d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 801809

Available online at www.sciencedirect.com

jo u rn al hom epa ge : www.int l .e lsev ierhea l th .com/ journa ls /dema

Effect of layering methods, composite type, and owableliner on the polymerization shrinkage stress of light curedcomp

Youngcha Departmenb DepartmenUniversity, P

a r t i c

Article histor

Received 21

Received in

14 Decembe

Accepted 16

Keywords:

Polymerizat

Silorane com

Flowable co

Incrementa

Cuspal dee

CorresponUniversity, 2

E-mail a0109-5641/$http://dx.doosites

ul Kwona, Jack Ferracaneb, In-Bog Leea,

t of Conservative Dentistry and Dental Research Institute, School of Dentistry, Seoul National University, Seoul, South Koreat of Restorative Dentistry, Division of Biomaterials and Biomechanics, School of Dentistry, Oregon Health & Scienceortland, OR, USA

l e i n f o

y:

September 2011

revised form

r 2011

April 2012

ion shrinkage stress

posite

mposite lining

l lling

ction

a b s t r a c t

Objectives. The aim of this study was to investigate the effect of layering methods, owable

composite liner and use of low shrinkage silorane-based composite on the polymerization

shrinkage stress of light cured composites.

Methods. Aluminum blocks were used to prepare MOD cavities and divided into four groups.

A universal hybrid methacrylate-based composite (Z250), a owable composite (Z350 ow-

able), and a silorane-based composite (P90) were used to ll the cavities. Cavities were

restored using four different lling protocols. Group 1 was lled in bulk with Z250, group 2

was restored by an increment technique with the same composite, group 3 by an increment

technique with Z250 and a Z350 owable lining, and group 4 was restored by an increment

technique with P90. The axial shrinkage strain and exural modulus of the three composites

were determined, and cuspal deection of each group was measured with LVDT probes and

compared among groups using ANOVA and Tukeys post hoc test ( = 0.05).

Results. The axial shrinkage strains of P90, Z250, and Z350 owable were 1.09 (0.11), 2.29

(0.06), and 4.12 (0.08)%, respectively. The exural modulus of P90 was 10.1 (0.9), Z250 was

13.6 (2.0), and that of Z350 owable was 7.6 (0.9) GPa. The cuspal deections at 33 min

in groups 14 were 18.2 (1.54), 14.5 (0.47), 16.2 (1.10), and 6.6 (0.44) m, respectively. The

incremental lling technique yielded signicantly lower cuspal deection than the bulk

lling technique. Flowable composite lining under universal composite (Z250) layering

showed higher cuspal deection than that without owable composite lining. Silorane-

based (P90) composite exhibited lower cuspal deection than metacrylate based (Z250)

composite.

Signicance. Cuspal deection resulting from polymerization shrinkage stress may be

reduced by an incremental lling technique and by the use of low shrinking compos-

ite to obtain optimal clinical outcomes. Flowable composite lining under conventional

composite layering did not reduce polymerization shrinkage stress as assessed by cuspal

deection.

2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

ding author at: Department of Conservative Dentistry and Dental Research Institute, School of Dentistry, Seoul National8 Daehak-ro 5-gil, Jongno-gu, Seoul 110-749, South Korea. Tel.: +82 2 2072 3953; fax: +82 2 2072 3859.ddress: inboglee@snu.ac.kr (I.-B. Lee).

see front matter 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.i.org/10.1016/j.dental.2012.04.028

802 d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 801809

1. Introduction

Compositeday dental systems, thmore emphsion resistasince theiexpanded However, tstress still materials, assess and

Polymerbetween a tcomposite bond failurtation and post operatfailure requ

Efforts hand to devtion shrinkller loadincan be harresin matrby decreasiing molecualso has itweight mopoor handling strengtwith compshrink concomposite oxirane has

Clinical stress of cto decreasarea/non-bdelay cure increasing the use of owable co

Conictcacy of incelement acuspal exlling of ccuspal desiderably rcompared been reporin higher reto bulk llicant differeincrementathe difculof resin o

methods, and to the difculty in standardizing tested speci-mens [13,14].

asureting ted tigni

stantics ted asteaionsremwer tcant l lliabl

ing lity af polsite igniinter

cone usadheraneage site nive

rinkasitesst seakahe erizah proeffechemimea

curiOD gatesite site s.

