic
build-up, projector.
Received 15 September 2007; accepted 13 July 2008
doi:10.1111/j.1365-2591.2008.01465.x
Correspondence: Dr Anisha S. Bhomavat, Department of Conservative Dentistry and
Endodontics, S.D.M. College of Dental Sciences and Hospital, Sattur, Dharwad – 580009,
Karnataka, India (Tel.: +91 9314130001, +91 22 28330846; fax: +91 836 2467612;
e-mail: [email protected]).
International Endodontic Journal, 42, 76–83, 2009 ª 2008 International Endodontic Journal76
Introduction
Technical and scientific advances in endodontics have resulted in retention of teeth, which
were earlier deemed untreatable (Johns et al. 2006). It is universally accepted that
preservation of a natural tooth with a good prognosis is superior to tooth loss and
replacement (Roda & Gettleman 2006).
The current techniques employed tomanage severely broken down teeth include the use
of special clamps with specific designs, surgical exposure of the cervical tooth structure to
facilitate clamp placement, use of orthodontic bands, preformed copper bands, pin or
adhesive retained amalgam, composite and glass ionomer buildups. However, these have
inherent disadvantages (Madisonet al.1986, Jeffrey&Woolford1989). Presenceofminimal
coronal structure can risk further damage to the crown during rubber dam clamp placement
thereby compromising isolation and causing subsequent coronal leakage (Jeffrey &
Woolford 1989, Zerr et al. 1996). Pre-endodontic build-up of the coronal tooth structure
following caries removal and identification of the canal orifices can facilitate the endodontic
process by providing a strong core and coronal seal (Kurtzman 2004).
The canal projection technique using the Projector Endodontic Instrument Guidance
System (PEIGS) (CJM Engineering, Santa Barbara, CA, USA) provides pre-endodontic
reconstruction of debilitated coronal and radicular tooth structure whilst preserving
individualized access to canals (Kurtzman 2004, http://www.cjmengineering.com). This
case report introduces the innovative concept of using the ‘Projector’ which ‘projects’ the
canal orifices from the chamber floor to the cavosurface providing better visibility and
access (Weathers 2004), and also ensures optimum isolation and reinforcement of the
tooth structure.
Case reports
Case report 1
A 36-year-old female reported to the Department of Conservative Dentistry and
Endodontics, S.D.M. College of Dental Sciences, Dharwad, India, complaining of a dull,
mild intermittent pain in the right maxillary posterior region for 2 months. Intra-oral
examination revealed the presence of a grossly decayed tooth, 16 (FDI), with three walls
missing (Fig. 1a). Pulp sensibility testing elicited a negative response. The preoperative
radiograph (Fig. 1b) revealed deep occlusal caries involving the pulp and widening of the
periodontal ligament space in relation to the palatal root. A diagnosis of pulpal necrosis and
chronic periradicular periodontitis was made.
Root canal treatment was then planned using the PEIGS as rubber dam isolation was
challenging. The Projector is a small, black, cone-shaped plastic device, which slides onto
an endodontic file (Fig. 1d). It has a central lumen, an apical bevel and is made of a
specially formulated plastic (linear low-density polyethylene) which is nonadherent to
dental restorative materials. It is available in two sizes; ‘regular’ which is used in cases
where the size of the access cavity is adequate to accommodate the medium-sized
device, and ‘skinny’ which is used in cases where the size of the access cavity is not
adequate to accommodate the medium-sized device (Table 1).
After securing adequate anaesthesia and application of rubber dam with a clamp with
apically inclined beaks, caries was excavated. Access cavity preparation was performed
and four canal orifices were identified (Fig. 1c). The canals were enlarged to a size 20 file
using the standardized method of cleaning and shaping. Canal orifices were dimpled with
a slow speed round bur (Mani Inc., Tochigi-Ken, Japan) of diameter 1 mm, to facilitate
placement of the projectors and to prevent flow of adhesive into the canals.
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ª 2008 International Endodontic Journal International Endodontic Journal, 42, 76–83, 2009 77
A stainless steel automatrix band (Hawe Supermat�; KerrHawe, Lugano, Switzerland)
was placed followed by the application of phosphoric acid gel (Scotchbond Etchant gel;
3M ESPE, St Paul, MN, USA) to etch the exposed dentine and enamel. Rinsing and drying
was accomplished after 30 s. The Projectors were placed on four endodontic files and slid
up toward the file handles, so that 5–8 mm of each file tip protruded beyond the tip of the
Projector. Different sizes of files were used to aid in identification of the projected orifices.
