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Polymerization shrinkage ofrestorative resin-based com-posites has been associatedwith microleakage, debonding,

secondary caries and postoperativesensitivity.1-5 Among the techniquessuggested to reduce polymerizationshrinkage stress is the incrementalplacement of composite material, inwhich the clinician typically placesthe material in small increments of 2 millimeters or less and then photo -activates it from an occlusal direc-tion.6,7 Although the incremental tech-nique may be necessary for adequatelight penetration, its disadvantagesinclude the possibility of trappingvoids or contamination between layersand the increased time required toplace the restoration. The benefit ofusing an incremental technique forreducing shrinkage stresses has beenquestioned on the basis of numericaland experimental analyses.8,9 Idrissand colleagues10 found no significantdifference between bulk and incre-mental filling techniques when theyexamined marginal gap size in ClassII composite restorations in vitro.

Besides filling techniques, thedirection of shrinkage also often isregarded as an important factor incontrolling shrinkage patterns in res-torations. It once was believed thatresin-based composite shrinks towardthe source of light and thus could bemanipulated to obtain a beneficialshrinkage orientation during photo-

Dr. Campodonico was a postdoctoral student, Postgraduate Program in Contemporary Restorative and Esthetic Dentistry, School of Dentistry, University of Minnesota, Minneapolis, when this article was written. He now maintains a private practice in general and cosmetic dentistry in Blaine, Minn.Dr. Tantbirojn is an associate professor, Department of Restorative Dentistry, College of Dentistry, University of Tennessee Health Science Center, Memphis.Dr. Olin is an associate professor, Department of Restorative Sciences, Division of Prosthodontics, School of Dentistry, University of Minnesota, Minneapolis.Dr. Versluis is a professor, Department of Bioscience Research, College of Dentistry, University of Tennessee Health Science Center, 875 Union Ave., Memphis, Tenn. 38163, e-mail “antheun@uthsc.edu”. Address reprint requests to Dr. Versluis.

Cuspal deflection and depth of cure in resin-based composite restorationsfilled by using bulk, incremental and transtooth-illumination techniques Carlos E. Campodonico, DDS; Daranee Tantbirojn, DDS, MS, PhD; Paul S. Olin, DDS, MS; Antheunis Versluis, PhD

AB ST RACTBackground. Restoration techniques affectshrinkage stress and depth of cure. The authorstested cuspal deflection and depth of cureresulting from the use of different techniques(bulk, incremental, bulk/transtooth illumination) andtwo resin-based composites (deep curing and conventional).Methods. The authors restored extracted teeth with deep-curingX-tra fil (VOCO, Cuxhaven, Germany) (by using bulk and incre-mental techniques) and Filtek Supreme Plus (3M ESPE, St. Paul,Minn.) (by using bulk, incremental and bulk/transtooth-illumina-tion techniques). The sample size for each technique was five. Theydetermined cuspal deflections as changes in buccal and lingual sur-faces before and after restoration. To determine the extent of cure,they measured hardness 0.5 to 3.5 millimeters deep on the sec-tioned restorations. Results. The authors found no difference in cuspal deflectionbetween filling techniques within the same materials (P > .05).They found no difference in hardness for X-tra fil at any depth witheither the bulk or the incremental technique (P > .05). FiltekSupreme Plus had higher hardness values at depths of less than 1.5 mm with the bulk/transtooth-illumination technique, whereasthe bulk technique resulted in lower hardness values at depths of2.0 mm and below (P < .05). Conclusions. Cuspal deflection was not affected by filling tech-niques. X-tra fil cured up to a depth of at least 3.5 mm; FiltekSupreme Plus had lower curing values below a depth of 2 mm. Thetranstooth-illumination technique improved curing depth for resto-rations placed in bulk.Clinical Implications. When using resin-based compositerestorative materials, clinicians should be more concerned aboutthe effect of filling techniques on curing depth than about howthese techniques affect shrinkage stresses.Key Words. Composite; cuspal flexure; cure; bulk; increment;transtooth illumination; hardness.

