d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 984992

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jo ur nal ho me pag e: www.int l .e lsev ierhea l th .com/ journa ls /dema

Correlation between polymerization stress andinterfacial integrity of composites restorationsassessed by different in vitro tests

Letcia Cristina Cidreira Boaroa,b,, Nvea Regina Fres-Salgadob,ViniciusAndrea Walter Ga Universidab Universidac Universida

a r t i c

Article histor

Received 16

Received in

10 Decembe

Accepted 21

Keywords:

Polymerizat

Composites

Bond streng

Marginal ga

CorresponBrazil. Tel.:

E-mail ahttp://dx.do0109-5641/ Edwardo Souza Gajewskib, Aline A. Bicalhoc,Dolores Correa M. Valdiviac, Carlos Jos Soaresc,omes Miranda Jniorb, Roberto Ruggiero Bragab

de de Santo Amaro, So Paulo, SP, Brazilde de So Paulo, So Paulo, SP, Brazilde Federal de Uberlndia, Uberlndia, MG, Brazil

l e i n f o

y:

February 2013

revised form

r 2013

May 2014

ion stress

th

p

a b s t r a c t

Objective. to correlate polymerization stress data obtained under two compliance conditions

with those from different interfacial quality tests.

Methods. Six commercial composites were tested (Filtek Z250/3M ESPE, Heliomolar/Ivoclar

Vivadent, Aelite LS Posterior/Bisco, Filtek Supreme/3M ESPE, ELS/Saremco and Venus Dia-

mond/Heraeus Kulzer). Bond strength (BS) was evaluated by push-out test on slices of bovine

dentin (2-mm thick) with tapered cavities. For microleakage (ML) and gap analysis, cylindri-

cal cavities in bovine incisors (4-mm diameter and 1.5-mm height) were restored and epoxy

replicas of the cavo-surface margins were prepared for analysis under scanning electron

microscopy (200). The same specimens were submitted to a microleakage protocol usingAgNO3 as tracer. After sectioned twice perpendicularly, ML was determined under a stereo-

microscope (60). Polymerization stress (PS, n = 5) was determined by the insertion of thecomposite (h = 1.5 mm) between poly(methyl methacrylate), PMMA, or glass rods ( = 4 mm)

attached to a universal testing machine. Data were analyzed using KruskalWallis (ML and

gaps), and ANOVA/Tukey (BS and PS, = 5%). Pearsons correlation test was used to verify

correlations between stress and interfacial quality.

Results. BS varied from 4.7 to 7.9 MPa. Average ML data ranged from 0.34 to 0.89 mm. Maxi-

mum ML varied from 0.61 to 1.34 mm. Gap incidence varied from 13 to 47%. PS ranged from

2.5 to 4.4 MPa in PMMA, and between 2.1 and 8.2 in glass. Statistically signicant correla-

tions were observed between stress and interfacial quality, except between BS and PS in

glass. These correlations were stronger when PMMA was used as bonding substrate.

ding author at: Departamento de Biomateriais e Biologia Oral da FOUSP, Av. Prof. Lineu Prestes, 2227, So Paulo, SP 05508-000,+55 11 3091 7840x224; fax: +55 11 3091 7840x201.ddresses: eticiacidreiraboaro@gmail.com, leticiaboaro@usp.br (L.C.C. Boaro).i.org/10.1016/j.dental.2014.05.011

2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 984992 985

Conclusions. PS data obtained using a high compliance testing system showed a stronger cor-

relation with in vitro interfacial integrity results, compared to data from a low compliance

system.

tal M

1. Int

According tive sensitivcaries are ocomposite interfacial dites polymassociated erate stresslead to deb

Several mechanicathe most cand polymor poly(meuniversal tcontractionduring polyin MPa, byof the rod.commerciatoactivationassociated correlated tfacial integincrease prever, no reformation merizationobserved tstress value

The stuthat stress glass as bosystems coregarding sof the testirelief the sIn the pastlus of elast[11,12,23,24

Even assextrapolatesystem wouity of comlow complivalues, in cconditions,mating thenearly imp

teetnce hat c. In rink

us stor mianceed insideerizacial p fotionty, rend ntesti.

