An in Vitro Evaluation of Microtensile Bond Strengths of Two Adhesive Bonding Agents to Residual...

8/10/2019 An in Vitro Evaluation of Microtensile Bond Strengths of Two Adhesive Bonding Agents to Residual Dentine After C

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An in vitro evaluation of microtensile bond strengths of two

adhesive bonding agents to residual dentine after caries

removal using three excavation techniques

A. Banerjee *, S. Kellow, F. Mannocci, R.J. Cook, T.F. Watson

Kings College London Dental Institute, KCL, United Kingdom

1. Introduction

The increasing evidence and popularity of the minimally

invasive operativemanagement of carious dentine hasbrought

into question the apparent necessity for complete caries

removal when restoring a cavitated lesion in a patient.1,2 The

superficial necrotic zone of caries-infected dentine that

harbours the core bacterial biomass should be excavated

leaving only residual caries-affected dentine lining the

cavity with sound enamel marginsand dentine adjacent to the

j o u r n a l o f d e n t i s t r y 3 8 ( 2 0 1 0 ) 4 8 0 4 8 9

a r t i c l e i n f o

Article history:

Received 21 January 2010

Received in revised form

22 February 2010

Accepted 2 March 2010

Keywords:

Dentine

Caries

Excavation

Microtensile bond strength

Dentine bonding agent

Confocal microscopy

Composite

Silorane

CarisolvTM gel

Biosolv

a b s t r a c t

Objectives: To assess amounts of residual dentine retained after using three excavation

techniques; the microtensile bond strengths (mTBS) to residual dentine, comparing etch-

rinse vs. self-etching adhesives.

Methods: 42 carious molars were subdivided (N= 21) dependent upon adhesive/composite

system (Adper Scotchbond 1XT and Filtek Supreme vs. Filtek Silorane adhesive and com-

posite). Dividing into three (N= 7), dependent upon caries excavation technique employed

(hand vs. chemo-mechanical: CarisolvTM gel vs. experimental enzymatic gel (SFC-V)), caries

removalwas assessed using visual/tactile criteria and in situ autofluorescence (AF) confocal

fibre-optic micro-endoscopy (CFOME). Post-restoration/four-week hydrated storage, four

0.9 mm2 beams per tooth underwent mTBS testing/microscopic analysis of fractured sur-

faces. Three cavities from each excavation group were analysed using SEM.

Results: SEM revealed surface roughness with smear layer occluding tubuleorifices in hand-excavated samples and a reduced, variable smear layer for both chemo-mechanical sys-

tems. CFOME AF assessment indicated hand excavation left sound dentine, CarisolvTM left

affected dentine and SFC-V slightly under-prepared clinically. MeanmTBS values from etch-

rinse samples (27 MPa (SD 3.9), hand; 22 MPa (SD 5.1), CarisolvTM; 26 MPa (SD 4.4), SFC-V)

showed statistical differences between hand and CarisolvTM groups. Mean mTBS data for

self-etch samples (22 MPa (SD 3.3), hand; 27 MPa (SD 6.1), CarisolvTM; 25 MPa (SD 4.7), SFC-V)

showed significant differences between hand and CarisolvTM, and hand vs. SFC-V. Failure

loci distribution in etch-rinse samples was between dentineadhesive, within adhesive and

within composite whereas self-etch samples exhibited failure predominantly between

adhesive and composite.

Conclusions: Data indicated that all null hypotheses were disproved.

# 2010 Elsevier Ltd. All rights reserved.

* Corresponding author at: Kings College London Dental Institute, KCL, Floor 26, Tower Wing, Guys Dental Hospital, London Bridge,London. SE1 9RT. Tel.: +44 0207 188 1577 7486; fax: +44 0207 188 1577 7486.

E-mail address:[email protected](A. Banerjee).

a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m

journal homepage: www.intl.elsevierhealth.com/journals/jden

0300-5712/$ see front matter # 2010 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jdent.2010.03.002
mailto:[email protected]://dx.doi.org/10.1016/j.jdent.2010.03.002http://dx.doi.org/10.1016/j.jdent.2010.03.002mailto:[email protected]


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enameldentine junction (EDJ).3,4 This will enable the best

peripheral seal to be achieved with the current adhesive

dentine bonding systems, as long as sufficient moisture

control can be obtained.

