Open Journal of Composite Materials, 2013, 3, 107-112 Published Online October 2013 (
Copyright © 2013 SciRes. OJCM
Effect of Temperatures on Polymerization Stress and
Microleakage of Class V Composite Restorations
Pavinee Padipatvuthikul Didron1*, Wojciech Chrzanowski2, Ayman Ellakwa3,4
1Department of General Dentistry, Srinakharinwirot University, Bangkok, Thailand; 2Faculty of Pharmacy, University of Sydney,
Sydney, Australia; 3Faculty of Dentistry, The University of Sydney, Sydney, Australia; 4Faculty of Dentistry, Tanta University, Tanta,
Email: *
Received July 22nd, 2013; revised August 22nd, 2013; accepted August 31st, 2013
Copyright © 201 3 Pavinee Padipa tvuthikul Didron et al. T his is an open access article distr i bu t e d under the Creative Commons Attribu-
tion License, which permits unrestricted use, distribution, and reproduction in any me dium, prov ided the original work is properly cited.
The loss of interfacial integrity was identified as one of the major causes for replacement of resin com posite restorations.
Preheating procedure has been prov en to enhance flowability and ad aptation of resin composites and increase their de-
gree of conversion. The purpose of this study was to investigate polymerization contraction stress produced in resin
composites after preheating to 37˚C and 60˚C, and measure microleakage of Class V restorations restored with pre-
heated composites. Three resin composites (GC Kalore, Gradia Direct X, Filtek Supreme XT) at room te mpe rature, 3 7˚C,
and 60˚C were investigated. Maximum contraction stress of the composites (n = 5) was evaluated in a modified low-
compliance device. Samples were light-cured for 40 seconds and the maximum force was recorded during 15 minutes.
Calculations were done to adjust for the system’s compliance and obtain linear shrinkage values of composites. Data
were analyzed by Multivariated Analysis of Variance (MANOVA) and Tukey’s test for multiple comparisons (α =
0.05). Seventy-two Class V cavities were prepared on the buccal surfaces of extracted premolars and divided into 9
groups. The teeth were restored with composites at 3 temperatures and were thermo-cycled between 5˚C and 55˚C with
a one-minute dwell-time for 1000 cycles. The teeth were sealed with wax and nail vanish before placed in 0.5% tolu-
idine blue dye for 24 hours. The teeth were embedded in self-curing resin and sectioned bucco-lingually with a
slow-speed diamond saw, providing 3 sections per restoration. Microleakage was rated by two evaluators using a 0 - 4
ordinal scale at the occlusal and cervical margins under light microscope. Microleakage data were analyzed with
Kruskal-Wallis ANOVA and Mann-Whitney U test (α = 0.05). Results indicate that preheating co mposites to 37˚C and
60˚C significantly increased polymerization contraction stress of composites (p < 0.05). A significantly greater amount
of leak age wa s found a t the cerv ical ma rgins (p < 0.05). For all tested materials, preh eating compos ites to 60˚C resulted
in significantly less microleakage at the cervical margin.
Keywords: Preheating; Dental Composite; Polymerization Shrinkage; Contraction Stress; Microleakage
1. Introduction
Improvements in resin composites’ mechanical proper-
ties and their reduced polymerization shrinkage during
the past decade encouraged clinicians to use resin com-
posites more frequently for posterior restorations. Ma-
jorities of improvements aimed to improve microstruc-
ture of the material including monomer composition, size,
shape, and distribution of inorganic filler particles and
targeted mainly at increasing the filler load of resin
composites. However, increasing the filler load resulted
in higher viscosity and led to concerns about handling,
packing, and adaptation of the material. Many attempts
were made to enhance composite adaptation and decrease
microleakage between composites and dental cavity, ei-
ther by using the flowable composite as a base material,
chemical and laser treatments of dentin or by preheating
the composites to lower their viscosity.
The effect of lower viscosity in improvements of adap-
tation has been proven important. Th is is the primary ba-
sis for producing flowable resin composites in which the
lower viscosity can be achieved by decreasing their filler
contents and making changes in the matrix chemistry,
which severely reduce their physical properties. Many
polymers exhibit lower viscosity when they are heated
because thermal vibrations force the composite monomer
further apart and allow them to slide by each other more
*Corresponding a uthor.