Ma

Cu

VDT SolaYZ taree . Cueasu(PCI-cqui restoration has become an essential part of every-practice with the improvement in dental adhesivee increase in patients demand for esthetics andasis on preservation of tooth structure. The abra-nce of dental composites has continued to improver introduction as dental restoratives, enablinguse in posterior restorations with good longevity.he polymerization shrinkage and its associatedremains a major drawback of dental compositeand numerous studies have been performed to

reduce the polymerization shrinkage stress [18].ization shrinkage causes stress at the interfaceooth and a restoration as the elastic modulus of theincreases during curing. This stress manifests ase, cuspal exure, enamel microcracking, pulpal irri-secondary caries due to bacterial inltration, andive sensitivity, which in turn can lead to restorationiring re-restoration [2,4,7,9].ave been made to increase inorganic ller loadingelop a new resin matrix to reduce polymeriza-age of composites. However, increasing inorganicg is limited to a level that the surface of llers

moniously combined physico-chemically with theix. Polymerization shrinkage can also be reducedng reactive sites per unit volume through increas-lar weight per reactive groups. But this strategys limitations because the use of high molecularnomers produces increased viscosity, resulting ining characteristics [2,4,5], as well potentially reduc-h [6]. Therefore, attempts to develop compositesletely new resin matrices that do not shrink orsiderably less, have been ongoing, and recently awith silorane resin matrix containing siloxane and

been introduced [10,11].strategies suggested to minimize shrinkage

omposites include incremental lling techniquee C-factor (conguration factor = bonded surfaceonded surface area) [1214], soft-cure or pulse-methods to slow polymerization by more graduallylight intensity from the curing units [15,16], andlow-modulus intermediate liner material such asmposites to absorb shrinkage stress [1719].ing results have been reported regarding the ef-remental lling technique. Studies using the nitenalysis method [20,21], and a study measuringure in premolar teeth [22] reported incrementalomposites produces higher shrinkage stress andection. In contrast, other studies have shown con-educed cuspal deection with incremental llingto the bulk lling technique [13,14]. It has alsoted that the incremental lling technique resultedsindentin micro-tensile bond strength comparedng in large cavities whereas there was no signi-nce in small cavities [23,24]. The controversy overl and bulk lling techniques can be ascribed toty in exactly simulating the transitional changesw during polymerization, to the different testing

Meevaluaextracduce slack ofacterisfabricasion indeectthe incably losignimenta

Flowabsorbelastiction ocompoto be sas an [27]. Inthat that the

Siloshrinkcompoand a uthe shcompo

Momicroluate tpolymof teetstress histocstudy positewith Minvesticompocompoposite

2.

2.1.

Two L(AX-1,two Xwith th(Fig. 1)the mboard data ament of cuspal deection is a useful way forpolymerization shrinkage stress, but the use ofeeth for cuspal deection measurement can pro-cant discrepancies among specimens due to thedardizing the anatomical and histochemical char-of each individual tooth [13,2527]. Park et al. [14]luminum blocks with identical shape and dimen-d of using extracted teeth and measured cuspal

of the aluminum blocks. The cuspal deection inental lling technique was shown to be consider-han for the bulk lling technique, and there was nodifference between horizontal and oblique incre-ng techniques.e composite has been recommended as a stress-iner or base owing to its relatively low modulus ofnd greater ability to deform to contribute to reduc-ymerization shrinkage stress from the overlyingrestorative [24]. Cuspal deection has been showncantly lower with the use of a owable compositemediate layer than without a owable compositetrast, a study using a photoelastic model reportede of owable composite increased shrinkage stresssive interface [28].-based composite shows lower polymerizationcompared to conventional methacrylate-based[29], however studies using a stressstrain analyzerrsal testing machine reported that simply reducingge does not ensure reduced stress development in

[30,31].tudies have used indirect methods, such asge and micro-tensile bond strength tests, to eval-effects of various clinical methods to reducetion shrinkage stress. Measuring cuspal deectionvides a more direct representation of contractionts, but is made difcult by the morphological andcal differences of natural tooth substrates. Thissured cuspal deection in real time during com-ng, using standardized, uniform aluminum blockscavity preparations. The aim of this study was to

the effects of layering methods, the use of owableliner, or the use of low shrinkage silorane-basedon polymerization shrinkage stress effects of com-

terials and methods

spal deection measurement instrument

(linear variable differential transformer) probesrtron Metrology, West Sussex, UK) were set onbles (Micro Motion Technology, Bucheon, Korea)attached micrometers (Mitutoyo, Kawasaki, Japan)spal deection was detected by LVDT probes andred value was collected using a data acquisition6024, National Instruments, Austin, TX, USA) andsition and analysis software (Labview, National

d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 801809 803

Fig. 1 Schematic diagram of the instrument formeasurement of cuspal deection.