Ma

ethtestee a

t (byLS) aals bD-urdimeMA) i (derinkaed ined 1nd ra

Pus

inct-en. Thhe eas seke Bd ca5 mm 2014 Academy of Den

roduction

to clinical studies, drawbacks such as postopera-ity, marginal discoloration and possibly secondaryften associated with loss of marginal integrity inrestorations [13]. One of the possible causes forebonding is polymerization stress. When compos-

erize conned in a cavity preparation, shrinkagewith the development of modulus of elasticity gen-es in the tooth/restoration interface, which mayonding [4].research groups have focused on developing

l tests to quantify polymerization stress [58]. Inommonly used test, the composite is insertederized between two at surfaces of glass, metalthyl methacrylate), PMMA, rods attached to anesting machine [916]. The load cell records the

force exerted by the composite on the substratemerization and the nominal stress is calculated,

dividing this value by the cross sectional area This method has been widely used to comparel [17] and experimental composites [14,18], pho-

methods [19] and to evaluate several factorswith stress development [16]. Some studies havehe stress values from mechanical tests with inter-rity, noting that microleakage and cuspal deectionoportionally with increasing stress [4,20,21]. How-lationship was found between stress and gap

in porcelain inlays [22]. A study evaluating poly- stress as a function of photoactivation methodshat modulated photoactivation results in lowers, leading to higher bond strengths [19].dies mentioned above have in common the factwas determined in low compliance systems, usingnding substrate for the composite. However, thempliance has great inuence on ranking materialstress magnitude [23,24]. The lower the complianceng system, the lower is its ability to elongate andtress. Consequently, the recorded value is higher.

few years, bonding substrates with lower modu-icity have been used polymerization stress testing].uming that data from mechanical tests cannot bed to the clinic, a question arises regarding whichld be more closely related to the interfacial qual-

posite restorations. It is possible that the use of

amongdifferebeing tsystemtion shprevioilarly fcomplobtain

Conpolyminterfaand gamerizaintegria secoof the values

2.

Six dimwere SupremcontenAelite materihas TCtional (TEGDmodulgel shobtainrecordance a

2.1.

Bovinecemenerationuntil tface wLtd., LaTapereand 3.ance testing systems could overestimate the stressomparison with those found in high compliance

more akin to the behavior of a prepared tooth. Esti- compliance of the tooth in a clinical situation isossible. The stiffness of the dental tissues varies

using cylinThe cav

for 15 s anwater was visibly moiaterials. Published by Elsevier Ltd. All rights reserved.

h and even in the same tooth there is a substantialin stiffness between enamel and dentin. But evenomplex, the tooth cannot be considered as a rigidfact, several studies have shown that polymeriza-age could lead to tooth deformation [25,26]. In audy, several commercial composites ranked sim-icroleakage and stress values obtained in a high

system, but the same did not apply to stress data a low compliance system [23].ring the above, it is important to verify if data fromtion stress tests can be correlated with results fromquality tests, namely, bond strength, microleakagermation. The null hypothesis was that the poly-

stress values shows no correlation to interfacialgardless of the system compliance. Additionally,ull hypothesis was tested, stating the complianceng system did not inuence polymerization stress

terials and methods

acrylate-based commercial composites shade A3d (Table 1). Three of them (Heliomolar, Filteknd Filtek Z250) were chosen based on their ller

volume). The other three (Venus Diamond, ELS andre considered as low shrinkage or low stressy the respective manufacturers. Venus Diamondethane in its composition, in addition to conven-thacrylates, while ELS has no diluent monomer

and Aelite LS has a very high ller content. Elastictermined by three point bending test) and post-ge (determined by the strain-gage method) were

a previous study, and correspond to the values0 min after phtoactivation using the same irradi-diant exposure adopted in the present study [27].

h-out bond strength

isors (n = 15) had their crowns removed at theamel junction with a diamond disc under refrig-e buccal surface was attened with wet sandpapernamel was completely removed. The lingual sur-ctioned using a diamond disc (Isomet 1000, Buehlerluff, IL, USA) to obtain a slice with 2 mm thickness.vities with 2.9-mm diameter on the buccal surface

diameter on the lingual surface were prepared

drical and truncated cone diamond burs.ity walls were etched with 37% phosphoric acidd then rinsed in running water for 15 s. Excessremoved with short air blasts, leaving the surfacest. Two layers of an one-bottle adhesive system

986 d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 984992

Tabl

e

1

Mat

eria

ls

use

d

in

the

pre

sent

study

, ller

conte

nt

in

volu

me,

aver

age

size

of

ller

par

ticle

and

man

ufa

cture

s.

The

dat

a

of

pos

t-ge

l shrinkag

e

and

elas

tic

mod

ulu

s

acco

rdin

g

to

Boa

ro

[28].