Size 20 was used for the mesiobuccal canal, size 15 for the second mesiobuccal canal,
size 25 for the distobuccal canal and size 30 for the palatal canal. Each file with a Projector
was then inserted into its respective orifice and the Projector was pressed into place with
cotton pliers until it seated precisely and snugly into the dimple created at the orifice. A
dentine bonding agent (Adper Single Bond, 3M ESPE) was then applied and light-cured.
(a)
(g) (h) (i)
(b)
(d) (e) (f)
(c)
Figure 1 (a) Preoperative photograph: severely broken down tooth 16 (mirror view). (b) Preoperative
radiograph: deep occlusal caries and chronic periradicular periodontitis, tooth 16. (c) Access opening
completed under rubber dam, four orifices detected. (d) Files are prepared with projectors. (e)
Composite built up around projectors to occlusal surface. (f) Files removed leaving projectors in place.
(g) Projectors are removed using H-file. (h) Final result: orifices projected to occlusal surface. (i)
Postobturation radiograph.
Table 1 Details of the dimensions of the PEIGS
Regular
Overall length c. 10.00 mm
Diameter 1 mm from apical end c. 1.20 mm
Large diameter c. 2.00 mm
Tapered lumen full length
Skinny
Overall length c. 13.00 mm
Diameter 1 mm from apical end c. 0.80 mm
Large diameter c. 1.14 mm
Tapered lumen full length
PEIGS, Projector Endodontic Instrument Guidance System.
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International Endodontic Journal, 42, 76–83, 2009 ª 2008 International Endodontic Journal78
The build-up was placed in increments using a hybrid composite (Filtek Z100, 3M ESPE)
and light-cured (Fig. 1e).
Following curing, the files were removed by counter-rotation, leaving the Projectors in
place (Fig. 1f). A high speed, bull-nosed diamond (Mani, Inc) was used to level the occlusal
surface providing ideal endodontic reference points. The final result was a stable coronal
structure with straight-line access into each canal with maximum structural reinforce-
ment. A size 60 Hedstrom hand file was then used to remove the Projectors from the
core, by rotating it clockwise, to engage the flutes in the lumen of each Projector and
withdrawing (Fig. 1g). Thus, a pre-endodontic build-up with individualized access to each
canal was achieved successfully (Fig. 1h).
The original hand file was introduced into each projected orifice and a working length
radiograph was taken. Standard instrumentation was performed to clean and shape the
canals. Interim coronal seal of the canals was simplified by snipping 3 mm from the large
diameter end of each Projector, reinserting them into their respective projected orifices
and then sealing each with Cavit (3M ESPE). At the subsequent visit, the small Cavit seals
were removed with a round bur, and the submerged Projectors were easily removed by
engaging them with a Hedstrom file and withdrawing. Following canal preparation and
filling to the level of the chamber floor (Fig. 1i), the composite in the projected canals was
freshened with a diamond bur (Mani, Inc.) and additional composite resin was bonded
directly over gutta percha to the level of the cavosurface. The pre-endodontic build-up
itself was used as a core and full crown preparation was performed followed by crown
cementation at a subsequent appointment.
Application of this technique created a conical projected orifice which was easily
visualized and accessed and consistently delivered the tip of the endodontic file to the
respective canal whilst maintaining independence of canals from each other. This
technique, once mastered, takes minimal time and greatly enhances treatment of badly
broken down teeth.
Case report 2
A 21-year-old female attended with the complaint of a mildly painful tooth in the
mandibular right posterior region for the past 4 months. Intra-oral examination revealed a
grossly decayed tooth, 46 (FDI). Pulp sensibility tests elicited a negative response. The
preoperative radiograph showed deep occlusal caries involving the pulp space and slight
widening of the periodontal ligament space. The pulp was diagnosed as necrotic,
associated with chronic periradicular periodontitis. Root canal treatment was initiated
using the PEIGS. The procedure for management of this badly broken down tooth was
similar to that described above. Figure 2a–e demonstrates the steps undertaken.