Instruments). The sensitivity of the LVDT probes exceeded0.1 m in the range of 1 mm.

2.2. Specimen preparation

Twenty four aluminum blocks (10 mm 8 mm 30 mm) witha MOD cavity [6 (W) mm 8 (L) mm 4 (D) mm] were fabri-cated using a milling machine, creating two remaining cusps[2 (T) mm 8 (L) mm 4 (H) mm] (Fig. 2a). The inside of the cav-ity was air-abraded with 50 m Al2O3 powder and thoroughlyrinsed with water using a three-way syringe.

Composites used for lling the MOD cavities were amethacrylate-based universal hybrid composite (Z250: 3 MESPE, St. Paul, MN, USA), a owable composite (Z350 owable:

Fig. 2 (a) for a MOD two notche

3 M ESPE), and a silorane-based composite (P90: 3 M ESPE)(Table 1). Scotchbond multipurpose adhesive (3 M ESPE) wasapplied prio(Z250 and Zprior to silthe manufusing a LEintensity wmeter, Mollight guide approximacap with twand placedfrom beingto positiontips (Fig. 2lubricated from beingon the sidesufcient cof composi

2.3. Comdeection

The requireculated fromthe cavity, aensured byblocks werecomposites

Group 1cured from

tal s0 s).up 2l layeand e. Thhe lted sirradccluposigona0 s).up 3the dis(total 8

Gromenta1 mm surfacered. Tirradiamum from oof comthe dia(total 8

GroDimensions (mm) of aluminum block machinedcavity, (b) aluminum block in the acrylic cap withs for probe positioning.

layer was ness, followincrement 80 s).

Group 4ite): P90 wawas light cu

In the inposite was erepresentinlling grouwere lled deection r to placement of methacrylate-based composites350 owable) and P90 system adhesive was appliedorane-based composite (P90) as recommended byacturer. The adhesive was light cured for 10 sD light curing unit (S10: 3 M ESPE), and the lightas measured as 1160 mW/cm2 (EPM 1000 powerectron Detector Inc., Oregon, USA). The radius ofwas 10 mm, and the light guide was positioned attely 2 mm from the irradiated surface. An acrylico notches on the cuspal wall sides was fabricated

on the aluminum blocks to prevent the composite pushed out of the cavity during layering, and

the LVDT probes precisely 1 mm from the cuspb). The internal surface of the acrylic cap waswith petroleum jelly to prevent the composite

adhered and to ensure free surfaces of compositess facing the acrylic cap. The acrylic cap also hadompliance to allow the expansion or contractiontes and aluminum molds.

posite lling and measurement of cuspal

d amount of composite to ll the cavity was cal- the density of the composites and the volume of

nd equal amount of composites for each cavity was weighing the material before use. The aluminum

randomly divided into four groups and lled with by one of following protocols (Fig. 3).

(bulk lling): Z250 was placed in bulk and light the upper surface for 20 s, the mesial side for 20 s,ide for 20 s, and the upper surface for 20 s again

(incremental lling): Z250 was placed in four incre-rs. The thickness of rst horizontal increment wasit was irradiated at a right angle from occlusale second and third increments were obliquely lay-ight guide was slightly tilted perpendicular to theurfaces of second and third oblique layers for opti-iation. The fourth horizontal layer was irradiatedsal direction. Therefore, the maximum thicknesste layer for light curing was less than 2.5 mm atl direction. Each increment was light cured for 20 s

(incremental lling with owable liner): The rstlled with Z350 owable composite in 1 mm thick-ed by three incremental layers with Z250. Each

was light cured for 20 s as done in group 2 (total

(incremental lling with silorane-based compos-s placed in four incremental layers. Each incrementred for 20 s as done in group 2 (total 80 s).

cremental placement groups (groups 24), the com-qually divided into four portions with each portiong a single increment. The composite for the bulkp and the rst layers of incremental lling groupsbefore installing the aluminum block on the cuspalmeasurement instrument. After setting the block

804 d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 801809

Table 1 Composites used in this study.