Mat

eria

l(a

bbre

viat

ion)

Filler

conte

nt

(vol

.)Ave

rage

size

ofller

par

ticl

esM

anufa

cture

r

Org

anic

mat

rix

Post

-gel

Shrinka

ge

(%)

Elas

tic

Mod

ulu

s(G

Pa)

Hel

iom

olar

(HM

)

46%

0.04

0.2

m

Ivoc

lar

Viv

aden

t,

Schaa

n, L

iech

tenst

ein

BisGM

A, U

DM

A, D

3M

A

0.43

(0.0

2)

3.1

(0.3

)EL

S

(EL)

a50

%

0.07

2.6

m

Sare

mco

, Roh

nac

ker,

Switze

rlan

d

BisGM

A, B

isEM

A

0.35

(0.0

2)

2.0

(0.2

)Fi

ltek

Supre

me

(SU)

57%

75

nm

1.4

m

3M

ESPE

BisGM

A, B

isEM

A, U

DM

A, T

EGDM

A

0.64

(0.0

7)

6.0

(0.7

)Fi

ltek

Z25

0

(FZ)

60%

0.19

3.3

m

3M

ESPE

BisGM

A, B

isEM

A, U

DM

A, T

EGDM

A

0.52

(0.0

4)

5.6

(0.6

)Ven

us

Dia

mon

d

(VD)a

64%

5

nm

20

m

Her

aus

Kulz

er

Gm

bH, H

anau

, Ale

man

ha

TCD-u

reta

no

0.39

(0.0

3)

4.5

(0.3

)Ael

ite

LS

Post

erio

r

(AE)

a74

%

0.06

m

Bisco

, Sch

ambu

rg, I

L,

EUA

BisGM

A, B

isEM

A, T

EGDM

A

0.51

(0.0

4)

9.3

(0.7

)

aCon

sider

ed

by

thei

r

resp

ectv

ily

man

ufa

cter

as

low

-shrinka

ge

com

pos

ites

.

(Single Bond 2, 3M ESPE) were applied and photoactivatedwith a radiant exposure of 12 J/cm2 (400 mW/cm2 30 s VIPJr, Bisco, Smylar tapeAfter insertplaced on ttip was plafrom buccawith a radiaimens werbuccal and discs (Soft-

For thestainless stmachine (In(buccal surstainless sta compresscomposite Values in M(N) by the barea was ctruncated c

Bonded are

where = 3h cavity hig

2.2. Mi

Bovine inci#400 grit sato make suby enamel,diameter aall of themwas the saately after polished wremove comAfter 24 h were sonicsurfaces wlight consiswith epoxyIL, USA). Afmolds, xein a scanniunder 200

Ten speselected fo38 and 48 iperimeter ofree marginInstitute oflength of tmargins, asscale bar ofchaumburg, IL, USA). The tooth was placed on a over a glass slab, with the buccal surface facing up.ing the composite in bulk, a second mylar strip washe buccal surface of the restoration and the curingced in contact therewith, so the light was directedl to lingual surfaces. The composite was light curednt exposure of 18 J/cm2 (570 mW/cm2 32 s). Spec-

e stored for 24 h in distilled water at 37 C. Bothlingual surfaces were slightly ground with nishingLex, 3M ESPE).

push-out test, the specimen was placed on aeel base under the actuator of a universal testingstron 5565, Canton, MA EUA). The smallest radius

face) was placed in contact with a 2.5-mm diametereel tip, connected to the load cell. This tip appliedive force (cross-head speed: 0.5 mm/min) on thesurface until the rupture of the bonded interface.Pa were obtained by dividing the maximum forceonded area of the specimen (in mm2). The bondedalculated by the formula of the lateral area of theone:

a = [ (R + r)]

h2 + (R r)2

.1416; R larger cavity radius, r smaller cavity radius;h.

croleakage and marginal gap analysis

sors (n = 15) had their buccal surfaces attened withndpaper to provide an enamel surface large enoughre the cavity margins were entirely surrounded

and then received cylindrical cavities with 4-mmnd 1.5-mm depth (C-factor: 2.5, volume: 19 mm3),

with enamel margins. The restorative procedureme as described for the push-out test. Immedi-polymerization, the restorations were ground andith silicon carbide sandpaper (grits 6004000) toposite excess and expose the restoration margins.

storage in distilled water at 37 C, the specimensated for cleaning the surface. Then, the restoredere molded using an addition silicone (Express XT,tency, 3M ESPE) and the impressions were poured

resin (Buhler Epothin, Epoxicure Resin, Lake Bluff,ter 9 h at 37 C, the replicas were separated from thed in metal stubs and coated with gold for analysisng electron microscope (LEO, AEG-Zeiss, Germany)

magnication.cimens of each experimental group were randomlyr gap analysis. Each specimen required betweenmages using 200 magnication to scan the entiref the restoration. Examples of debonded and gap-s are shown in Fig. 1. ImageJ software (National