Identification of the histological transition zone between

infected and affected dentine is difficult to assess both

clinically and in the research laboratory. Change in colour is

not a good indicator as the gradual bacterial and histologicalchanges are not consistently colour-dependent.5 Caries

detector dyes based on propylene glycol were developed in

order to highlight alterations in dentine collagen structure but

publications have shown that clinical and laboratory results

produced are open to considerable user-interpretation.68 The

relative hardness/tactility of the dentine has clinical validity;9

sound dentine is scratchy to a sharp dental explorer, infected

dentine has a soft, mushy consistency and affected dentine

falls in between, often simultaneously scratchy and tacky, but

again this method of identifying the transition zone is fraught

with operator subjectivity.4 The autofluorescence (AF) of

carious dentine has been proposed as a potential marker for

that carious dentine requiring excavation but originally, theconfocal microscopy equipment used to detect the AF

signature could only be useful in laboratory research experi-

ments where extracted tooth sections could be prepared.1013

More recently, this technology has been developed into a

confocal fibre-optic micro-endoscope (CFOME) which can

operate in situ during active caries excavation in whole teeth,

so providing immediate numerical, objective feedback of the

AF quality of the residual carious dentine.14

The selective removal of caries-infected dentine is not

easilyachieved with the mostpopular current operativecaries

excavation techniquesthe rotary bur and spoon-shaped hand

excavator. This is due to their relative tactile insensitivity and

operator variability in use leading to varying quantities oftissue removed.13 Chemo-mechanical agents have been

developed to be used in conjunction with their own hand

instruments and evidence exists to show that their careful use

may offer some element of selectivity between the infected

and affected dentine. One such gel system currently available

for clinical use is based upon the controlled activity of sodium

hypochlorite on dentine collagen, used with abrasive hand

instruments (CarisolvTM gelOraSolv AB, Gothenburg, Swe-

den).13,15 Another, based upon the enzymatic action of pepsin

in an acidic environment (SFC-V, Biosolv, 3MESPE AG,

Seefeld, Germany) is at the clinical trial phase of its

development but shows promise. Another factor to consider

in terms of restoring the resulting cavity with adhesive

materials, is the final dentine surface characteristics (surface

roughness, presence of smear layer) which can affect the final

bond and seal achieved by adhesive systems.16,17

In terms of factors affecting the long term success of

adhesive restorations, the marginal integrity/potential for

microleakage at the tooth-restoration interface due to a poorseal, appear high on the list.18,19 This in turn is closely

associated with the quality of the bond achieved by modern

dentine bonding systems. Current adhesives tend to fall

broadly into one of two groupsthe etch-and-rinse systems

which involve a separate etch phase with 37% orthopho-

sphoric acid on both enamel and dentine for approximately

20 s prior to placement of the primer and bond (adhesive), or

the self-etching systems which incorporate the acidic moi-

eties within the primer phase of the bonding system, which

are incorporated into the final adhesive layer. There is

evidence extolling the potential virtues of each system in

the strength of the bond achieved to varying dental sub-

strates,2022 but less conclusive evidence when specificallyconsidering the bond to caries-affected dentine.21,2329

Therefore the null hypotheses to be investigated in this

study were:

1. There are no differences in the amount and quality of

carious dentine excavated by three different clinical hand

excavation techniques (CarisolvTM gel, SFC-V and hand

excavation).

2. Using three different caries excavation techniques (Car-

isolvTM gel, SFC-V and hand excavation) has no effect on

adhesive bond strengths to the residual carious dentine,

comparing total-etch and self-etching dentine bonding

systems.3. Using three different caries excavation techniques (Car-

isolvTM gel, SFC-V andhand excavation) hasno effect on the

failure mode and loci of failure when bonding to the

residual carious dentine, comparing total-etch and self-

etching dentine bonding systems.

2. Materials and methods

The materials used in this study are outlined inTable 1. With

Guys Hospital research ethics approval (04/Q0704/57), 51

extracted, human cavitated carious molars, stored in water for

Table 1 Materials used in the study.