Composite Lot no. Resin matrix Filler (wt%) Manufacturer

Filtek Z250Universalhybrid

8LXJ Bis-GMA, Bis-EMA, TEGDMA,UDMA

0.013.5 m Zr/silica particles (82 wt%) 3 M ESPE St. Paul, MN, USA

Filtek Z350Flowable

7FX Bis-GMA, Bis-EMA, TEGDMA 520 nm Zr/silicananoparticles + 0.61.4 m nano-clusters(65 wt%)

3 M ESPE

Filtek P90Silorane

N276998 Silorane 0.013.5 m quartz particles, yttriumuoride (76 wt%)

3 M ESPE

onto the metal vise and positioning the two LVDT probes onthe cusp tips, light curing and subsequent layering were per-formed.

Measurement of cuspal deection was initiated 30 s priorto light curing to obtain a base line and continued up to 2000 sat a rate of 2 data points/s. The amounts of cuspal displace-ment measured from both cusps were added to produce totaldeection. Six measurements were performed for each groupat temperature of 25 0.5 C. The data was analyzed by ANOVAand Tukeys post hoc test ( = 0.05).

2.4. Measurement of the axial shrinkage strain andexural modulus of composites

In order to investigate the effect of polymerization shrinkageand elastic modulus of the composites on the cuspal deec-tion, the axial shrinkage strain and exural modulus of thecomposites were measured using a modied bonded discmethod and a universal testing machine, respectively [32,33](Fig. 4). To measure axial strain, a xed amount of compositewas pressed between a slide glass and a exible cover glass

Fig. 3 (a) lling withUn-bondedFour lling groups and dimensions (mm) of increments. Group 1 Z250, group 3: Incremental lling with Z250 and Z350 owable

free surface area in bulk lling group and in each layer of increm: Bulk lling with Z250, group 2: Incrementalliner, group 4: Incremental lling with P90. (b)ental lling group.

d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 801809 805

Fig. 4 (a) measuringmethod. (disc methodiameter o

(Marienfeldeter as a spthickness aa LVDT proset to zero. ing light wLVDT was s(PCI-6024, Nfor 10 min t

Bar typepared by pl2 mm 2 mtions for 4024 h. The wsured, andpoint exusal testing the rate of bases = 20 msured. The the equatio

E = L3P

4WT3D

where E is span (m), Pthe specimcenter of thcomposite.

2.5. Mealuminum

Weights of a point 1 mdisplaceme

Schsp co

. Theispla

Re

Cu

entative cuspal deection curves vs. time are shown 6ad. Cuspal deection increased rapidly with theing of light curing and most of the cusp displacementSchematic diagram of the axial shrinkage instrument using modied bonded discb) Specimen geometry in the modied bondedd, h: thickness of disc-shaped composite, d:f composite.

, Germany) using a metal wire with 0.5 mm diam-acer, producing a disc-shaped specimen 0.5 mm innd 6.0 mm in diameter (aspect ratio = 12). The tip ofbe was placed on the center of the cover glass andA base line was obtained for 20 s, and then the cur-as irradiated for 40 s. The output voltage from thetored on a computer using a data acquisition deviceational instruments) at a rate of 10 data points/s

o determine the axial shrinkage of the composites. specimens for exural modulus tests were pre-acing the composites into stainless steel mold withm 30 mm space, and light cured in three por-

s each, and stored in distilled water at 37 C foridth and thickness of the specimens were mea-

exural modulus was obtained by performing 3

Fig. 5 the cu

(Fig. 5)loadd

3.

3.1.

Represin Fig.beginnral test. Specimens were installed on a univer-machine (4465, Instron, USA), load was applied at0.5 mm/min (distance between the two supportingm), and the loaddisplacement curve was mea-

exural modulus of elasticity was calculated fromn:

,

the exural elastic modulus (Pa), L is the support is the load (N), W is the specimen width (m), T isen thickness (m), and D is the displacement at thee beam (m). Five specimens were tested for each

asurement of the compliance of the cusp ofblock

15.016.0 kg at an interval of 200 g were applied atm from the cusp tip of the aluminum block andnt of the cusp was measured using a LVDT probe

occurred wthe bulk lltion occurrIn the incrdeection i

The me18.2 (1.54), tively, at 20cuspal decantly loweincrementacuspal deowable linlling grouicantly lowmethacryla