Health, Bethesda, USA) was used to measure thehe debonded segments at the enamel-composite

well as the entire perimeter of the restoration. The the SEM images was used for calibration. The value

d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 984992 987

l gap (left) and without gap (right).

obtained inon the tota

After thmen was caround thefor 2 h in thdevelopingunder uortioned withIsomet, Bularly througtooth substness of thepairs of adage evaluat60 magnifTokyo, Japapus). The d(in mm) upenetrationetration wenamel lay

2.3. Pol

Polymerizaconditions,for the comcompliancesegments wof the surfa(6002000 g3, ATM, Altest light tropposite susandblaste

For the layer of mPolimerizanBrasil), whiPrimer, 3M

bond Multipurpose Plus, bottle 3, 3M ESPE), light-cured radiant exposure of 12 J/cm2 (400 mW/cm2 30 s). Theere attached to a universal testing machine (Instron

Thoose was sitesr foltach

specne to

into valuecesnd muideed sung thl 100ratiore o

min Fig. 1 Examples of specimens showing interfacia

millimeters was converted to percentage basedl perimeter of the interface for each specimen.e silicone impression was obtained, each speci-oated with nail polish, except in an area of 1 mm

restoration. They were immersed in 50% AgNO3e dark, followed by a period of 6 h immersion in

solution (Kodak, So Jos dos Campos, SP, Brazil)escent light. After that, the specimens were sec-

0.3-mm diamond discs under water cooling (1000ehler Ltd., Lake Bluff, IL, USA) twice perpendicu-h the center of the restoration. Since some of theance was lost during sectioning (due to the thick-

diamond disc) eight surfaces (rather than fourjacent surfaces) were considered for microleak-ion. Images of each surface were digitized using aying stereomicroscope (model SZ61, Olympus Inc.,n) equipped with a CCD camera (Q-Color 3, Olym-epth of penetration of the tracer was measured

sing the ImageJ software, and both the average of the eight surfaces and the maximum dye pen-

ere recorded. Additionally, the thickness of theer was also recorded.

ymerization stress

(Scotchwith arods wFig. 2).and ththem wcompocylindewas attor themachiheight

Theforce nforce alight gpolishreachi(modeand duexposufor 10tion stress was measured under two compliance dened by the material used as bonding substrateposite: PMMA (high compliance) and glass (low). Rods with 4 mm in diameter were sectioned inith 13 or 28 mm in length. For the 13 mm rods, oneces was polished with silicon carbide sandpaperrit) and felt disks with alumina paste (Aluminaenkirchen, Germany) in order to allow the high-ansmission possible during photoactivation. Therface and both surfaces of the 28 mm rods were

d with aluminum oxide (250 m).PMMA rods, the sandblasted surfaces received aethyl methacrylate monomer (JET Acrlico Autote, Artigos Odontolgicos Clssico, So Paulo,

le the glass rods received a layer of silane (Ceramic ESPE), followed by two layers of unlled resin

Fig. 2 Exptest.se with 13 mm were attached to the lower clampith 28 mm to the upper clamp. The space betweenxed at 1.5 mm (C-Factor: 1.3, volume: 19 mm3). The

were inserted into this space and shaped as alowing the perimeter of the rods. An extensometered to the rods (model 2630-101, Instron) to moni-imen height and provide a feedback to the testing

move the actuator in order to keep the specimen a minimum range.e registered by the load cell corresponded to thesary to counteract the polymerization shrinkageaintain the specimens initial height. The tip of the

(VIP Jr, Bisco) was positioned in contact with therface of the 13 mm rod. The irradiance effectivelye composite was determined using a radiometer, Demetron Res. Corp., Orange, California, EUA)n of the exposure was adjusted to obtain a radiantf 18 J/cm2. Force development was monitoredfrom the beginning of photoactivation and theerimental set up of the polymerization stress

988 d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 984992

Table 2 Means (standard deviation) for bond strength, microleakage, gap and polymerization stress (obtained usingPMMA or glass as bonding substrate). In the same column, means followed by the same letter are statistically similar(one-way ess data, in the same row means followed by thesame low lis/ANOVA, p > 0.05).