Discussion
The dentist may often be confronted with severely compromised teeth. High quality root
canal treatment and reconstructive procedures are prerequisites to ensure long-term
maintenance of such teeth (Ricucci & Grosso 2006). In such difficult cases, canal
Projectors can facilitate adequate access and preparation of root canals during root canal
treatment. This technique enhances management of complexities including severe
coronal breakdown, tipped/rotated teeth, limited mouth opening and near proximity of
orifices on the chamber floor (Weathers 2004).
In cases of severe coronal breakdown, various methods of isolation have been
suggested, including the use of clamps with apically inclined beaks, the Silker-Glickman
clamp (The Smile Center, Deerwood, MN, USA), or the split-dam technique (Kurtzman
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ª 2008 International Endodontic Journal International Endodontic Journal, 42, 76–83, 2009 79
2004). However, multiple tooth isolation can be less effective than single tooth isolation
and often requires the use of other aids such as floss ligation and/or sealants (Scott 2002).
Occasionally, periodontal or restorative procedures may be necessary to simplify
placement of the rubber dam (Ingle et al. 2002). These procedures include clamping of
anaesthetized attached gingiva, surgical crown lengthening procedure such as gingivopl-
asty or alveoloplasty (Gutmann & Lovdahl 1997) and the composite ‘donut’ technique
(Heydrich 2005). Restorative methods may also be considered to build up the tooth so that
a retainer can be placed properly (Lovdahl & Gutmann 1980, Lovdahl & Wade 1997). A
preformed copper or orthodontic band or a temporary crown may be cemented over the
remaining natural crown. However, the disadvantages include inferior sealing ability,
blockage of canal systems by cement during access opening or instrumentation and
periodontal inflammation if improperly placed/contoured.
(a)
(c) (d)
(b)
(e)
Figure 2 (a): Preoperative photograph: severely broken down tooth 46. (b) Preoperative radiograph:
deep occlusal caries and periradicular periodontitis. (c) Access opening completed under rubber dam,
three orifices detected, matrix band placed. (d) Final result: orifices projected to occlusal surface. (e)
Postobturation radiograph.
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International Endodontic Journal, 42, 76–83, 2009 ª 2008 International Endodontic Journal80
Occasionally, so little tooth structure remains that even band or crown placement is
not possible. In such cases, it becomes necessary to replace missing tooth structure to
facilitate placement of the rubber dam clamp to prevent contamination of the working
field (Lovdahl & Gutmann 1980, Lovdahl & Wade 1997, Scott 2002). The tooth can be
built up with hard, fast-setting temporary cement (e.g. Ketac-Fil, ESPE, Seefeld,
Germany; TERM, LD Caulk, Milford, DE, USA), pin-retained amalgam or composites
(Ingle et al. 2002, Scott 2002). However, these restorative methods are time consuming;
they can impede endodontic access and may require replacement when they are
weakened by endodontic access procedures.
To overcome these challenges, the canal projection technique was developed and
offers the following advantages: (i) it ‘projects’ the canal orifice from the floor of the pulp
chamber to the cavosurface, thereby enhancing visualization and access to the canals, (ii)
permits individualization of canals and therefore can simplify management of canals that
lie in close proximity to each other on the chamber floor, (iii) can allow for ease of
isolation as canal projection essentially replaces missing tooth structure thereby
facilitating clamp retention and thus rendering many structurally debilitated teeth
treatable and (iv) allows files to be inserted easily, particularly nickel–titanium files which
are sometimes difficult to insert into mesial canals as they are unable to retain a bend, as
the canals are no longer obscured by prominent marginal ridges and other visual
obstructions.
The bonded composite coronal build-up decreases coronal leakage (Uranga et al. 1999,
Heling et al. 2002, Schwartz & Fransman 2005) and also reduces the risk of coronal-
radicular fracture during endodontic therapy thereby reinforcing the tooth (Hurmuzlu et al.
2003, Daneshkazemi 2004). Furthermore, the bonded core seals the accessory canals that
exit the chamber floor (Niemann et al.1993, Luglie & Sergente 2001, Haznedaroglu et al.
2003), providing a degree of protection to the chamber floor in cases where extensive
decay has left an area of the floor thin. This prevents leakage of contaminants to the
furcation through what would otherwise be a temporary seal between treatment visits.
The technique can also reinforce perforation repairs by overlaying mineral trioxide
aggregate (MTA) with a bonded resin prior to root canal treatment, preventing
re-aggravation of the perforation site during subsequent procedures (Ford et al. 1995).