Brand name Manufacturer Batch no. Type/constituents

Adper Scotchbond 1XT 3MESPE AG, Germany 20050711 Total-etch dentine bonding agent

Filtek Supreme 3MESPE AG, Germany 20030322 Hybrid resin composite

Filtek Silorane adhesive 3MESPE AG, Germany Experimental sample Self-etch dentine bonding agent

Filtek Silorane 3MESPE AG, Germany 203905 Low-shrink siloxaneoxirane composite

CarisolvTM gel Orasolv AB, Sweden 06009 Chemo-mechanical caries removal gel

(0.5%, w/v sodium hypochlorite; 0.1 M

glutamic acid/leucine/lysine, sodium

chloride, sodium hydroxide,

carboxymethycellulose

SFC-V (Biosolv) 3MESPE AG, Germany 0540 Experimental chemo-mechanical caries

removal gel (pepsin, phosphoric acid/sodium

biphosphate buffer)

j o u r n a l o f d e n t i s t r y 3 8 ( 2 0 1 0 ) 4 8 0 4 8 9 481


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no longer than four weeks, were selected and 42 of these were

randomly divided into two experimental groups (N= 21),

according to the type of adhesive restorative system used.

Teeth in one group would be restored using an etch-and-rinse

bonding agent plus a nano-hybrid resin composite (Adper

Scotchbond 1XT with Filtek Supreme resin composite

(3MESPE, Seefeld, Germany)) whilst those in the other would

be restored with self-etching Filtek Silorane bond and low-shrink Filtek Silorane composite (seeTable 1). Each of these

groups was further subdivided into three subsets, dependent

upon the caries excavation technique employed: conventional

hand excavation using a spoon-shaped hand excavator,

CarisolvTM gel and SFC-V Biosolv (N= 7 in each).

2.1. Caries excavation

Under 3 magnification dental loupes, a tungsten carbide

fissure bur in an air-turbine handpiece (No. 57, Smartbur,

Bridgewater Corners, USA) was used to remove any overlying,

undermined enamel, so exposing the full extent of occlusal

carious dentine including a periphery of sound dentine. Seventeeth from each of the two main groups underwent clinical

caries excavationusing a spoon-shaped hand excavator, using

operator-dependent tactility to determine the endpoint of

caries excavation (seeFig. 1). A separate seven teeth in each

group underwent caries excavation using CarisolvTM gel as per

manufacturers instruction, using an abrasive metal mace-tip

instrument provided. The pre-mixed gel was introduced into

the cavity for 40 s prior to agitating the mixture against the

dentine using the mace-tip instrument. Once the gel had

become cloudy with a muddy consistency, it was rinsed

away and a second fresh mix of gel was applied and further

agitated. Excavation was deemedcomplete when the gel failed

to become cloudy and the cavity was checked with a dental

probe for hardness. The remaining seven teeth in each group

underwent chemo-mechanical caries removal using SFC-V

solution, with the same mace-tip instrument. The SFC-V was

introducedinto the cavityand wasimmediately agitated usingthe mace-tip hand instrument and washed away with further

subsequent applications until the gel did not remove any

further dentine and did not become turbid (see Fig. 2).

2.2. Scanning electron microscopy (SEM)

The remaining nine teeth with cavitated occlusal caries were

subdivided into three groups (N= 3) according to the caries

excavation technique employed (see above). After excavation,

rinsing and drying the final cavities, addition-cured light body

silicone impressions were taken (President, Coltene AG,

Switzerland) and from these, epoxy resin replicas created,

gold sputter-coated and imaged using SEM (Hitachi S520-Hitachi Scientific Instruments, Wokingham, Berks., UK),

12 kV).

2.3. CFOME AF measurements

The confocal laser imaging system (Cellvizio1 Mauna Kea

Technologies, Paris, France) was configured with a 600 mm

diameter plane-ended mini-o1 surface contact optical fibre

bundle objective probe (015 mm focal plane depth,


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lateral resolution, approximately 15 mm axial resolution and

no distal optical element). After enamel preparation, the pre-excavation autofluorescence of the carious dentine in all

samples was recorded using 488 nm laser illumination. AF

wavelengths, detected via the same coherent fibre elements,

were delineated from reflected illumination wavelengths

using>505 nm long-pass filtration. At the full imaging frame

rate of 12 fps, the individual non-contiguous fibre spot images

were recorded in real-time and reconstructed as micro-

endoscopic real-time fluorescence maps with ten separate

readings mapped across the occlusal extent of each lesion. For

each field of view (600 mm), the supplied software calculated

the mean numerical fluorescence intensity (arbitrary units).