Compo kage (mm) Polymerization stress (MPa)

Maximum High compliance Low compliance

Filtek Supr 1.34 (0.21)A 3.5 (0.3)A,b 8.2 (0.6)A,a

Aelite LS P B 1.22 (0.28)A 3.4 (0.5)AB,b 5.0 (0.8)B,a

Filtek Z250 C 1.10 (0.34)AB 2.9 (0.3)ABC,b 5.1 (0.4)B,a

Venus Diam D 0.85 (0.27)BC 2.7 (0.4)BC,a 3.7 (0.3)C,a

Heliomolar CD 0.71 (0.28) C 2.6 (0.6)BC,a 3.3 (0.5) C,a

ELS 0.73 (0.38)C 2.5 (0.3)C,a 2.1 (0.1)D,a

maximum maximum rods (n = 5).

2.4. Sta

PolymerizaANOVA (cMicroleakaKruskalWtests, the p

Pearsontically sign(in both sumicroleakatistically sigcoefcient)(six) and glyses involvdetermine

3. Re

Means andysis for bonmarginal gTable 2.

For bonbetween thand Aelite (ranged fromand four microleakaage and masubsets fofor maximbetween 0.respectivel0.89 mm (E

For polybetween c(p < 0.001). est stress v2.1 MPa) anance: 3.5 MVenus Diam

h compliance levels, while Filtek Supreme, Aelite LS andZ250 presented statistically higher stress values in thempliance system.le 3 presents the Pearsons correlation coefcients (r)n ppend mianceed wtren

prenterfly himpl. Th

Di

sted(on be). F

thosted ticrolsitesel shater

intern broted

3 ANOVA/KruskalWallis, p > 0.05). For the polymerization strer case letter are statistically similar (two-way KruskalWal

site Bond strength (MPa) Marginal gap (%) Microlea

Average

eme 5.1 (2.1)B 47 (5)A 0.89 (0.18)A

osterior 4.7 (2.0)B 42 (6)A 0.78 (0.18)A

6.8 (2.7)AB 27 (4)B 0.62 (0.20)B

ond 7.1 (2.1)AB 13 (3)D 0.45 (0.12)C

6.4 (1.6)AB 20 (5)C 0.44 (0.12)7.9 (3.2)A 21 (7)BC 0.35 (0.14)D

nominal stress was calculated by dividing theforce value recorded by the cross-section of the

tistical analysis

tion stress data were analyzed using two-wayomposite and compliance) and Tukey test.ge and marginal gap were analyzed usingallis due to the lack of homocedasticity. In bothre-set global signicance level was 5%.s tests were used to verify the presence of statis-icant correlations between polymerization stressbstrates, glass and PMMA) and bond strength,ge or marginal gaps. In order to be considered sta-nicant, the critical r value (Pearsons correlation

was 0.811, according to the number of data pairsobal signicance level of 5% [28]. Regression anal-ing the same variables were also performed tothe equations for the regression curves.

sults

standard deviations, as well as the statistical anal-d strength, microleakage (maximum and average),ap and polymerization stress data are shown in

d strength, the only signicant differences weree ELS (7.9 MPa) and both Filtek Supreme (5.1 MPa)4.7 MPa). The percentage of marginal gap incidence

13% (Venus Diamond) to 47% (Filtek Supreme),statistical subsets were observed. Regardingge, composites showed the same ordering for aver-ximum values. However, there were four statistical

on botFiltek low co

Tabbetweeand deage ancomplobtainbond ssystemthree isistentlow cosystemFig. 3.

4.

The testress averagilar topresenand mcompopost-geral, mbetter Also, ipresen

Table

r average microleakage and only three subsetsum microleakage. Maximum microleakage varied71 and 1.34 mm (Heliomolar and Filtek Supreme,y). Average microleakage ranged between 0.35 andLS and Filtek Supreme, respectively).merization stress data, a signicant interactionomposite and compliance level was observedOn both compliance levels, ELS showed the low-alues (high compliance: 2.5 MPa; low compliance:d Filtek Supreme, the highest stress (high compli-Pa; low compliance: 8.2 MPa). ELS, Heliomolar andond presented statistically similar stress values

analyses number othan 0.81

Bond strenMicroleaka

average maximu

Marginal g

Non-signolymerization stress (for both compliance levels)dent variables, namely, bond strength, microleak-arginal gap. For stress data obtained in the low

system, statistically signicant correlations wereith microleakage and marginal gap, but not withgth. Stress data obtained in the high compliancesented statistically signicant correlations with theacial quality tests. Moreover, the r-values were con-gher for correlations involving stress data from theiance system, compared to the high compliancee results of the regression analyses are shown in

scussion

composites ranked similarly for polymerizationoth substrates) and microleakage (maximum andor marginal gap, the ranking was also quite sim-e tests, except for the fact that Venus Diamondhe lowest gap percentage and intermediate stresseakage. Bond strength, however, ranked the tested

in a slightly different order. Based on materialsrinkage and elastic modulus values [10], in gen-ials presenting lower post-gel shrinkage showedfacial integrity, regardless of their elastic modulus.ad terms, materials with low post-gel shrinkage

low stress values for both compliance conditions.