JADA 142(10):1176-1182.

© 2011 American Dental Association. Republished by Medical Online Publication SAL with permission of American Dental Association. All rights reserved. JADA 2011, Volume 142, No 10, Page 1176-1182

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activation. Versluis and colleagues11

pointed out that composite does notshrink toward the light and that,rather, the direction of shrinkage isdetermined predominantly by the pres-ence or absence of a bond. This obser-vation has been helpful for rational-izing curing protocols. Belvedere12

proposed that a transenamel illumina-tion technique involving light curing ofa bulk-placed composite from buccaland lingual directions, and thusthrough the tooth enamel, can achievethe advantages of bulk placementwhile avoiding the disadvantages ofincremental techniques. Light transmittedthrough the tooth structure initially polymerizesthe most critical areas along the interfaces,establishing adequate bonding before polymer-ization shrinkage of the inner bulk interferes.12

Although low residual stress and good adapta-tion are important, thorough polymerization is anequally important consideration for any fillingtechnique. The main concern regarding a bulktechnique is whether the composite cures fullyenough in the deeper portions to create a materialthat has acceptable physical and biocompatibleproperties. Using microhardness at various resto-ration depths as an indicator, Lazarchik and col-leagues13 showed that the extent of polymeriza-tion was not different between bulk-filled andincrementally filled restorations of a light-shadecomposite, whereas the bulk technique resultedin significantly lower microhardness values in amaterial of a darker shade. However, Amaral andcolleagues14 found no difference in microhardnessat any depth between the bulk-placed or incre-mentally placed restorations, provided that therestorations were exposed to light from occlusal,buccal and lingual directions. Thus, thetranstooth-illumination technique also may over-come the concern regarding depth of cure that isassociated with bulk placement.

We conducted an in vitro study to investigatewhether a bulk-placement technique affectsshrinkage stress, and whether the clinician canprevent a compromised depth of cure by using amore deeply curing composite or by using thetranstooth-illumination technique. Becauseshrinkage stress itself cannot be measureddirectly, we assessed its effect by measuringcuspal deflection of restored teeth. We assessedthe extent of cure by measuring microhardnessat vari ous depths. To compare the effect ofshrinkage stress between bulk-restored andincrementally restored teeth, we used a com-posite designed to cure up to a depth of 4 mm.

Figure 1. A. Mounted tooth in custom-made stainless steel ring with referencespheres. B. Cavity preparation, digitized with the LavaScan ST optical scanningsystem (3M ESPE, St. Paul, Minn.). Image B reproduced with permission of 3M ESPE.

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This provided sufficient depth of cure to allowcomparison of shrinkage stress effects from thetwo techniques. We used a conventional com-posite to compare the effects of transtooth illumi-nation of a restoration placed in bulk with con-ventional bulk and incremental techniques.

METHODSWe chose for the study a hybrid composite that itsmanufacturer claims has a curing depth of 4 mm(X-tra fil, Universal shade, VOCO, Cuxhaven,Germany) and a nanocomposite (Filtek SupremePlus, A2D shade, 3M ESPE, St. Paul, Minn.).

Sample preparation and digitization.The study protocol, which the institutionalreview board of the University of Minnesota,Minneapolis, designated as exempt, involved theuse of 25 extracted human teeth. We secured theteeth in stainless steel rings (Figure 1A) andkept them immersed in water throughout theprotocol to prevent desiccation. Each ring con-tained four embedded spheres surrounding thetooth sample, which functioned as stable refer-ence areas. We sandblasted the spheres andetched the tooth enamel with 37 percent phos-phoric acid solution to obtain dull surfaces suit-able for optical scanning.

We prepared a large, slot-shaped mesioocclu-sodistal cavity (4 mm deep, 4 mm buccolingualwidth) with a no. 245 carbide bur in a high-speed handpiece under copious amounts ofwater. The mean (standard deviation [SD]) wallthickness, measured at the middle of the resto-ration wall, was 2.39 (0.34) mm. After prepara-tion, we digitized images of the teeth along withtheir reference spheres with an optical scanningsystem (LavaScan ST, 3M ESPE); the digitalmodels had an estimated resolution of 60 micro -meters and 5-μm accuracy (Figure 1B). We cali-brated the scanner each day before conductingthe experiments.