Canal projection allows correction of misdirected access cavities by essentially
reconstructing the walls and floors around Projectors which act as ‘internal matrix
barriers’. It insulates files from metallic coronal restorations to facilitate accurate electronic
length determination (Carrotte 2004, Kim & Lee 2004) and also prevents ingrowth of
tissues in cases where cervical tooth structure has been destroyed. The canal projection
process elongates the ‘hydraulic chamber’ of each canal, offering advantages during the
hydraulic condensation of obturating materials, especially whilst using warm vertical
condensation techniques (Glickman & Pettiette 2006).
It should be noted that, as with many useful techniques, canal projection is a technique-
sensitive procedure and may have its limitations; in fact, the obturation may not be limited
to the canal orifices and initially it may be time consuming. However, once mastered, the
technique can be performed with speed and precision, and it can significantly enhance the
balance of treatment, particularly in cases of severe coronal break down.
Conclusion
Management of teeth with minimal coronal structure can be a challenging task when
root canal treatment is required as a part of oral rehabilitation. Coronal leakage, isolation
complexities and risk of interappointment coronal-radicular fracture may be major
contributors to endodontic failure. This case report demonstrates the use of an
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ª 2008 International Endodontic Journal International Endodontic Journal, 42, 76–83, 2009 81
innovative technique, canal projection, as an efficient method for managing these
complex cases.
Conflict of interest
The authors affirm that they have no commercial interest in the materials used or their
method of use as discussed in this manuscript.
Acknowledgements
The authors would like to thank Dr C. John Munce for providing the Projector Endodontic
Instrument Guidance System for undertaking this case report as well as his keen guidance
in the preparation of this manuscript. Thanks to Dr Bhasker Rao, Principal, S.D.M. College
of Dental Sciences, Dharwad, India for his kind cooperation and support.
Disclaimer
Whilst this article has been subjected to Editorial review, the opinions expressed, unless
specifically indicated, are those of the author. The views expressed do not necessarily
represent best practice, or the views of the IEJ Editorial Board, or of its affiliated Specialist
Societies.
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ª 2008 International Endodontic Journal International Endodontic Journal, 42, 76–83, 2009 83
CASE REPORT
Pulp revascularization of necroticbilateral bicuspids using a modifiednovel technique to eliminate potentialcoronal discolouration: a case report
K. Reynolds, J. D. Johnson & N. CohencaDepartment of Endodontics, School of Dentistry, University of Washington, Seattle, WA,
USA
Abstract
Reynolds K, Johnson JD, Cohenca N. Pulp revascularization of necrotic bilateral bicuspids using
a modified novel technique to eliminate potential coronal discolouration: a case report. International
Endodontic Journal, 42, 84–92, 2009.
Aim To present a case report in which the pulp of two bilateral mandibular premolars with
dens evaginatus were revascularized using a modified novel technique to avoid undesired
crown discolouration.
Summary Recently, regeneration of necrotic pulps has become an alternative conser-
vative treatment option for young permanent teeth with immature roots and is a subject of
great interest in the field of endodontics. This novel procedure exploits the full potential of
the pulp for dentine deposition and produces a stronger mature root that is better able to
withstand the forces than can result in fracture. However, the current protocol has
potential clinical and biological complications. Amongst them, crown discolouration,
development of resistant bacterial strains and allergic reaction to the intracanal
medication. In the case presented, a modified technique to avoid undesired crown
discolouration was applied sealing the dentinal tubules of the chamber, thus avoiding any
contact between the tri-antibiotic paste and the dentinal walls.
Key learning points
• Sealing the dentinal tubules of the chamber prevents the undesirable crown discolour-
ation produced by tri-antibiotic medication whilst maintaining the revascularization
potential of the pulp.
• Further research is warranted to seek an alternative infection control protocol capable of
preventing possible allergic reactions and development of resistant strains of bacteria, as
well as a biological material capable of inducing angiogenesis and allow a more predictable
scaffold and tissue regeneration.
doi:10.1111/j.1365-2591.2008.01467.x
Correspondence: Dr Nestor Cohenca, Department of Endodontics, University of Washington,
POB 357448, Seattle, WA 98195 7448, USA (Tel.: 1 206 543 5044; fax: 1 206 616 9085;
e-mail: [email protected]).
84 International Endodontic Journal, 42, 84–92, 2009 ª 2008 International Endodontic Journal
Keywords: crown discoloration, immature permanent tooth, open apex, pulp revascu-
larization, vital pulp therapy.