As there was no contrast in a fully white (i.e.saturated) image,

and no data in a fully black field (sound dentine), the

numerical measure of greyscale represented the degree of

AF saturation of the image. The confocal fibre was peroxide-bleached (standardised manufacturer protocol) between every

reading to eliminate fluorescent debris transfer between

measurement sites and between readings from a site. A

subsequent reading was only taken when no fluorescence was

recorded from the probe tip in air, representing a zero-

calibration. Readings taken from the exposed sound dentine

acted as internal sample controls. A pilot study confirmed that

contact imaging AF measurements from both sound and

carious dentine samples showed no discernable AF data

variation with darkness to bright daylight ambient conditions.

Ten post-excavation CFOME readings were finally mapped

from the remaining dentine cavity surface following the

protocol outlined above.

Fig. 2 Caries removal using chemo-mechanical CarisolvTM gel. (a) The original occlusally cavitated carious lesion in a

mandibular molar. (b) The full extent of the carious dentine and sound margin exposed after enamel removal. (c) Clear gel

applied and left for 40 s before (d) agitation against the dentine using a mace-tip abrasive hand instrument. (e) Turbidity of

the gel prior to rinsing and (f) the final excavation when no further caries is dissolved by the gel, leaving affected dentine.



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2.4. Cavity restoration and microtensile testing

After caries excavation, the 21 samples in each group were

restored either with Adper Scotchbond 1XT/Filtek supreme

resin composite or Filtek Siloraneadhesive/Silorane composite,as per manufacturers instruction. After hydrated four-week

storage,the teethwere firstsectioned through the restoration in

a mesio-distal longitudinal plane using a low speed water-

cooled diamond saw (Labcut, Agar Scientific, Stansted, UK). A

perpendicular section to the adhesivetooth interface followed

to obtain beams (0.9 mm 0.9 mm wide; 57 mm long), each

consisting of composite, adhesive and dentine. Twenty-five

beams were produced from each of the six excavation sub-

groups. These were fixed with cyanoacrylate glue (Loctite1,

Henkel, Hatfield, UK) to two surfaces on a linear actuator-

driven, offset micro-tensile testing device (SMAC, Horsham,

UK), and stressed at a crosshead speed of 1 mm/min until

failure. The micro-tensile bond strength (mTBS) was expressedin MPa, as derived from dividing the imposed force (N) at the

time of fracture by the bond area (mm2).

In order to evaluate the failure mode of the beam

specimens after fracture, each sample was reassembled,

fixed flat on a glass slide using PlasticineTM and placed on the

stage of a confocal microscope (Noran Tandem Scanning

Microscope, Madison WI, USA). Samples were illuminated

with a mercury arc lamp andexamined using a 20/0.80 NA oil

immersion objective lens in conjunction with a 10 eyepiece

(Olympus, Japan). The failure modeon one external surface of

each beam was determined visually and recorded (see

Table 2) and the sample rotated until all four sides had been

analysed.

2.5. Statistics

The microtensile bond strengthdata was statistically analysed

using KaplanMeier survival analysis with Sidaks adjustment

for multiple comparisons. Significance was set at p < 0.01.

3. Results

3.1. SEM evaluation

Representative micrographs for the hand excavation samples

are shown in Fig. 3, CarisolvTM gel excavation, Fig. 4 and SFC-V(Biosolv),Fig. 5. Low magnification SEMs showed flaky, rough

surfaces with all excavation modalities, but subjectivelyworse

in the hand excavation group. At higher magnification, a

consistent smear layer was detected in the hand excavation

group causing plugs to form within the tubular orifices

(Fig. 3b). Both chemo-mechanical techniques produced a

reduced and more inconsistent smear layer with large areas

of open tubular orifices in the CarisolvTM group (Fig. 4) and a

greater mixture of open and closed tubules in the SFC-V

(Biosolv) group (Fig. 5).