Pearson correlation coefcient (r) for the

presented in this study. Considering thef data pairs analyzed (six), r-values higher1 are statistically signicant.

Polymerization stress

High compliance Low compliance

gth 0.910 0.744*ge

0.993 0.934m 0.942 0.889ap 0.932 0.817

icant, p > 0.05.

d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 984992 989

00,2

0,4

0,6

0,8

1,0A

Ave

rage

mic

role

akag

e (m

m) SUSU

y= r=0

0 10

20

30

40

50

Gap

(%)

y=r=0

02

4

6

8

10

Bon

d S

treng

th (M

Pa)

y=r=

Fig. 3 Regboth compmarginal g

However, amodulus ca

Bond stbetween thof the adheingly, the minuences test that dibonded intthe walls ofound in th

than those found with shear and tensile tests. Therefore, thereis a higher probability of incorporating relatively large defects

adhesult descncese. T

exhus. A

tha) ass

testts th2 4 6 8 10

high compliance low complian ce

EL EL

HM

VDHM VD

FZFZ

y=0,095x + 0,156r=0,934

AEAE

0,498x -0,860 ,993

in the may re

As differeSuprempositesmodulshows(0.35%all thepresenPolymerization Stress (MPa)

2 4 6 8 10

B

HM high co mplian ce lo w co mplian ce

Polymeriza tion Stress (MPa )

VDVD

HM

ELEL

FZFZ

29,33x - 56,956 ,932

AE

SU

AE

SU

y= 5,20x + 4,59 1r=0,817

2 4 6 8 10

high compliance low compl ian ce

Polymeriz ation Stres s (M Pa)

EL EL

HM

VD

HM

VDFZ

FZ

y= -0.432 x + 8.30 6r= -0.74 4

SUAE

SUAE

-2.61 x + 13.93 1 -0.91 0

C

ression analysis of polymerization stress forliance levels and average microleakage (A);aps (B); and bond strength (C).

s it will be discussed below, the inuence of elasticnnot be disregarded.rength values reect the complex interactione bonding substrate and the mechanical propertiessive system and the composite and, not surpris-ethod used to evaluate bond strength signicantlythe results [29]. The main aspect of the push-outfferentiates it from tensile and shear tests in aterfaces is the connement of the composite withinf the prepared cavity, more akin to the conditionse clinic. The bonded area in the push-out is larger

atively highshowed themediate mcompositesmanufactusimilar to t

Composcult to nd in vivo anthat gap inicant correin vivo andlaboratory percentageHeliomolarlow post-gebeen reportpost-gel sh[27], whichof gap form

The masemi-quanto the maxIn the presewas also esive analysMaximum entiate therelatively hof the interthe eight sufound. Theused to quent resultslimitationsused (bovinless of thein dentin tthe formersevere scruanalysis waof the resul

The ave0.55 0.29 mtistically siminuenced Heliomolarsive layer during the specimen preparation, whichin lower bond strength values [30].ribed previously, the only statistically signicant

were found between ELS and Aelite LS/Filtekhis nding may be explained because these com-ibit extreme values of post-gel shrinkage ands shown in Table 1, data from a previous studyt ELS presented the lowest post-gel shrinkageociated with the lowest modulus (2.0 GPa) amonged composites [27]. On the other hand, Aelite LSe highest modulus (9.3 GPa) associated with a rel-

post-gel shrinkage (0.51%), while Filtek Supreme highest shrinkage (0.64%) associated with an inter-odulus (6.0 GPa). It is important to notice that the

considered as low shrinkage by the respectiverers presented bond strength values statisticallyhe conventional composites.ite restorations free of marginal gaps are very dif-clinically [31,32]. A study evaluating gap formationd in vitro for ve different composites observedcidence was always higher in vivo, and a signif-lation could be found between the data obtained

in vitro [32], which increases the relevance ofevaluations. Venus Diamond showed the lowest

of marginal gaps, statistically similar to ELS and. This lower gap formation may be ascribed to thel shrinkage of these composites, and has alreadyed for Venus Diamond [33,34]. Aelite LS presentedrinkage similar to Filtek Supreme and Filtek Z250

could explain the statistically similar percentageation for these composites.jority of studies that evaluated microleakage usedtitative methods (scores) or limited their analysisimum tracer penetration in each specimen [35,36].nt study, the mean microleakage of each specimenvaluated in order to obtain a more comprehen-is of what occurs at the tooth/restoration interface.microleakage presented a lower ability to differ-

materials; in other words, all materials presentedigh dye penetration in at least one of the eight areasface inspected. However, when the microleakage ofrfaces was averaged, more statistical subsets werese ndings suggest that depending on the criteriaantify microleakage, it is possible to have differ-

for the same group of materials. Besides those, microleakage is dependent on the type of teethe or human), and even in the same tooth, regard-

adhesive system, there are more microleakagehan in enamel, due to the higher permeability of