Received 1 April 2008; accepted 19 July 2008
Introduction
In 1971, Nygaard-Ostby & Hjortdal performed studies that can be considered the
forerunner of pulpal regeneration (Nygaard-Ostby & Hjortdal 1971). The studies were
aimed at determining how periodontal tissue would react, if the entire pulp was removed
from the main canal and the apical part subsequently allowed to be filled with blood.
Skoglund et al. (1978) further demonstrated that in a traumatic avulsion, blood vessels
slowly grow from the apex toward the pulp horn by replacing the necrosed pulp left behind
after the avulsion injury.
Since then, human avulsion case series (Kling et al. 1986) and controlled animal studies
(Cvek et al. 1990a,b, Ritter et al. 2004) have shown radiographic and histological evidence
of successful revascularization of immature permanent teeth after replantation. In this
situation, the necrotic uninfected pulp acts as a scaffold for the in-growth of new tissue
from the periapical area. The absence of bacteria is critical for successful revascularization
because the new tissue will stop at the level it meets bacteria in the canal space (Myers &
Fountain 1974, Yanpiset & Trope 2000). Studies to test the ability of topical antibiotics to
improve revascularization outcomes in experimental avulsions (Yanpiset & Trope 2000,
Ritter et al. 2004) have shown that topical doxycycline and minocycline can improve
radiographic and histological evidence of revascularization in immature avulsed permanent
teeth. Extrapolating from this information, it is hypothesized that once the canal infection
is controlled, it resembles the avulsed tooth that has a necrotic but sterile pulp space. The
blood clot is then introduced so as to mimic the scaffold that is in place with the ischeamic
necrotic pulp in the avulsed tooth and the access cavity is restored with a bacteria-tight
seal. However, in necrotic cases with apical periodontitis it must be recognized that the
vital tissue might not be normal pulp tissue, despite the fact that the root development
continues and dentine maturation occurs. In teeth with open apices and necrotic pulps, it
is possible that some vital pulp tissue and Hertwig’s epithelial root sheath remain. When
the canal is properly disinfected, the inflammatory process reverses and these tissues
may proliferate.
Recently, the concept of revascularization of necrotic pulps regained interest and
became an alternative conservative treatment option for young permanent teeth with
immature roots (Sato et al. 1993, Hoshino et al. 1996, Sato et al. 1996, Iwaya et al. 2001,
Banchs & Trope 2004, Windley et al. 2005, Thibodeau et al. 2007). As well stated by
Windley et al. (2005), revascularization of immature teeth with apical periodontitis
depends mainly on: (a) disinfection of the canal; (b) placement of a matrix in the canal for
tissue in-growth; and (c) a bacterial tight seal of the access opening. Since the infection of
the root canal system is considered to be polymicrobial, a combination of drugs would be
needed to treat the diverse flora. Thus, the recommended protocol combines the use of
metronidazole, ciprofloxacin and minocycline. Hoshino et al. (1996) performed a laboratory
study testing the antibacterial efficacy of these drugs alone and in combination against the
bacteria of infected dentine, infected pulps and periapical lesions. Alone, none of the
drugs resulted in complete elimination of bacteria. However, in combination, these drugs
were able to consistently sterilize all samples. In addition, a study by Sato et al. (1996)
found that this drug combination was effective in killing bacteria in the deep layers of root
canal dentine.
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85ª 2008 International Endodontic Journal International Endodontic Journal, 42, 84–92, 2009
This novel procedure exploits the full potential of the pulp for dentine deposition and
produces a stronger mature root that is better able to withstand fracture but has the
potential for clinical and biological complications. Amongst them, crown discolouration
(Windley et al. 2005), development of resistant bacterial strains (Greenstein & Polson
1998, Eickholz et al. 2002, Slots 2002) and allergic reaction to the intracanal medication
(de Paz et al. 1999, Hausermann et al. 2005, Jappe et al. 2005, Isik et al. 2007, Madsen
et al. 2007). Although coronal discolouration is not often reported in the literature in
association with the use of this tri-antibiotic medication, it is believed that the marked
discolouration may to be related to the use of minocycline. Kim et al. (2000) demonstrated
that Ledermix (Lederle Pharmaceuticals, GMBH Wolfratshausen, Germany), an intracanal
medication containing tetracycline, caused discolouration of immature teeth in a greater
degree than in mature teeth.
