801 809 Effect of Layering Methods, Composite Type, And Flowable Liner on the Polymerization Shri

9
d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 801–809 Available online at www.sciencedirect.com jo u rn al hom epa ge : www.intl.elsevierhealth.com/journals/dema Effect of layering methods, composite type, and flowable liner on the polymerization shrinkage stress of light cured composites Youngchul Kwon a , Jack Ferracane b , In-Bog Lee a,a Department of Conservative Dentistry and Dental Research Institute, School of Dentistry, Seoul National University, Seoul, South Korea b Department of Restorative Dentistry, Division of Biomaterials and Biomechanics, School of Dentistry, Oregon Health & Science University, Portland, OR, USA a r t i c l e i n f o Article history: Received 21 September 2011 Received in revised form 14 December 2011 Accepted 16 April 2012 Keywords: Polymerization shrinkage stress Silorane composite Flowable composite lining Incremental filling Cuspal deflection a b s t r a c t Objectives. The aim of this study was to investigate the effect of layering methods, flowable 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 flowable composite (Z350 flow- able), and a silorane-based composite (P90) were used to fill the cavities. Cavities were restored using four different filling protocols. Group 1 was filled 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 flowable lining, and group 4 was restored by an increment technique with P90. The axial shrinkage strain and flexural modulus of the three composites were determined, and cuspal deflection of each group was measured with LVDT probes and compared among groups using ANOVA and Tukey’s post hoc test (˛ = 0.05). Results. The axial shrinkage strains of P90, Z250, and Z350 flowable were 1.09 (0.11), 2.29 (0.06), and 4.12 (0.08)%, respectively. The flexural modulus of P90 was 10.1 (0.9), Z250 was 13.6 (2.0), and that of Z350 flowable was 7.6 (0.9) GPa. The cuspal deflections at 33 min in groups 1–4 were 18.2 (1.54), 14.5 (0.47), 16.2 (1.10), and 6.6 (0.44) m, respectively. The incremental filling technique yielded significantly lower cuspal deflection than the bulk filling technique. Flowable composite lining under universal composite (Z250) layering showed higher cuspal deflection than that without flowable composite lining. Silorane- based (P90) composite exhibited lower cuspal deflection than metacrylate based (Z250) composite. Significance. Cuspal deflection resulting from polymerization shrinkage stress may be reduced by an incremental filling 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 deflection. © 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. Corresponding author at: Department of Conservative Dentistry and Dental Research Institute, School of Dentistry, Seoul National University, 28 Daehak-ro 5-gil, Jongno-gu, Seoul 110-749, South Korea. Tel.: +82 2 2072 3953; fax: +82 2 2072 3859. E-mail address: [email protected] (I.-B. Lee). 0109-5641/$ see front matter © 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.dental.2012.04.028

description

komposit

Transcript of 801 809 Effect of Layering Methods, Composite Type, And Flowable Liner on the Polymerization Shri

  • 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: [email protected] (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

    en BAM, De Gee AJ, Davidson CL. Polymerizationtion and conversion of light-curing BisGMA-based

    crylate resins. Biomaterials 1993;14:8715.R, Ferracane JL. Alternatives in polymerizationtion stress management. Critical Reviews in Oral

    and Medicine 2004;15:17684.on CL, Feilzer AJ. Polymerization shrinkage andrization shrinkage stress in polymer-basedtives. Journal of Dentistry 1997;25:43540.ne JL. Placing dental compositesa stressfulnce. Operative Dentistry 2008;33(3):24757.ury JW, Trujillo-lemon M, Lu H, Ding X, Lin Y, Ge J.sion-dependent shrinkage and strain in dental resinsmposites. Dental Materials 2005;21:5667.ann S, Dluzhevskaya I, Grosssteinbeck C, Raab WH,. Impact of replacing Bis-GMA and TEGDMA by otherrcially available monomers on the properties ofased composites. Dental Materials 2010;26:3539.lier BS, Aarnts MP, Feilzer AJ. Developments inge control of adhesive restoratives. Journal ofc Dentistry 2000;12:2919.