3.2. Axcomposites

The axial (Z350 owaematic diagram of the instrument for measuringmpliance of aluminum block.

cusp compliance was obtained from the measuredcement relationship (n = 5).

sults

spal deection during composite llingithin 500 s, and gradually increased thereafter. Ining group (group 1), 50% of the total cuspal deec-ed within 40 s after the initiation of light curing.emental lling groups (group 24), the amount ofncreased in a stepwise manner.an values of cuspal deection in groups 14 were14.5 (0.47), 16.2 (1.10), and 6.6 (0.44) m, respec-00 s after initiation of measurement (Fig. 7). The

ection in the incremental lling group was signi-r than that in the bulk lling group (P < 0.001). Thel lling group with owable liner showed higherection than the incremental lling group withouter (P = 0.035). The deection of the incremental

p with silorane-based composite (P90) was signif-er than that in the incremental lling group withte-based composite (Z250) (P < 0.001).

ial shrinkage strain and exural modulus of

shrinkage strains of composites were 4.12%ble), 2.29% (Z250), and 1.09% (P90). The exural

806 d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 801809

Fig. 6 Rep . (a) Incrementalling withexpansioncomposite

modulus ofollowed by(7.6 GPa) (Ta

3.3. Com

The complthe cusp tip

0

5

10

15

20

25

G

Fle

xu

re (

um

)

Fig. 7 resentative curves of cuspal deection as a function of time

l lling with Z250, (c) group 3: Incremental lling with Z250 and

P90. The asterisks (*) indicate the downward drops in cuspal de at the initiation of each light curing. The arrows indicate the spilayering into the cavity.

f composite was the highest in Z250 (13.6 GPa), P90 (10.1 GPa), and the lowest in Z350 owableble 2).

pliance of the cusp of aluminum block

iance of the cusp of aluminum block at 1 mm from was 0.27 m/N.

rou p 1 Group 2 Group 3 Group 4

Filli ng Me thod

a

b

c

d

Cuspal deection for each group at 2000 s.

4. Di

Cuspal defoof composvaluable mshrinkage sdirectly [9,shown to methods ancuspal detooth substfeatures of defects [13this study,

Table 2 composit

Composit

Z250 Z350 owaP90

Numbers iGroup 1: Bulk lling with Z250, (b) group 2:

Z350 owable liner, (d) group 4: Incrementalection curves caused by the effect of thermalkes caused by mechanical noises during

scussion

rmation resulting from polymerization shrinkageites is of clinical importance, and it can be aethod of assessing the effects of polymerizationtress where stress in a tooth cannot be measured22]. The amount of cuspal deformation has beenrange from 5 to 25 m and varies with testingd experimental conditions [13,14,22,25,27,34]. The

ection can be inuenced by physical properties ofrate itself, such as elastic modulus [35], anatomicalthe tooth including cusp size and shape, structural], and the hydration state of the teeth [25,26]. Inprecisely fabricated aluminum blocks were used

Axial shrinkage strain and exural modulus ofes.

e Axial shrinkagestrain (%)

Flexural modulus(GPa)

2.29 (0.06)b 13.6 (2.0)a

ble 4.12 (0.08)a 7.6 (0.9)c

1.09 (0.11)c 10.1 (0.9)b

n parenthesis are standard deviations.

d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 801809 807

to minimize these variables. In addition, aluminum maysimulate the whole tooth well because its elastic modulus of68.5 GPa is (18.3 GPa) [3

The alumMOD cavitidimensionsamount ofcisely weigheach layer. containers ambient lig

Deectioobserved oan aluminument with ccuspal deat the interformed in between cobonding wa

The custhe light cthermal expolymerizarary expanslight curing

In the bcould be ocuring (Fig.thermal exlight curingmerizationlling grousecond, thithe cuspal dvals for eacallowed thecaused by tmental llialso increaas each layavailable foand resulteas layering

Cuspal dnicantly logroup, whi[13,14]. Incrface areas layer to havbonded sutime and fre-arrangemmerizationunbonded incrementain the bulktical bondein the free

amount of cuspal deection summed from all increments inthe incremental lling group compared with that of the bulk

grourane

de50). Tic rineasu

whi40.9g cut of f thing tmajoianceprodsite the c

cavage peecoug

silohosetionringore, f silohe cu

were of btionownw

movg, nwithard

as she P9tencptathavettacDT pDT pons, fter

signgatiDT

signard ese tetwee lay

use polyus [4at thbetween that of the enamel (84.1 GPa) and dentin6,37].inum blocks used in this study had identical-sized

es to minimize the discrepancies in remaining cusp, and to simulate the compliance of real tooth. The

the composite used to ll each cavity was pre-ed prior to use to ensure equal amounts placed for