A case report is presented in which the pulps of bilateral mandibular premolars became
necrotic because of dens evaginatus and were revascularized using a modified novel
technique to avoid undesired crown discolouration.
Case report
An 11-year-old Asian girl was referred to the graduate endodontic clinic by her dentist for
evaluation and root canal treatment of her mandibular second premolars. The medical
history was non-contributory. A review of the dental history revealed that the patient had
sought dental care 3 months prior because of swelling and pain in the mandibular left
premolar region. The patient was prescribed penicillin VK 1000 mg daily by her general
dentist. The pain and swelling subsided within a week. Upon clinical examination, an
occlusal tubercle consistent with dens evaginatus (Fig. 1a,b) was diagnosed. Intraoral
sinus tracts, buccal to the mandibular left and right second premolars were present
(Fig. 1c,d). No caries were clinically detected. Pulp sensibility tests using 1, 1, 1,
2-tetrafluoroethane (Endo-Ice; Hygenic Corp., Akron, OH, USA) produced no response
from either mandibular second premolars whilst the adjacent mandibular first molars and
premolars responded to cold without lingering. Neither mandibular second premolars
were sensitive to percussion or palpation. Periodontal probing affirmed normal attachment
with no probing depths >3 mm and normal physiological mobility. No crown discolouration
was observed.
Radiographically both mandibular second premolars had a similar appearance, with
widened periodontal ligament space, incomplete root formation and diffuse periapical
radiolucencies 6 · 6 mm in size (Fig. 2a,b). No carious lesions were diagnosed (Fig. 2c)
and the root development appeared arrested with wide open apices in both mandibular
second premolars. A gutta-percha point was used to trace the sinus tract and a periapical
radiograph taken, demonstrating the association between the drainage and the periradic-
ular radiolucency (Fig. 2d).
Based on the results of clinical and radiographic examination, the pulpal and
periradicular diagnosis of the mandibular left and right second premolars was determined
as pulpal necrosis with chronic suppurative periradicular periodontitis. Taking into
consideration the stage of root development, the maturation of the dentinal walls and
the wide-open apices, the treatment plan included pulp revascularization of both
mandibular second premolars. After a comprehensive discussion of the risks, complica-
tions and possible outcomes of this treatment, parental consent was obtained.
Following administration of local anaesthesia, the mandibular left second premolar was
isolated with rubber dam. Under a dental-operating microscope, access preparation
was performed and a single orifice with a wide canal was revealed. No purulent exudates
or haemorrhage were observed in the chamber (Fig. 3a). Length was estimated
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86 International Endodontic Journal, 42, 84–92, 2009 ª 2008 International Endodontic Journal
radiographically using a size15 K-file. The selection of the file size was made to avoid any
damage to the canal walls. The irrigation protocol included a slow and careful irrigation of
20 mL of 6% sodium hypochlorite, 2 mm back from working length. This was followed by
a 5 mL rinse of saline and then a final irrigation of 10 mL of 2.0% chlorhexidine gluconate
(Vista Dental, Racine, WI, USA).
A modification of the current clinical protocol (Sato et al. 1996, Banchs & Trope 2004)
was established to avoid crown discolouration. This novel approach seals the dentinal
tubules of the chamber, thus avoiding any contact between the tri-antibiotic paste and
the dentinal walls. The inner surfaces of the coronal access were etched for 20 s with
35% phosphoric acid (Ultra-Etch; Ultradent, South Jordan, UT, USA) and rinsed. Bonding
agent was applied (Single Bond 3M, Minneapolis, MN, USA) to the etched surfaces and
cured for 20 s. Then, a Root Canal Projector (CJM Engineering Inc., Santa Barbara, CA,
USA) with a size 20 K-file inside the projector was placed into the prepared access to
maintain patency. The space between the projector and the coronal dentine was sealed
with flowable composite (PermaFlo DC; Ultradent, South Jordan, UT, USA) and light-
cured for 30 s (Fig. 3b). The projector was then removed by engaging it with a Hedstrom
file.
The tri-antibiotic paste was prepared immediately prior to treatment by mixing 250 mg
of Ciprofloxacin, 250 mg of Metronidazole and 250 mg of Minocycline with sterile water
(Fig. 3c). A 20G needle was set 2 mm short of working length and used to introduce the
medication into the canal using a backfill approach up to the level of the cemento-enamel
junction (CEJ) (Fig. 3d). The tooth was then temporarily sealed with a cotton pellet and
Cavit (3M ESPE, Seefeld, Germany).