ABBREVIATION KEY. TT: Transtooth.

A B

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Experimental groups. We carried out twoindependent sets of experiments, one in whichwe restored teeth with X-tra fil and the other inwhich we restored teeth with Filtek SupremePlus. We determined the sample size needed toenable us to detect a mean difference of one SDwith a 95 percent confidence, on the basis ofprevious studies in which investigators used thesame methodology.15,16

X-tra fil. We divided 10 teeth (six premolarsand four molars) to be restored with X-tra fil intotwo groups (each n = 5) of matched pairs forshape and size; hence, each group containedthree premolars and two molars. We filled eachpair randomly with an incremental or a bulktechnique. There was no significant difference inwall thickness between the two groups (P = .05).

Filtek Supreme Plus. We divided 15matched premolars to be restored with FiltekSupreme Plus into three groups (each n = 5). Werandomly filled the sets of three matched teethwith a bulk, an incremental or a transtooth-illumination bulk technique. There was no sig-nificant difference in wall thickness between thethree groups (P = .05).

Filling and curing techniques. For the bulktechnique, we placed the composite in one incre-ment (4 mm) and light cured it for 40 seconds (20 seconds from the occlusobuccal direction and20 seconds from the occlusolingual direction). Forthe incremental technique, we placed the com-posite in two horizontal increments approxi-mately 2 mm thick and light cured it for 20 sec-onds (10 seconds from the occlusobuccal directionand 10 seconds from the occlusolingual direction).

For the bulk/transtooth-illumination technique,we placed the composite in one increment (4 mm)and light cured it for 20 seconds simultaneouslywith two curing lights through the buccal and lin-gual surfaces, followed by 20 seconds from theocclusal direction. We used two high-intensitycuring units (CureMax V LED Curing Light,Maximum Dental, Secaucus, N.J., and AllegroHigh-Intensity LED, Den-Mat, Santa Maria,Calif.). The light intensities, measured with theradiometer built into the Allegro charging unit,were 1,238 milliwatts per square centimeter and1,294 mW/cm2, respectively.

Bonding protocol. We used the samebonding protocol in each technique. We etched thecavity surfaces with 34 percent phosphoric acid(Caulk 34% Tooth Conditioner gel, DentsplyCaulk, Milford, Del.) for 15 seconds, rinsed themwith water for 10 seconds, blotted them dry,applied Prime & Bond NT (Dentsply Caulk) for20 seconds, lightly air dried them for five secondsand light cured them for 20 seconds. After we fin-ished the restorations, we wiped the compositesurfaces with an alcohol pad to remove theoxygen-inhibition layer. We did not polish the res-torations. Immediately after restoration, we digi-tized the teeth in the LavaScan system.

Cusp flexure analysis. We accuratelyaligned the digitized tooth surfaces before andafter restoration by using Cumulus software(copyright Regents of the University of Min-nesota), fitting the stainless steel referencesphere surfaces in three dimensions.17 By usinga custom-developed software (CuspFlex), we cal-culated contour changes perpendicular to theoriginal tooth surfaces. We selected the buccaland lingual surfaces above the gingival level ofthe restoration up to the cusp ridges as the areassubjected to cuspal deflection. We defined cuspaldeflection as the difference between the restoredtooth and the prepared tooth, determining thedifferences perpendicular to the buccal or lingualsurfaces. A linear color scale was used to visu-alize changes in the tooth surfaces (Figure 2).We determined the average cuspal deflection ofeach surface by calculating the notional volumechange (difference integrated over the buccaland lingual surfaces) divided by the surfacearea. The coronal deformation was the sum ofbuccal and lingual cuspal deflections.15,16

Microhardness determination. After scan-ning, we cross-sectioned the restored teeth bucco-lingually at the highest point of the cusp, perpen-dicular to the long axis of the tooth. We embeddedthe two halves in Orthodontic Resin (LD Caulk,Milford, Del.), and we polished the cross-sectionedsurfaces serially by using a grinder-polisher

Figure 2. Coronal deformation as seen on Cumulus software(copyright Regents of the University of Minnesota, Minneapolis),with the reference spheres. The color scale in red, yellow andgreen shows the cusp movement toward the center of the tooth.