Prepared composites were stored in light protecteduntil placement since sensitivity of composites toht can affect the results.n of the cusps of the aluminum mold can be

nly when there is strong bond at the interface ofm mold and a composite restoration. Each incre-omposite showed a clear and consistent pattern ofection which suggests sufcient bond establishedface. In addition, acoustic emission tests were per-a supplementary experiment to assure adhesionmposite and the aluminum molds, and no de-s observed.pal deection curves showed slight drops whenuring started, which could be interpreted as thepansion effect by the heat of curing light and oftion reaction of composite. Thereafter, this tempo-ion of composites caused by the thermal effect of

was offset by the polymerization shrinkage.ulk lling group 1, the thermal expansion effectbserved only at the beginning of the nal light

6a). The possible explanation would be that thepansion by the rst, second and third consecutive

have been masked by the rapidly developing poly- shrinkage. On the other hand, in the incrementalps 24, each thermal expansion effect by the rst,rd, and fourth light curing was clearly observed ineection curves (Fig. 6bd). There were time inter-h composite layering between light curing, which

composite to cool down before thermal expansionhe beginning of the each light curing. As the incre-ng proceeded, the magnitude of the thermal effectsed. Since the total volume of composite increaseder was added, the more volume of composite wasr thermal expansion by the heat of the curing light,d in more prominent drop in the deection curves

proceeded.eection in the incremental lling group was sig-wer (20.3% reduction) than that in the bulk llingch corroborates the results of previous studiesemental layering can present additional free sur-between layers, allowing the composite of eache compensatory ow during curing with the samerface area as in bulk lling. If there are enoughree surface area at the boundary layer for theent of monomers in polymer network, the poly-

stress can be reduced [3,12,17]. The total sum offree surface area (215 mm2) by each layer in thel lling group was much larger than that (96 mm2)

lling group while both groups having the iden-d surface area (112 mm2) (Fig. 3b). This differencesurface area can explain signicantly lower total

lling Silo

cuspalite (Z2cationThe m1.09%,ies, 0.9causinamounulus oAccordis the complto the compostudy, a MODshrinkcusp d

Althtion ofthan tadaptaand cuTherefcacy o

In tspikessibilityrestorarary dby thelayeringraph downwshownues. T(consisite adamight mold atwo LVone LVdirectiately aoutputwas netwo LVoutputdownwthat thment bobliqu

Thereducemoduling thp (Fig. 3b).-based composite (P90) showed signicantly lessection than that of methacrylate-based compos-he silorane-based composite is polymerized withg opening mechanism providing low shrinkage.red axial shrinkage of P90 in this study wasch corresponds with the results of other stud-8 vol% [10,11,38]. Polymerization shrinkage stressspal deection is primarily dependent on thepolymerization shrinkage strain, the elastic mod-e composite, and the compliance of the cusps.o the study by Min et al. [33], the shrinkage strainr factor determining stress when the instrument

is high, whereas shrinkage stress is proportionaluct of shrinkage strain and elastic modulus of thewhen the instrument compliance is low. In ourompliance of the cusp of the aluminum block withity was high (0.27 m/N), therefore, P90 with low-roduced less shrinkage stress resulting in lowesttion.h the polymerization shrinkage and cusp deec-rane-based composite (P90) is signicantly lower

of methacrylate-based composites, the issues of of silorane-based composite to the cavity wall

limitations in deep cavities have been raised [39].further study is needed to validate the clinical ef-rane-based composites (P90).spal deection curve of P90 (Fig. 6d), the downward

shown. These could be the concern about the pos-ond failure at the interface between a composite

and an aluminum mold. However, these tempo-ard spikes were the mechanical noises causedement of the aluminum mold during compositeot by de-bonding. We examined thoroughly the

an expanded x-axis, and there were no permanentsteps showing bond failure. The mechanical noisespikes returned immediately to their previous val-0 silorane composite showed very high viscosityy), which required more packing force for compos-ion into the cavity walls of aluminum mold, which

caused the temporary movement of the aluminumhed to the LVDT sensors. As a consequence, therobes abruptly shifted to one side, which causedrobe to move inward and the other probe outwardand returned to their previous position immedi-composite packing. The changes of the two LVDTals were opposite (one was positive and the otherve). If there was de-bonding, the polarities of thesignal changes should be the same both LVDTals should be negative, resulting in permanentsteps in the cuspal deection curve. We conrmedemporary spikes occurred during composite place-en light curing, especially during second and third

ering of P90. of owable composites as a liner is believed tomerization shrinkage stress owing to its low elastic0,41]. However, there are conicting studies report-e owable composite liners do not reduce stress