One month later, the patient presented with localized swelling and pain on her
mandibular right quadrant associated with the mandibular right second premolar. The
Figure 1 (a,b) Clinical photographs showing an occlusal tubercle consistent with dens evaginatus in
both mandibular second premolars. (c,d) An intraoral localized swelling buccal to the mandibular left
and right second premolars is noted.
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87ª 2008 International Endodontic Journal International Endodontic Journal, 42, 84–92, 2009
swelling was visible extraorally along the lower border of the mandible in the
submandibular space, tender to palpation and non-fluctuant. The patient’s temperature
was 36.6 �C. Under local anaesthetic and rubber dam isolation, the mandibular right
second premolar was accessed for treatment. Upon access, no purulent exudate was
noted and only some minor haemorrhage. After working length was determined, the canal
was carefully irrigated with 10 mL of 6% sodium hypochlorite up to 2 mm from working
length at which time the access was sealed with a cotton pellet and Cavit as a temporary
restoration. In case of persistent pain, the patient was instructed to take ibuprofen
200 mg. Incision and drainage was not indicated, as the draining sinus tract was still
present and the swelling was non-fluctuant.
At the same appointment, it was noted that the mandibular left second premolar was
asymptomatic and was not sensitive to palpation and percussion. The sinus tract
associated with the mandibular left second premolar had healed.
Four-days later the swelling was significantly reduced, as well as the patients’ complain
of pain in the mandibular right quadrant. The sinus tract stoma associated with the
mandibular right second premolar was still present. At this appointment it was decided to
continue treatment of the mandibular left second premolar as previously planned. Under
local anaesthesia and rubber dam isolation, the tooth was re-accessed. No purulent
drainage or haemorrhage was noted upon access and the tri-antibiotic paste was removed
with 6% sodium hypochlorite with the irrigation needle tip 2 mm short of the working
(a)
(c)
(b)
(d)
Figure 2 (a,b) Radiographic examination demonstrated incomplete root formation and diffuse
periapical radiolucencies of 6 · 6 mm in size in both mandibular second premolars. (c) No carious
lesion was diagnosed. (d) A gutta-percha point was used to trace the sinus tract and a periapical
radiograph was taken, demonstrating the association between the drainage and the periradicular
radiolucency.
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88 International Endodontic Journal, 42, 84–92, 2009 ª 2008 International Endodontic Journal
length. With the root canal infection controlled, the regenerative process was initiated. A
sterile size 20 K-File was introduced 2 mm past the working length to stimulate bleeding
and create a biological scaffold for pulpal regeneration. The intracanal haemorrhage was
controlled below the CEJ by applying pressure with a sterile saline-soaked cotton pellet
until a clot was established. ProRoot grey MTA (Dentsply Tulsa Dental, Johnson City, TN,
USA) was then mixed with sterile water and carefully placed above the blood clot up to the
level of the CEJ. The access was sealed with a moist cotton pellet and Cavit. At the same
appointment, the mandibular right second premolar was anaesthetized and isolated with
rubber dam. No purulent drainage or haemorrhage was observed upon access of the
mandibular right second premolar. At this time, the same clinical protocol used to treat the
mandibular left second premolar was used on the mandibular right second premolar.
Using the same novel technique mentioned previously to avoid discolouration, flowable
composite was applied to the coronal dentine sealing the dentinal tubules preventing
contact with the tri-antibiotic paste. The tri-antibiotic dressing was placed into the canal
with a syringe set at 2 mm from the working length. The access was then sealed with a
cotton pellet and Cavit.
Two weeks following the last appointment, the patient returned asymptomatic and
without swelling or sinus tract stomas on either side of the mandible. Under local
anaesthesia and rubber dam isolation in the mandibular left quadrant, the temporary
restoration was removed from the mandibular left second premolar and the coronal
(a)
(c)
(b)
(d)
Figure 3 (a) Mandibular left second premolar was accessed under a dental-operating microscope,
without evidence of purulent exudates or haemorrhage. (b) A Root Canal Projector with a size 20 K-file
inside the projector was placed into the prepared access to maintain patency. The space between the
projector and the coronal dentine was sealed with flowable composite and cured for 30 s. (c) The tri-
antibiotic paste was prepared immediately prior to treatment and loaded in a syringe with a 20G
needle and a rubber stopper. (d) The canal was dressed using a backfill approach up to the level of the
cemento-enamel junction (CEJ) and the tooth was then temporarily sealed. Notice the flowable
composite sealing the access walls up to the level of the CEJ.