[37]. Though microleakage tests have been undertiny, in the present study a more comprehensives undertaken, trying to increase the consistencyts.rage enamel thickness of the restored cavities was

m. Table 4 shows that enamel thickness was sta-ilar for all groups, so the dye penetration was not

by this factor. As an average, for Venus Diamond, and ELS, most of the dye penetration was restricted

990 d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 984992

Tabl

e

4

Mea

ns

(sta

ndar

d

dev

iation

),

min

imum

and

max

imum

valu

es

for

enam

el

thicknes

s

consider

ing

all t

he

analyz

ed

surfac

es, a

nd

for

thos

e

surfac

es

pre

senting

micro

leak

age

reac

hin

g

beyo

nd

the

enam

el-d

entin

junctio

n

(DEJ

) or

restricted

to

enam

el. A

lso,

the

num

ber

of

surfac

es

pre

senting

micro

leak

age

restricted

to

enam

el

orbo

th

enam

el

and

den

tin

are

show

n. D

istrib

ution

of

surfac

es

pre

senting

micro

leak

age

for

each

spec

imen

(too

th) i

s

pre

sente

d

also

.

Com

pos

ite

Enam

el

thickn

ess

(mm

)*Su

rfac

es

pre

senting

mic

role

akag

e**

Spec

imen

s

pre

senting

mic

role

akag

e

in

(surfac

es)

Ave

rage

Min

imum

Max

imum

Dye

pen

etra

tion

beyo

nd

DEJ

***

Dye

pen

etra

tion

rest

rict

ed

toen

amel

***

Onl

y

inen

amel

Enam

el

and

den

tin

4

or

less

5

6 7

8

Filtek

Supre

me

0.47

(0.2

2)0.

15

0.70

0.55

(0.1

3)

0.40

(0.2

7)

41

79

2

13Ael

ite

LS

Post

erio

r0.

51

(0.1

6)

0.31

0.74

0.47

(0.0

9)

0.55

(0.2

0)

48

72

1

1

13Fi

ltek

Z25

00.

80

(0.4

7)0.

17

1.40

0.67

(0.2

2)

0.88

(0.5

9)

70

50

1

14Ven

us

Dia

mon

d0.

43

(0.2

1)

0.13

0.79

0.42

(0.1

2)

0.44

(0.3

1)

98

22

3

12Hel

iom

olar

0.60

(0.2

6)0.

27

1.00

0.55

(0.1

2)

0.62

(0.3

1)

101

19

1

1

4

9EL

S

0.50

(0.2

6)

0.13

0.98

0.40

(0.0

8)

0.55

(0.3

6)

106

14

3

3

9

Ave

rage

enam

el

thickn

ess

for

the

entire

sam

ple

(n

=

720)

: 0.5

5

(0.2

9)

mm

.

For

each

com

pos

ite,

a

tota

l of

120

surfac

es

was

anal

yzed

(n

=

15, e

ach

spec

imen

with

8

surfac

es).

Ther

e

are

no

stat

istica

l diffe

rence

s

for

the

colu

mn

(ANOVA/o

ne-

way

) or

row

(Stu

den

ts

t

test

) for

the

enam

el

thickn

ess.

to the enamel. As mentioned for bond strength, the lowshrinkage composites showed microleakage values statisti-cally similapresented hand shrinklar to Filtekshrinkage oresulted inwith greatesubset alon

It mustsent two dwell knownpared to dethat increainterface, asequently,

Low shstress valuites. VenusHeliomolarible monommonomer. which assostress devethat the remond and The degreetek Z250, wconversion

Polymerfore, valuesThe testinand dimencomposite obtained vatem was chwere higheFiltek SuprHeliomolarthe lower tthe stress can be explcompositesbonding sulower value

Coincidals chosen shrinkage example, th(Filtek Supage, and vimodulus (Eexplains thstress, regalar rankingbetween stcompliancelation coefcorrelationr to conventional materials. Aelite LS, for example,igh microleakage probably due to its high modulus

age. Venus Diamond presented microleakage simi- Z250. It is possible to assume that, despite the lowf Venus Diamond, its intermediate elastic modulus

a microleakage statistically similar to compositesr shrinkage. ELS stayed on the lower microleakageg with Heliomolar and Venus Diamond.