808 d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 801809

and microleakage [4244]. In our study, the incremental ll-ing group with a owable composite liner (group 3) showedhigher cus(group 2) (Pment layerwas consida conventiwas maint(Fig. 6b andhigh shrinkfactor in prthat of thestudy. Lee cavities hashould havto perform blocks withand MOD cance of rem

Theoretshrinkage sshrinkage spolymerizain thicknesment by thecorrespondthe materiathese prodmeasuremthe specim

= t

0

(ESp

where is tmodulus atspecic timdirectly thecomposite the initiatiothe exact staddition to

As the cproperties,the exact locusp at theent. The coblock at 1 1/41/5 of tand measution shrinkestimated atively.

In this stained concuspal dechanging tstrates [45]thickness pHowever, u

modulus, shrinkage values, and varying thickness might pro-duce different results. Resin modied glass ionomer is also

sed e res

in ter our

com

r e n

nhovntracethaaga Rntracologyvidslymestorarracaperieansbnverd cotterm

nda Rmmesin-buvilrinkathetierleyntheonomntbirH. Tostoraeinmntal padottingw-sh09;25ilzermpostorae MRmens

prem07;23rk JK

layeling?h BI.rinkampee N, Frinkith mvidsntracntalilzertermstorapal deection than that without a owable liner = 0.0351). The cuspal deection of the rst incre-ed with a owable composite liner (Z350 owable)erably higher than the rst increment layered withonal hybrid composite (Z250), and the differenceained until 2000 s after initiation of light curing

c). This phenomenon could be explained by theage strain of owable composite, which is a majoroducing stress in a high compliance situation like

MOD cavity within the aluminum block in thiset al. [33,35] suggested that teeth with preparedve some compliance and that the testing systeme compliance comparable to that of a tooth in orderclinically relevant studies. In this study, aluminum

elastic modulus similar to teeth have been usedavities were prepared to simulate similar compli-aining cusps of a tooth.

ical shrinkage stress can be estimated from thetrain and elastic modulus of a composite. Both thetrain and elastic modulus of composites change astion progresses. Therefore, multiplying the changes of a composite specimen at a specic time seg-

elastic modulus of the material at that time would to the shrinkage stress increment at that time ifl behaved in a totally elastic manner. Integrating

ucts from the beginning of light curing to a nalent time would give the total cumulative stress inen and can be expressed as:

ecific Time dSpecific Time Segment)

he polymerization shrinkage stress, E is the elastic a specic time, and d is the shrinkage strain at ae period. However, it is very difcult to determine

exact values of elastic modulus of polymerizingthroughout the entire polymerization process fromn of light curing to the nal curing stage. Therefore,ress values should be measured by experiments in

numerical simulation studies.ompliance is a compound of various mechanical

anatomy, bonding conditions, and will vary withcation where it is determined, the compliance of

level of each incremental layer would be differ-mpliance of the remaining cusp of the aluminummm from the cusp tip was 0.27 m/N, which iseeth with a MOD cavity [35]. From the compliancered cuspal deection, the minimum polymeriza-age forces exerted on the cusp in groups 14 ares approximately 67.3, 53.7, 59.9, and 24.4 N, respec-

tudy, the compliance of aluminum mold was main-stant. It requires further study to compare theections depending on the varying compliance byhe thickness of cuspal wall or using other sub-. The composite lining with Z350 owable in 1 mmroduced higher cuspal deection in this study.

sing owable composite liners with different elastic

often upare thliners add todental

r e f e

[1] Vecom

[2] BrcoBi

[3] Dapore

[4] Feex

[5] StCoan

[6] RJacore

[7] DashEs

[8] BySym

[9] TaWre

[10] Wde

[11] PaSelo20

[12] Fecore

[13] Lediof20

[14] Pabel

[15] SushCo

[16] IliShw

[17] DacoDe

[18] Federeas a liner [28,46], and further investigation to com-in modied glass ionomer with owable compositems of cuspal deection and shrinkage stress wouldunderstanding on the efcacy of liner material inposite restoration.