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(EcoMet 3 Grinder-Polisher, Buehler, Lake Bluff,Ill.) and 400- and 600-grit silicon carbide paper(Buehler), followed by 1.0-μm and 0.05-μm alu-mina suspensions (Buehler).

We measured microhardness of the compositerestorations by using a hardness tester (MicroMet5104, Buehler) with a Vickers indentor at 200gload. We made a series of indentations along thelong axis of the tooth in the center of the restora-tion at 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 and 3.5 mm fromthe occlusal surface. We evaluated both halves ofthe restorations. The hardness value at eachdepth was the average of both sides.

Statistical analysis. To analyze the differ-ences between the filling techniques for coronaldeformation and for microhardness at each depth,we used the t test for X-tra fil and one-way analy -sis of variance (ANOVA) followed by the Student-Newman-Keuls (SNK) post hoc test for FiltekSupreme Plus. In addition, we analyzed the hard-ness differences among various depths for thesame filling technique and the same composite byusing one-way ANOVA followed by the SNK test.We performed all statistical analyses at a signifi-cance level of .05. We made no comparisonbetween X-tra fil and Filtek Supreme Plus.

RESULTSCuspal deflection. The cusps of all teethmoved inward after restoration (Figure 2). Ingeneral, Filtek Supreme Plus caused morecuspal deflection than did X-tra fil. Table 1 liststhe coronal deformation values, defined as thesum of the buccal and lingual cuspal deflectionvalues. We found no significant differenceamong the filling techniques within the samecomposite material (P > .05).

Microhardness. Table 2 and Figure 3 (page1181) show the measured microhardness valuesof the restorations at various depths. In general, X-tra fil restorations had hardness values higherthan those of Filtek Supreme Plus. Figure 3 con-tains statistical results of the hardness differ-ences among filling techniques (within the samecomposite material) at each depth. For X-tra fil,we found no significant difference between thebulk and incremental techniques at any depth (P > .05). For Filtek Supreme Plus, the hardnessvalues of composite restored with the bulk/transtooth-illumination technique were signifi-cantly higher than those of composite restoredwith the bulk or incremental techniques atdepths of 0.5, 1.0 and 1.5 mm, and the hardnessvalues of composite restored with the bulk tech-nique were significantly lower than those of com-posite restored with the bulk/transtooth-illumination or incremental techniques at depths

of 2.0, 2.5, 3.0 and 3.5 mm (P < .05). The bulk/transtooth-illumination technique tended to pro-duce hardness values higher than those of theother two techniques.

Table 2 contains statistical results of the hard-ness differences among various depths for eachfilling technique. For X-tra fil, there was no sig-nificant difference in hardness between variousdepths for either filling technique (bulk or incre-mental, P > .05). For Filtek Supreme Plus, wefound some differences between hardness valuesat various depths with all filling techniques. In Filtek Supreme Plus restorations placed withthe bulk technique, hardness values at 2.5, 3.0and 3.5 mm were significantly lower than thoseat 0.5 and 1.0 mm (P < .05). The hardness profilein the Filtek Supreme Plus group restored incre-mentally showed values decreasing between 0.5and 1.5 mm, increasing at 2.0 mm and then de -creasing again. Hardness values at 3.0 and 3.5 mm were significantly lower than those at 0.5 mm. In Filtek Supreme Plus restorationsplaced with the bulk/transtooth-illuminationtechnique, the hardness values at 3.0 and 3.5 mmwere significantly lower than those at 0.5 mm (P < .05), and the hardness values from 0.5 to 2.5 mm were not significantly different (P > .05).