    TJ, Eick JD, Chen GP, Chappelow CC, Millich F.sis and polymerization of new expanding dentalers. Dental Materials 1992;8:34550.ojn D, Versluis A, Pintado MR, DeLong R, Douglasoth deformation patterns in molars after compositetion. Dental Materials 2004;20:53542.ann W, Thalacker C, Guggenberg R. Siloranes incomposites. Dental Materials 2005;21:6874.giannis D, Kakaboura A, Palaghias G, Eliades G.

    characteristics and cavity adaptation ofrinkage resin composites. Dental Materials:150916.

    AG, De Gee AJ, Davidson CL. Setting stress insite resin in relation to conguration of thetion. Journal of Dental Research 1987;66:16369., Cho BH, Son HH, Um CM, Lee IB. Inuence of cavityion and restoration methods on the cuspal deectionolars in composite restoration. Dental Materials:28895., Chang JH, Ferracane J, Lee IB. How should compositered to reduce shrinkage stress: incremental or bulk

    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

    [19] Sadeghi M, Lynch CD. The effect of owable materials on themicroleakage of class II composite restorations that extendapical to the cemento-enamel junction. Operative Dentistry2009;34(3):30611.

    [20] Versluis A, Douglas WH, Cross M, Sakaguchi RL. Does anincremental lling technique reduce polymerizationshrinkage stresses? Journal of Dental Research1996;75:8718.

    [21] Kuijs RH, Fennis WMM, Kreulen CM, Barink M, VerdonschotN. Does layering minimize shrinkage stresses in compositerestorations? Journal of Dental Research 2003;82:96771.

    [22] Abbas G, Fleming GJP, Harrington E, Shortfall ACC, Burke FJT.Cuspal movement and microleakage in premolar teethrestored with a packable composite cured in bulk or inincrements. Journal of Dentistry 2003;31:43744.

    [23] He Z, Shimada Y, Tagami J. The effects of cavity size andincremental technique on micro-tensile bond strength ofresin composite in class I cavities. Dental Materials2007;23:5338.

    [24] Nikolaenko SA, Lohbauer U, Roggendorf M, Petschelt A,Dasch techniqMateria

    [25] Meredistrain aJournal

    [26] Sulimaof comJournal

    [27] Cara RRCuspalrestoreinterm2007;35

    [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.

    [33] Min SH, Ferracane J, Lee IB. Effect of shrinkage strain,modulus and instrument compliance on polymerizationshrinkage stress of light-cured composites during the initialcuring stage. Dental Materials 2010;26:102433.

    [34] Jantarat J, Panitvisai P, Palamara JEA, Messer HH.Comparison of methods for measuring cuspal deformationin teeth. Journal of Dentistry 2001;29:7582.

    [35] Lee SH, Chang J, Ferracane J, Lee IB. Inuence of instrumentcompliance and specimen thickness on the polymerizationshrinkage stress measurement of light-cured composites.Dental Materials 2007;23:1093100.

    [36] Craig RG. Restorative dental materials. 10th ed. Mosby; 1997.p. 66.

    [37] OBrien WJ. Dental materials and their selection. 3rd ed.Quintessence Publications; 2002. p. 119.

    [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

    packable resin composites lined with owables: an study. Operative Dentistry 2002;27:6005.ro M, Marchesi G, Antoniolli F, Davidson C, Dorgioeschi L. Flowability of composites is no guarantee fortion stress reduction. Dental Materials:64954.R, Hilton TJ, Ferracane JL. Contraction stress ofe composite materials and their efcacy asrelieving layers. Journal of the American Dentaltion 2003;134:7218.BC, Braga RR, Ballester RY, Tanaka CB, Versluis A.tanding contradictory data in contraction stressurnal of Dental Research 2011;90:36570.P, Schmidlin PR, Kieser JA, Swain MV. Restoration ofrious cervical lesions. Part II. Restorative materialn to minimise fracture. Dental Materials:15629.

    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