3.2. CFOME AF measurements

Table 3outlines the AF numerical data from the samples from

each experimental group, pre- and post-excavation. Consis-

tently elevated AF data was produced from the original caries-

infected dentine pre-excavation across all experimental

groups. Significant reduction in the AF data post-excavation

was apparent in all experimental groups indicating the

Table 2 The codes used to analyse the mode of failureand loci of failure on the external surfaces of the sticksamples having undergone microtensile testing.

Code Failure mode/locus

1 Cohesivein dentine

2 Adhesivebetween dentine/ad-

hesive layer

3 Cohesivewithin the adhesivelayer

4 Adhesivebetween adhesive

layer/composite

5 Cohesivewithin composite

The proportion of each surface to undergo varying modes of failure

was also considered. The coding relates toFig. 8.

Fig. 3 Scanning electron micrographs of epoxy resin replicas of the dentine surface remaining after conventional hand

excavation. (a) 1.0k magnification showing smearing of the dentine surface and tubule occlusion. (b) 5.0k magnification

showing a structureless smear film and plugs within the tubule orifices.



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removal of infected dentine. Hand-excavated samples showed

the greatest reduction in AF (to a mean value of 69) indicating

potential over-preparation into histologically sound dentine.

Out of the two chemo-mechanical groups tested, CarisolvTM

gel excavation tended to remove a more consistent amount of

dentine (smaller standard deviation; mean AF value 130) and

SFC-V tended to leave more residual carious dentine behind

(mean AF value 269).

Fig. 4 Scanning electron micrographs of epoxy resin replicas of the dentine surface remaining after CarisolvTM gel

excavation. (a) 800T magnification showing a dentine surface with open tubule orifices. (b) 2.0k magnification showing a

lack of smear layer and opened tubules.

Fig. 5 Scanning electron micrographs of epoxy resin replicas of the dentine surface remaining after SFC-V (Biosolv) gel

excavation. (a) 1.0k magnification showing an area of smear plug-filled tubular orifices. (b) 1.0k magnification showing an

area of opened tubular orifices.

Table 3 Mean AF data (arbitrary units) plus standard deviations (SD) for each experimental group, before and after cariesexcavation, measured using CFOME.

Scotchbond 1XT/Filtek Supreme (N= 21) AF pre-excavation SD AF post-excavation SD

Hand (N= 7) 1897.50 682.38 61.76 30.82

CarisolvTM (N= 7) 2241.86 533.75 126.11 37.53

SFC-V Biosolv (N= 7) 2064.00 592.42 264.71 79.30

Filtek Silorane bond/composite (N= 21)

Hand (N= 7) 1704.00 620.18 60.79 30.53

CarisolvTM (N= 7) 2317.86 594.57 134.49 38.43

SFC-V Biosolv (N= 7) 2200.00 486.19 274.00 88.42

Ten readings per tooth both pre- and post-excavation were analysed. CFOME was calibrated against ambient lighting conditions and internal

sound dentine controls (0 reading indicates no fluorescent signal).



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3.3. Microtensile bond strengths

In the etch-and-rinse group the mean value of the micro-

tensile bond strengths obtained after four weeks hydrated

storage was 27 MPa (SD 3.9) for hand excavation, 22 MPa (SD

5.1) for CarisolvTM and 26 MPa(SD 4.4) for SFC-V.Thisdatawas

analysed using KaplanMeier survival analysis (Fig. 6) with

Sidaks adjustment for multiple comparisons which indicated

that there was a significant global difference between the

survival curves (p= 0.01). Sidaks multiple comparison indi-

cated that there was no significant difference between hand

excavation and SFC-V subgroups or between CarisolvTM and

SFC-V. There was however, a significant statistical difference

in the microtensile bond strengths between the hand

excavation and CarisolvTM groups.In the case of the self-etch group, the mean value of the

bond strengths obtained was 22 MPa (SD 3.3) for hand

excavation, 27 MPa (SD 6.1) for CarisolvTM and 25 MPa (SD

4.7) for SFC-V. Again, the bond test data was analysed using

the above-mentioned statistics (Fig. 7), where Sidaks multiple

comparison indicated that there was no significant difference

between the CarisolvTM and SFC-V subgroups. There was a

significant difference between hand excavation and Cari-

solvTM, and between hand excavation and SFC-V.