DISCUSSIONPolymerization shrinkage has been of major con-cern to dental clinicians placing direct compositerestorations in posterior teeth. On the one hand,a good adhesive seal helps prevent microleakageand ensure that the composite will reinforce thetooth structure, but, at the same time, such abond will constrain polymerization shrinkage andthus induce stresses in the tooth structure. Use of

TABLE 1

Mean (standard deviation) coronaldeformations (sum of buccal and lingual cuspal flexure).MATERIAL ANDTECHNIQUE

DEFORMATION(MICROMETERS)

X-tra fil*

Bulk 15.6 (1.1)a†

Incremental 15.0 (3.7)a

Filtek Supreme PlusBulk 16.2 (1.7)a

Incremental 17.7 (1.9)a

Bulk/transtooth illumination 17.3 (2.9)a

* X-tra fil is manufactured by VOCO, Cuxhaven, Germany.† Same letters denote mean values that were not significantly

different within the same resin-based composite material(according to t test for X-tra fil and analysis of variance/Student-Newman-Keuls post hoc test for Filtek Supreme Plus [3M ESPE,St. Paul, Minn.], P > .05).

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bulk placement has been suggested to producelower shrinkage stresses,8 but sufficient depth ofcure may require an incremental technique.

Bulk versus incremental placement.Shrinkage stresses. First, we tested the effectof bulk versus an incremental technique onshrinkage stresses by recording cuspal deflec-tion. Often, clinicians fill deep restorations inmore than two increments. Additional incre-ments may increase the cuspal deflection owingto accumulation of incremental deformations ofthe weakened cavity walls,8 but they still can benecessary to ensure good cure and bonding. Wechose a two-layer incremental method because 2 mm usually is regarded as the maximumthickness for curing a composite and becausethe placement procedure was more controllableand thus more consistent. We found no signifi-cant difference in cuspal deflection between thebulk and incremental methods. Although deflec-tion is not a stress itself, it is a manifestation ofinternal stress conditions within a tooth. Forsimilar tooth and restoration shapes and prop-erties, cuspal deflection provides a reasonablereflection of internal stresses. We obtained com-parable shapes by matching teeth and standard-izing cavity sizes, and we assumed tooth proper-ties to be similar. To ensure similar compositeproperties in both bulk and incrementally filledrestorations, we used X-tra fil composite, whichthe manufacturer claims can cure to a depth ofas much as 4 mm. The microhardness valuesconfirmed that curing levels with both methodswere similar at all depths, and they showed nostatistically significant differences (Table 2 andFigure 3A). The X-tra fil thus delivered the deepcuring claimed by the manufacturer regardlessof filling technique. Given that the conditionsand cure were similar between the bulk and

incrementally filled restorations and that thecuspal deflections were not significantly dif-ferent, we conclude that differences in shrinkagestresses between the bulk and two-layer incre-mental placement methods could not have beensubstantial.

Curing depth. If the difference in shrinkagestress between bulk and incremental techniquesthus was not a major issue, the next question iswhether adequate cure could be ensured with abulk technique. To test this, we used FiltekSupreme Plus, which the manufacturer recom-mends using in increments of no more than 2 mmthick. We compared conventional bulk and incre-mental techniques with a bulk/transtooth-illumination technique, which has been reportedto cure the deep part of a restoration effectively.12

The cuspal deflection results did not show signifi-cant differences among the three curing tech-niques. However, microhardness, which within aresin-based material has a good correlation withdegree of cure for a broad range of conversionlevels,18-20 was affected by the different fillingtechniques. For the conventional bulk technique,we noted a continuous drop in the hardnessvalues as the depth increased (Figure 3B). At 2.0 mm and below, hardness values of FiltekSupreme Plus applied in the bulk technique weresignificantly lower than those of the samematerial placed with the incremental andbulk/transtooth-illumination techniques. Thisconfirms the general concern that a conventionalbulk technique compromises depth of cure andthe consequent recommendation for incrementalmethods. Since light attenuation in composite isthe same regardless of whether the material wasplaced in bulk or with an incremental technique,the hardness values of material placed with theincremental technique followed the same con-