c e s

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Dental Materials 2008;24:15015. Controlling and understanding the polymerizationge-induced stresses in light-cured composites.ndium 1999;20:S3441.elten K, Trixner K, Hickel R, Kunzelman KH.age behavior of a resin-based composite irradiatedodern curing units. Dental Materials 2005;21:4839.on CL, De Gee AJ. Relaxation of polymerizationtion stresses by ow in dental composites. Journal of

Research 1984;63:1468. AJ, De Gee AJ, Davidson CL. Quantitativeination of stress reduction by ow in compositetions. Dental Materials 1990;6:16771.

d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 801809 809

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[25] Meredistrain aJournal

[26] Sulimaof comJournal

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[28] Oliveiralow-elain com2010;26

[29] Lien Wsiloran2010;26

[30] MarcheCadenamateriMateria

[31] Boaro LA, BragmoduluDental

[32] Lee IB, consist

polymerization shrinkage measurement of light curedcomposites. Dental Materials 2006;22:10719.

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[38] Lee IB, Min SH, Seo DK, Kim SY, Kwon YC. A new method tomeasure the linear polymerization shrinkage of compositesusing a particle tracking method with computer vision.

urnal of Korean Academy of Conservative Dentistry10;35de Aes ahesievailicroled wi01;26omarecteratme A

ass II vitrodenaS, Brntrac09;25aga Rwablress-sociaeira Jders

sts. Johim In-calectio07;23W, Frankenberger R. Inuence of c-factor and layeringue on microtensile bond strength to dentin. Dentalls 2004;20:57985.th N, Sethchell DJ. In vitro measurement of cuspalnd displacement in composite restored teeth.

of Dentistry 1997;25:3317.n A-H, Boyer DB, Lakes RS. Polymerization shrinkageposite resins: comparison with tooth deformation.

of Prosthetic Dentistry 1994;71:712., Fleming GJP, Palin WM, Walmsley AD, Burke FJT.

deection and microleakage in premolar teethd with resin-based composites with and without anediary owable layer. Journal of Dentistry:4829.

LCA, Duarte Jr S, Araujo CA, Abraho A. Effect ofstic modulus liner and base as stress-absorbing layerposite resin restorations. Dental Materials:e15969., Vanderwalle KS. Physical properties of a newe-based restorative system. Dental Materials:33744.si G, Breschi L, Antoniolli F, Lenarda RD, Ferracane J,ro M. Contraction stress of low-shrinkage composite

als assessed with different testing systems. Dentalls 2010;26:94753.C, Goncalves F, Guimares TC, Ferracane JL, Versluisa RR. Polymerization stress, shrinkage and elastics of current low-shrinkage restorative composites.

Materials 2010;26:114450.Cho BH, Son HH, Um CM, Lim BS. The effect ofency, specimen geometry and adhesion on the axial

Jo20

[39] EnDoad

[40] LeMan20

[41] AldeOp

[42] Neclin

[43] CaEDco20

[44] BrostAs

[45] MUnte

[46] Icnose20:1807.B, Munck JD, Mine A, Lambrechts P, Meerbeek BV.

low-shrinking composite induce less stress at theve interface? Dental Materials 2010;26:21522.oj C, Cochran MA, Matis BA, Moore BK, Platt JA.akage of posterior packable resin composites withthout owable liners. Operative Dentistry:3027.i QD, Reinhardt JW, Boyer DB. Effect of liners on cuspion and gap formation in composite restorations.ive Dentistry 2001;26:40611.L, Maxon BB, Pink FE, Aksu MN. Microleakage of

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Effect of layering methods, composite type, and flowable liner on the polymerization shrinkage stress of light cured compo...1 Introduction2 Materials and methods2.1 Cuspal deflection measurement instrument2.2 Specimen preparation2.3 Composite filling and measurement of cuspal deflection2.4 Measurement of the axial shrinkage strain and flexural modulus of composites2.5 Measurement of the compliance of the cusp of aluminum block

3 Results3.1 Cuspal deflection during composite filling3.2 Axial shrinkage strain and flexural modulus of composites3.3 Compliance of the cusp of aluminum block

4 DiscussionReferences