3.4. Analysis of failure modes

The locus and type of failure was described and coded inTable 2 and the distribution of failure, examined from the four

external surfaces of each matchstick sample, have been

graphically illustrated inFig. 8. In the etch-and-rinse samples,

an even distribution of failure types 2, 3 and 5 were notedwith

a small number of cohesive dentine failures across the sub-

groups (type 1). In the self-etch Silorane samples, adhesive

failures between the bond and composite predominated (type

4) with further even distributions of cohesive failures within

the bond layer and composite, respectively. There were fewer

adhesive failures between dentine and the bond layer (type 2)

in the self-etch Silorane samples than the total-etch Scotch-

bond samples, independent of the excavation techniques

used.

Fig. 6 Microtensile bond strength data for the Scothbond

1XT/Filtek Supreme experimental group (H, hand

excavation; C, CarisolvTM; and B, SFC-V Biosolv). Mean

data for each sub-group calculated from the 50% survivalrate. Sidaks multiple comparison analysis indicated a

significant difference between hand excavation and

CarisolvTM groups.

Fig. 7 Microtensile bond strength data for the Filtek

Silorane bond/composite experimental group (H, hand

excavation; C, CarisolvTM; and B, SFC-V Biosolv). Mean

data for each sub-group calculated from the 50% survival

rate. Sidaks multiple comparison analysis indicated a

significant difference between hand excavation and each

of the two chemo-mechanical excavation groups.

Fig. 8 Graph showing the % distribution of the five

different failure modes (Table 2) in each of the

experimental groups (SB, Scotchbond/Supreme samples;

SA, Silorane bond/composite samples; H, hand

excavation, C, CarisolvTM, B, SFC-V Biosolv). From the

data it can be seen that the predominant failure in the self-

etched Silorane samples was type 4 (between the adhesive

layer and the composite) whereas for the Scotchbond

total-etch samples, there were even proportions of

predominantly type 2, 3 and 5 failures.



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4. Discussion

This study aimed to investigate a number of null hypotheses

simultaneously within the same natural carious tooth

samples, so enabling clinical relevance to emerge from an

in vitro study. A single trained operator was used in order to

minimise inter-operator variability in this study, but the

potential for clinical variation in the use of these technologiesmight be worthy of future investigation.

There are no differences in the amount and quality of

carious dentine excavated by three different clinical hand

excavation techniques (CarisolvTM gel, SFC-V and hand

excavation).

Two chemo-mechanical agents were compared against

each other and conventional hand excavation in this study.

Caries removal was guided by the self-limiting nature of the

technique and/or the hardness of the dentine remaining.

Using novel CFOME technology to measure the AF level of

initial and residual caries, enabled an objective, in situ

assessment of the type of dentine remaining and the quality

of that tissue excavated. A previous study has calibrated thefluorescent saturation intensity levels for infected, affected

and sound dentine against its microhardness.14 The data

presented here indicated that hand excavation tended

towards over-preparing the dentine, leaving histologically

sound cavity walls (AF < 100; mean reading 69). Both chemo-

mechanical systems, arguably more self-limiting due to the

collagenolytic action of the sodium hypochlorite in CarisolvTM

gel or pepsin in SFC-V coupled to a more controlled abrasive

mechanical action of the mace-tip metal instrument, tended

to leave some residual caries-affected dentine. CarisolvTM gel

left dentine with a mean AF value of 130 whereas SFC-V

resulted in dentine with a mean AF value of 269, implying

clinical under-preparation in certain areas. These findings, interms of clinical operative minimally invasive dentistry, are

acceptable and arguably more desirable if ultimately, a sealed

adhesive restoration can be placed.

The scanning electron microscopy analysis of the exca-

vated dentine surfaces using resin replicas is a tried andtested

method, permitting accurate subjective analysis of surface

topographical features.17 The findings from this study indi-

cated that the chemical agents in CarisolvTM gel had the ability

to alter significantlythe smear layer created by the mechanical

action of the abrading instrumentation used. SFC-V Biosolv

subjectively did not appear to be as efficient in smear layer

removal. This might be due to the rapid neutralisation of the

acidic pH on the dentine surface, so reducing the efficacy ofthe pepsin action on the organic component of the smear

layer.