TABLE 2

Mean (standard deviation) Vickers hardness numbers at various depths. MATERIAL ANDTECHNIQUE

VICKERS HARDNESS NUMBER AND DEPTHS IN MILLIMETERS

0.5 1.0 1.5 2.0 2.5 3.0 3.5

X-tra fil*

Bulk 121.8 (10.1)a† 118.2 (12.7)a 117.3 (7.9)a 115.3 (4.8)a 112.1 (6.4)a 115.2 (8.9)a 111.1 (5.5)a

Incremental 121.9 (18.2)a 117.78 (8.5)a 116.2 (10.4)a 117.8 (5.3)a 118.1 (2.4)a 113.5 (9.2)a 114.9 (10.3)a

Filtek Supreme Plus‡

Bulk 101.3 (1.7)a 101.12 (1.7)a 97.2 (4.5)a,b 93.1 (4.4)a,b,c 88.5 (5.9)b,c 83.0 (6.3)c,d 75.1 (12.9)d

Incremental 102.3 (1.8)a 99.8 (4.5)a,b 95.6 (4.8)a,b,c 100.2 (3.9)a,b 97.3 (2.6)a,b 94.9 (3.1)b,c 90.6 (4.2)c

Bulk/transtoothillumination

107.4 (5.2)a 106.9 (3.3)a 106.5 (2.9)a 104.0 (3.8)a 101.3 (1.7)a,b 98.3 (2.3)b,c 95.0 (3.4)c

* X-tra fil is manufactured by VOCO, Cuxhaven, Germany.† Same letters denote mean values that were not significantly different among depths within the same resin-based composite material and tech-

nique (according to analysis of variance/Student-Newman-Keuls post hoc test, P > .05). ‡ Filtek Supreme Plus is manufactured by 3M ESPE, St. Paul, Minn.

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tinuous drop as found in material placed with thebulk technique, except that there was a stepincrease at a depth of 2.0 mm (Figure 3B). Thestep increase in hardness at 2.0 mm correspondedwell with the boundary between the first andsecond increments and thus represented thesuperficial composite of the first increment, whichreceived more light energy (and higher cure) thanthe deeper composite of either increment. Incre-mental techniques thus improved the overall curewithin a restoration.

Transtooth illumination. Little publishedinformation exists about the effectiveness oftranstooth-illumination techniques. Althoughthere is some skepticism about the effectivenessof techniques that involve curing through toothstructure, investigators in two studies reportedthat light could penetrate enamel and dentinwalls and cure the inner portion of a restorationwith no difference compared with the incrementaltechnique, provided that the composite was curedfrom the buccal, lingual and occlusal direc-tions.13,14 In this study, we found that FiltekSupreme Plus restorations had significantlyhigher hardness when we used a bulk/transtooth-illumination technique than when we used theconventional bulk technique and also had signifi-cantly higher hardness values up to a depth of 1.5mm than did restorations placed with an incre-mental technique (Figure 3B). In addition, thehardness values did not drop significantly until adepth of 3.0 mm (Table 2), which suggests a goodoverall polymerization. The superior performanceof the transtooth-illumination technique in ourstudy could be a result of the ability of light topenetrate enamel walls,13 or it simply could arise

from the fact that the amount of light energyapplied with this technique was higher. In thebulk/transtooth-illumination technique, we curedthe material for 20 seconds simultaneously withtwo curing lights through the buccal and lingualsurfaces, followed by curing for 20 seconds fromthe occlusal direction (total, 60 seconds), whereasfor the bulk and incremental techniques we curedfor 20 seconds from the occlusobuccal and for 20seconds from the occlusolingual direction (total,40 seconds). Note that the light sources we usedin the study were current-generation curinglights with high outputs that could cure ad -equately through the tooth structures. Thebulk/transtooth-illumination technique resultedin coronal deformation values that were slightlyhigher than those found with the incremental andbulk techniques, but these were not statisticallysignificantly different (Table 1). Therefore, therewas no indication that the extra energy applied inthe bulk/transtooth-illumination technique hadincreased shrinkage stresses significantly.