Effect of Temperatures on Polymerization Stress and Microleakage of Class V Composite Restorations
Copyright © 2013 SciRes. OJCM
readily. This property leads to a concept of warming or
preheating composite resins before photopolymeriza-
tion, which will decrease the viscosity and increase flow
of resin composites. In addition, composites cured at
elevated temperatures have been proven to increase po-
lymerization rate and have a higher degree of conversion
[1-3], which could result in improved mechanical proper-
ties [4]. Also, it has been reported that increasing com-
posite temperature up to 60 ˚C might enhance the conver-
sion degree on the top and in 2 mm of the bottom sur-
faces [2].
However, it has been reported that the increased de-
gree of conversion associated with preheating would re-
sult in increased polymerization sh rinkage [5]. One study
has shown that temperature has a significant effect on
polymerization shrinkage of microf illed composites. Pre-
heating composites to relatively high temperatures (54˚C
or 68˚C) causes a significant increase in volumetric
shrinkage, but preheating composites to a body tempera-
ture causes similar shrinkage to that at room temperature
[6]. Advantages of preheating the resin are to make more
durable, highly filled, highly viscous conventional com-
posite resin, to reduce the viscosity, to provide flow val-
ues that are similar to those of less filled, flowable resin
composites, without undermining the mechanical proper-
ties. However, more investigation is necessary to deter-
mine the si de effects of preh eating procedu res such as an
increase of the polymerization shrinkage which causes
stress at the tooth/restoration interface and may cause
microleakage of the restorations. The main objective of
this study was to evaluate the effect of preheating on
polymerization contraction stress of composites and the
in vitro marginal microleakage. It was hypothesized that
increasing the preheating temp erature would in crease the
polymerization stress and increase the microleakage at
resin composites/tooth in terfaces.
2. Materials and Methods
2.1. Polymerization Contraction Stress
The materials used in this study are indicated in Table 1.
Polymerization contraction stress was measured by a
modified low-complicance device (Figure 1), consisting
of 2 parts; the first part is a load cell, which a brass steel
piston was attached. A brass steel piston (10 mm diame-
ter; 30 mm length) was used as the bonding substrate for
the composite. The piston had one surface abraded with
#180-grit sandpaper, coated with silane coupling agent
prior to the application of a thin layer of unfilled resin
(Adper™ Single Bond 2), and light-cured for 20 seconds
(MiniLED, Satelec, France). A ringshape teflon mold
was inserted at the end of the brass piston, created a cy-
lindrical cavity (dimension 10 mm diameter × 1 mm
Table 1. Materials used in the present study, their respec-
tive batch number and manufacture r.
Material Batch number
Filtek™ Supreme XTN151598 3M ESPE, Dental Products,
St. Paul MN
GC KALORE™ 910071 GC Corporation,
Tokyo, Japan
Gradia™ Direct X 1201271 GC Corporation, Tok yo,
Adper™ Single Bond 2N283944 3M ESPE, Dental Products,
St. Paul MN
Scotchbond™ EtchantN287300 3M ESPE, Dental Products,
St. Paul MN
Figure 1. The test setup for the polymerization stress meas-
thickness) for resin composite. Uncured resin composite
was preheated and inserted in the mold, the mold was
then removed. The brass piston with the composite was
heated up to specific test temperature on a thermal con-
trolled plate, a thermocouple was placed inside a hole in
the brass piston at all time to measure the composite tem-
The second part is a brass cylinder, holding a clear
perspex disc (22 mm diameter; 1 mm thickness). The
brass cylinder has a slot which allowed for the placement
of the light guide of a curing unit in contact with the
perspex disc. The top surface of perspex disc was abrad-
ed with #180-grit sandpaper, cleaned, coated with a thin
layer of unfilled resin (Adper™ Single Bond 2), and
light-cured for 20 sec. When the desire temperature was
reached, the brass piston was fixed to the load cell. The
brass piston was driven down to just touched the perspex
surface. The composite was photo-activated through the
clear perspex disc. As the composite polymerized, con-
traction force was followed for 15 min. The force values
were converted to nominal stress by dividing them by the
cross-sectional area of the specimen (78.5 mm2). Maxi-
mum contraction stress (Smax) was subjected to statisti-
cal analysis.