These findings led to the conclusion that each caries

removal technique left dentine surfaces that were histologi-

cally different from one another, thus rejecting the first

proposed null hypothesis.

Using three different caries excavation techniques (Car-

isolvTM gel, SFC-V and hand excavation) has no effect on

adhesive bond strengths to residual carious dentine, when

comparing total-etch and self-etching dentine bonding sys-

tems.

Analysis ofFigs. 6 and7 revealed that using different caries

excavation techniques did have an effect on the microtensile

bond strength (mTBS) of adhesives to dentine. This finding was

in agreement with Sonoda et al.26 and Tosun et al.30 but

conflicted with Cehreli et al.23 Moreover, the two types of

adhesives used in this study reacted differently with the

varying histological types of dentine left after caries removal,

in agreement with Tosun et al.30 and Koyuturk et al.22 but in

conflict with the findings of Nakornchai et al.21

The CFOME AF measurements indicated that hand excava-tion tended towards over-preparation with more histologi-

cally sound dentine at the cavity walls. SEM examination

showed that hand excavation produced smearing and smear

plugs in the tubular orifices. Interestingly, Scotchbond 1XT

(two-step, etch-and-rinse adhesive) produced the highest

mTBS to this dentine compared to mTBS to residual carious

dentine remaining after the chemo-mechanical techniques.

However, the Filtek Silorane bond (two-step, self-etching

primer adhesive) samples exhibited the lowest mTBS to the

sound dentine. Although the dentine that is left after caries

removal using hand excavation has similar hardness to that of

normal sound dentine, there are ultra-structural differences.

It is known that as caries progresses, translucent dentine(sclerotic dentine) is deposited within the tubules at the

advancing front of the lesion, that can lead to their complete

obliteration. This fact, in conjunction with the formation of a

smear layer that has a higher organic content, due to the

increased bacterial load, may interfere with ability of the

relatively mild self-etching Silorane adhesive to penetrate this

smear layer and demineralise the underlying dentine thus

leading to a reduced mTBS compared to that of the etch-and-

rinse Scotchbond 1XT adhesive. Studies that used caries

excavation techniques that tended to over-prepare cavities

and form a thick smear layer (for example, round steel burs,

lasers and abrasive silicon paper sample preparation techni-

ques) all reachedsimilar observations,that the etch-and-rinseadhesives demonstrated stronger bond strengths to caries-

affected dentine than the self-etch adhesives20,29,31. It was

demonstrated that the use of conventional hand excavation

appears to weaken the bond strength of self-etch adhesives to

the remaining dentine and they attributed this finding to the

presence of an infected smear layer.26

CFOME indicated that CarisolvTM gel excavation was more

selective than hand excavation leaving residual caries-affect-

ed dentine which is partially demineralised; the intertubular

dentine exhibits a high degree of porosity and some of the

dentinal tubules are filled by more acid-resistant mineral

crystals (whitlockite).32 SEM also indicated that CarisolvTM gel

produced a roughened surface with minimal smear layercoverage of the dentine surface leaving mainly open tubular

orifices. The self-etching Silorane adhesive established a

stronger bond to this dentine than the etch-and-rinse

Scotchbond 1XT adhesive. It was found that self-etch

adhesives penetrate deeper and form a thicker and smoother

hybrid layer when CarisolvTM gel was used to remove caries.23

The authors assumed that the removal of the smear layer by

the action of CarisolvTM gel allowed the self-etch adhesive to

penetrate deeper than when it was applied to a smear layer-

covered dentine. Sonoda et al. also confirmed that self-etch

adhesives exhibited improved bond strengths to dentine

remaining after CarisolvTM excavation.26 In the case of etch-

and-rinse Scotchbond 1XT adhesive, it was assumed that the



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removal of the smear layer by the action of CarisolvTM gel

permitted the phosphoric acid etch to demineralise dentine to

a deeper depth so exposing a thicker collagen layer. This

thicker collagen layer may have prevented full penetration of

the adhesive leaving an inner layer of collagen poorly

embedded with resin. In addition, the presence of acid-

resistant crystals in the dentinal tubules may have interfered

with resin tag formation.33 All of these factors may beattributable to the lower bond strength values obtained when

bonding Scotchbond 1XT adhesive to dentine remaining after

caries removal using CarisolvTM gel.