be pointed out that dentin and enamel repre-ifferent behaviors in terms of compliance. It is

that adhesion to enamel is more reliable com-ntin, but enamel has a higher elastic modulus, andses stress concentration at the enamel-composites already has been demonstrated [3840], and, con-the risk of gap formation and microleakage.rinkage composites presented polymerizationes statistically similar to conventional compos-

Diamond and ELS were statistically similar to and Filtek Z250. Venus Diamond contains a ex-er (TCD-urethane), whereas ELS has no diluent

These features resulted in low elastic modulus,ciated with low post-gel shrinkage reduced theloped by these composites. It is interesting to noticelatively low modulus and shrinkage of Venus Dia-ELS are not due to a lower degree of conversion.

of conversion of these composites is similar to Fil-hile Heliomolar has a relatively lower degree of

. [41].ization stress is not a material property, and there-

vary depending on the testing system used [42,43].g device, bonding substrate, specimen geometrysions, and the adhesive system used to bond theto the substrate may signicantly inuence thelue. In this study, the stiffness of the testing sys-anged only by varying the substrate. Stress valuesr with the stiffer substrate (glass) for Aelite LS,eme and Filtek Z250 but not for Venus Diamond,

and ELS. In a previous study, it was observed thathe elastic modulus of the composite, the closer arevalues obtained in different substrates [23]. Thatained by the fact that in high compliance systems,

with relatively high elastic modulus deform thebstrate in the radial direction, which results in a

registered by the load cell [43].entally, except for Aelite LS, the other ve materi-for this study show a direct relationship betweenand elastic modulus (R2 = 0.72; y = 0.06x + 0.22). Fore material presenting the highest elastic modulus

reme) also presented the highest post-gel shrink-ce versa: the material presenting the lowest elasticLS) presented the lowest post-gel shrinkage. Thise similar ranking of the materials in terms ofrdless of the system compliance [43]. The simi-

on both systems justify the correlations obtainedress and microleakage or gap for both levels of. However, bond strength showed the lowest corre-cient with stress obtained in PMMA and showed no

with the stress obtained in glass. One aspect

d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 984992 991

that differentiates the push-out specimen from the one usedfor microleakage and marginal gap evaluation is that in theformer there was no enamel margins and, therefore, bondingoccurred enBesides, intstress geneby polymereffect.

The ndifferent cmerization(PMMA) areof bonded higher thanlow complimechanicathis ndinga highly rigresponse to

In conclmerizationcan be relastress datacorrelationsystem for a signican

Acknowle

The authorprovided by

r e f e r e n

[1] Hilton reliablyDent 20

[2] Brunthof direcOral In

[3] Manhaa case 2004;23

[4] Ferracacontrac2003;16

[5] Feilzer comporestora

[6] Watts Dshrinkadevelop

[7] Lu H, Sshrinkacompo97986

[8] Sakaguanalysishrinka2004;20

[9] Alster D, Feilzer AJ, de Gee AJ, Davidson CL. Polymerizationcontraction stress in thin resin composite layers as afunctio

ster Dmplintracomatartompoode. arto

scosiress int Mndonrmul00;13ncal. Inress d10;26aga Rvelopsin-c05;21itzel mpomensater 2lheirtweestorancal

comnharracaethodnverstoralheirlymempostorae SY,lyme06;31aga Rntracterfa02;30aro Lbstrata Bincal. Pol

systeemind miling mlues.lin W

vitroemolmpoaro L

Bragodulunt Mtirely on dentin, a more heterogeneous substrate.erfacial debonding is the result of the mechanicalrated by an external load and, though inuencedization stress, it is not a direct consequence of its

dings of the present study suggest that whenompliance levels are compared, composite poly-

stress data generated in a high compliance system more strongly related to the interfacial qualityrestorations, as the correlation coefcients were

those obtained with stress data obtained from aance system. Though direct comparisons betweenl tests and the clinical situation should be avoided,

is likely a reection of the fact that the tooth is notid substrate, demonstrating a high deformability in

polymerization shrinkage [40,44].usion, for the group of materials evaluated, poly-

stress values obtained at both compliance levelsted to interfacial quality in vitro. Nevertheless,

from the high compliance system showed higher coefcients than data from the low compliancemicroleakage and marginal gap formation, besidest correlation with bond strength values.

dgement

s would like to acknowledge the nancial support FAPESP (2008/54456-7).

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Correlation between polymerization stress and interfacial integrity of composites restorations assessed by different in vitro tests