Hardness values. There is no clear consensusabout how much conversion should be consideredadequate. A bottom-to-top hardness ratio of 0.8represents a bottom-to-top degree of cure of 0.9and may be considered adequate curing.21 In thisstudy, we found that when cured with a conven-tional bulk technique, a Filtek Supreme Plus res-toration at depths of 3.0 and 3.5 mm had hard-ness values lower than about 80 percent of thevalue at 0.5 mm depth, whereas with an incre-mental or bulk/transtooth-illumination technique,values at all measured depths were higher than80 percent. X-tra fil had relative hardness valueshigher than 90 percent at all depths, regardless of

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Figure 3. Vickers hardness numbers at various depths in the restorations: A. X-tra fil (VOCO, Cuxhaven, Germany) and B. FiltekSupreme Plus (3M ESPE, St. Paul, Minn.). Same letters denote mean values that were not significantly different between filling tech-niques at the same depth (t test for X-tra fil and analysis of variance and Student-Newman-Keuls post hoc test for Filtek Supreme Plus, P > .05). mm: Millimeters. TT: Transtooth (illumination technique).

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the filling technique used. Note that we could notcalculate a bottom-to-top ratio because our hard-ness measurements started at 0.5 mm below thetop surface. Readers also should be aware that wesectioned, embedded and polished the compositerestorations to achieve a surface suitable formicrohardness measurements. Any of these pro-cedures could have increased the hardnessvalues. Cheng and Douglas22 found that hardnessvalues increased more than 25 percent after res-torations underwent polishing. Thus, hardnessvalues of clinical restorations with the compositeschosen for this study may be lower than thevalues reported here. On the other hand, clinicalvalues could turn out to be higher for a lessopaque shade of Filtek Supreme Plus that mostclinicians prefer because it cures better than therelatively opaque A2D shade used in this study.13

We selected the A2D shade to allow the LavaScanST optical scanner to digitize the restoration.

In summary, the effect of different fillingtechniques on cuspal flexure was not significantin this study. Although shrinkage stress levelscannot be simply extrapolated from cuspalflexure, the results of our study suggest that cli-nicians should be more concerned about a thor-ough cure of a restoration than about placementtechnique. Long-term performance of a restora-tion is likely to depend more on the quality andphysical properties of a restoration than on theminor differences in initial shrinkage stressescaused by placement techniques.

CONCLUSIONSWithin the limitations of this in vitro study, weconclude that the filling techniques we usedresulted in no significant difference in theamount of cuspal deflection between the com-posites we evaluated.

We found that X-tra fil had adequate curingup to at least 3.5 mm when placed in one bulkincrement, with no significant difference inhardness from that of X-tra fil placed with theincremental technique.

Filtek Supreme Plus had lower hardnessvalues, and thus a lesser extent of cure, whenrestored with bulk technique than when restoredwith the incremental or bulk/transtooth-illumination techniques. In addition, the bulk/transtooth-illumination technique producedhigher hardness values in the superficial layer ofthe Filtek Supreme Plus in comparison with theincremental technique.

The transtooth-illumination technique, whichrequires light curing from buccal, lingual andocclusal directions, can improve the depth ofcure of composites placed in bulk without

increasing cuspal deflection. ■

Disclosure. None of the authors reported any disclosures.

This study was supported in part by Non-tenured Faculty Grants toDrs. Versluis and Tantbirojn from the 3M Foundation, St. Paul, Minn.

The authors thank David G. Augustson for his technical support.

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6. Feilzer AJ, De Gee AJ, Davidson CL. Setting stress in compositeresin in relation to configuration of the restoration. J Dent Res 1987;66(11):1636-1639.

7. Giachetti L, Scaminaci Russo D, Bambi C, Grandini R. A reviewof polymerization shrinkage stress: current techniques for posteriordirect resin restorations. J Contemp Dent Pract 2006;7(4):79-88.

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