Using enzymes to enhance hand excavation is a relatively

new concept in caries research.4,15 SFC-V Biosolv is an

experimental gel that unlike CarisolvTM does not contain

NaOCl but instead it contains pepsin as its active ingredient.

Furthermore, CarisolvTM is highly alkaline (pH 12) whilst SFC-

V is acidic (pH 3) in nature. The results of this study showed

that the more acidic SFC-V Biosolv chemo-mechanical

excavation left behind a softer and rough dentine surface

topography with varying levelsof smear layer, differentto that

observed with the CarisolvTM samples. Both these factorscontributed to the mTBS values indicating that the type of

dentine remaining after SFC-V Biosolv excavation was

compatible with both etch-and-rinse Scotchbond 1XT and

self-etching primer Silorane adhesives.

This investigation did not endeavour to assess the longer

term durability of adhesive bonds to carious dentine and there

is evidence that these interfaces may undergo more rapid

long-term hydrolysis, phase separation of the hydrophilic and

hydrophobic components and/or breakdown due to the action

of dentine metallo-matrix proteinases (MMPs). This aspect of

adhesive bonding to dentine requires further investigation. It

is essential that, in a clinical situation, optimal enamel

margins are maintained to obtain the best peripheral sealachievable. However, in this study, the results of microtensile

bond strength testing meant that this null hypothesiswas also

rejected.

Using three different caries excavation techniques (Car-

isolvTM gel, SFC-V and hand excavation) has no effect on the

failure mode and loci of failure when bonding to the residual

carious dentine, comparing total-etch and self-etching den-

tine bonding systems.

The adhesiverestorative interface is comprised of five

aspects from the dentine side across to the composite,

through the adhesive (bond) layersee Table 2. This study

used confocal microscopy to analyse the external surfaces of

the stick samples, permitting a more detailed evaluation ofthefailuretypeand loci from mTBSstudies. Most ofthesetend

to analyse the two plane-ended fracture surfaces end-on,

often with SEM. The interpretation of the surface topography

and structure can be difficult and open to interpretation.

Using the present technology, a more detailed picture of the

variability in the fracture mode and position was formed. It

was apparent from the data that samples in all groups

suffered similar proportions of cohesive failure in the

composite aspect of the restorative interface. The self-etch

Silorane bond samples did not suffer any cohesive failures in

dentine, even within the chemo-mechanical caries excava-

tiongroupswhichleftresidual,softercaries-affecteddentine.

This was possibly due to the deeper infiltration of the self-

etching primer and adhesive into the affected dentine with a

reduced smear layer so potentially reinforcing the tissue

against cohesive failure aswell asthe fact that FiltekSilorane,

due to its ring-opening siloxaneoxirane chemistry, exhibits

very low polymerisation shrinkage (0.9%). This would gen-

erate less shrinkage stress at the adhesive interface, so

reducing the forces tending to pull the structurally weaker

affected dentine apart. The Silorane group did suffer from aproportion of type 4 failures (between adhesive and compo-

site) potentially indicating a less robust interface in some

samples that those created by the etch-and-rinse DBA and

resin composite combination and this finding might require

further investigation. From both adhesive groups, etch-and-

rinse and self-etch, it was apparent that broadly similar

proportions of failure type and locations were observed

across the three excavation sub-groups.

Therefore,again, this null hypothesiswas rejected from the

presented data.

5. Conclusions

The three caries hand-excavation techniques used in this

study retained varying histological qualities of sound

through to affected dentine at the cavity walls post-

excavation (hand excavation > CarisolvTM gel > SFC-V Bio-

solv, respectively) and the CFOME instrument was useful in

analysing this tissue via its AF signal, in situ objectively.

This fibre-optic technology may be developed for future

clinical use. The microtensile bond strengths and failure

modes of the two types of adhesive (etch-and-rinse vs. self-

etch) showed variations in their ability to adhere to the

differing dentine structure and a range of failure types

throughout the adhesive interface. The low-shrink Siloraneadhesive/composite system appeared to exert less stress on

the dentineadhesive interface.

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