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89ª 2008 International Endodontic Journal International Endodontic Journal, 42, 84–92, 2009
access refined, cleaned and restored with resin-bonded composite (Prisma TPH; Dentsply
Culk, York, PA, USA).
Four weeks after the tri-antibiotic medication was placed on the mandibular right
second premolar, the patient was asymptomatic and without swelling or sinus tract
stomas on either side. Under local anaesthesia and rubber dam isolation, the tooth was
treated using the same clinical protocol used for the mandibular left second premolar.
Briefly, sodium hypochlorite irrigation was used for removal of the tri-antibiotic paste
followed by stimulation of haemorrhage, clot formation and MTA placement. The tooth
was then temporized and the patient was rescheduled for the final composite restoration
which was place 2 weeks later without incident or change in symptoms.
During the 18-month follow-up period the patient remained asymptomatic. Clinically,
both mandibular second premolars responded within normal limits to cold test using 1,
1, 1, 2-tetrafluoroethane. No tenderness to percussion or palpation was noted and the
periodontal examination revealed no pocket depths over 3 mm and normal physiological
mobility. The radiographs demonstrated evidence of periradicular bone healing and
significant root development with maturation of the dentine as compared with the
preoperative radiographs (Fig. 4a,b). Clinically, the mandibular right second premolar
teeth showed no change in shade or colour (Fig. 4c), although mandibular left second
premolar revealed a slight cervical discolouration possibly related to the use of grey
MTA (Fig. 4d).
Discussion
An immature tooth with early irreversible pulp involvement presents with thin divergent or
parallel dentinal walls. This situation creates clinical challenges in disinfection, and as a
result, affects the long-term outcome of the treatment. Traditionally, calcium hydroxide
has been used as the intra-canal medicament in apexification procedures. However,
because of its high pH it will cause necrosis of tissues that can potentially differentiate into
new pulp. Moreover, even if rendered successful, apexification procedures will leave a
short root with thin dentinal walls with a high risk of root fracture.
Revascularization of a pulp-like tissue for dentine deposition will allow further
development of the root and dentinal structure with a better long-term prognosis. As
shown in the present case, clinical and radiographic evaluation at 6-month intervals is
stressed after revascularization therapy, so as to assess pulp vitality and progression of
root development. Current vitality tests still depend on neurological stimulation and its
reliability on immature teeth is considered questionable (Fulling & Andreasen 1976, Fuss
et al. 1986). The radiographic diagnosis of periapical pathosis may also become difficult in
immature teeth because of the normal radiolucency of the developing root sheath which
occurs apically as the root matures. Comparison of root formation with the contralateral
teeth should always be performed to evaluate treatment outcome.
If crown discolouration occurs, treatment by intracoronal bleaching with sodium
perborate should be attempted. In addition, the use of white MTA instead of grey MTA
should also be considered. The modified protocol described in the present article is an
attempt to avoid the undesired crown discolouration. It also describes a safer and more
reliable technique for antibiotic dressing using a 20G needle with a backfill approach. This
novel approach prevents the undesirable crown discolouration produced by the tri-
antibiotic medication, whilst maintaining the revascularization potential of the pulp. Taking
in consideration the importance of aesthetics, this technique could be consider for all
anterior teeth in which the use of the tri-antibiotic paste is indicated for revascularization
purposes. Further research is warranted to seek an alternative infection control protocol
capable of preventing possible allergic reactions and development of resistant strains of
CASE
REPORT
90 International Endodontic Journal, 42, 84–92, 2009 ª 2008 International Endodontic Journal
bacteria, as well as a biological material capable of inducing angiogenesis and allow a more
predictable scaffold and tissue regeneration.
Disclaimer
Whilst this article has been subjected to Editorial review, the opinions expressed, unless
specifically indicated, are those of the author. The views expressed do not necessarily
represent best practice, or the views of the IEJ Editorial Board, or of its affiliated Specialist
Societies.
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CASE
REPORT
92 International Endodontic Journal, 42, 84–92, 2009 ª 2008 International Endodontic Journal