Effect of Temperatures on Polymerization Stress and Microleakage of Class V Composite Restorations
Copyright © 2013 SciRes. OJCM
Data were analyzed by Multivariated Analysis of Va-
riance (MANOVA), entering resin composite and tem-
perature as main factors, and Tukey’s test for multiple
comparisons (α = 0.05).
2.2. Microleakage Test
2.2.1. Tooth Selection
Seventy-two extracted caries and restoration-free perma-
nent human premolars were selected, remaining soft tis-
sue removed, and stored in deionized water for a maxi-
mum duration of 4 weeks. The teeth were cleaned with
slurry of pumice and water, rinsed thoroughly with tap
water, and then examined macroscopically with mag-
nification for defects in the enamel and dentin.
2.2.2. Sample Prepa ration
The teeth were randomly assigned into nine groups of
eight. A Class V preparation was made in the buccal sur-
face of each tooth. The occlusal margin of the cavities
were in enamel and the gingival margins located 1.5 mm
apical to the cemento-enamel junction. Preparations were
made with a 329 carbide bur in a high-speed handpiece
equipped with water spray. Cavity dimensions were stan-
dardized (5.0 mm in width, 3.0 mm in height, and 2 mm
in depth). For all groups, enamel and dentin are etched
with 35% phosphoric acid gel (Scotchbond™ etchant,
3M Dental Products, MN, USA) for 20 s and 15 s re-
spectively, rinsed for 20 s, and air-dried to obtain chalky-
white appearance enamel and moist dentin. All cavities
are treated with a resin-based adhesive system. The ad-
hesive used in this study is Adper™ Single Bond 2 (3M
ESPE, St. Paul, MN, USA). Wet-bonding technique is
followed as recommended by the manufacturer, moist
dentin was clinically evidenced by a uniform shiny sur-
face on which water was not pooled. A fully saturated
brush tip for each coat is used, applying two consecutive
coats of Adper™ Single Bond 2 adhesive to prepared
enamel and dentin. Later, the surface was dried gently for
5s and light cured for 20 s (miniLED, Satelec, France).
The cavities were restored as follow:
Group 1: restored with a room temperature Filtek Z350
Group 2: restored with a preheated (37˚C) Filtek Z350
Group 3: restored with a preheated (60˚C) Filtek Z350
Group 4: re stored wi th a room temperature GC Kalore;
Group 5: restor ed wi t h a prehe a te d (3 7˚C) GC Kalore;
Group 6: restor ed wi t h a prehe a te d (6 0˚C) GC Kalore;
Group 7: restored with a room temperature Gradia di-
rect X;
Group 8: restored with a preheated (37˚C) Gradia di-
rect X;
Group 9: restored with a preheated (60˚C) Gradia di-
rect X.
All restorations were done two increments with the
first against the gingival wall, and light-cured for 20 s.
Excess materials are removed with a No.170 bur, fol-
lowed by finishing and polishing with the Softlex disk
system (3M Dental Products Division, St. Paul, MN,
USA). The restored teeth are stored in deionized water at
37˚C for 1 da y before f urther treat ment.
All samples are thermocycled for 1000 cycles between
5 and 55˚C with a dwell time of 1 min, before immersion
in dye. The apices of the teeth are sealed with blue wax
and coated with a nail polish 1 mm short of the restora-
tion margins in order to reduce other leakage elsewhere
that could lead to false positive results. The teeth were
immersed in 0.5% toluidine-blue solution for 24 hour at
room temperature. The superficial dye is removed with a
pumice slurry and rubber cup after removal of the speci-
mens from the dye solution. Teeth are then mounted in a
cold-cure epoxy resin (Leco®, Leco Corporation, MI,
USA) to facilitate handling during sectioning.
2.2.3. Mi croleakag e Test
To measure the extent of microleakage, the teeth were
sectioned longitudinally through the restorations in a
bucco-lingual direction with a low speed diamond saw
(IsoMet™, Buehler Ltd., Lake Bluff, IL, USA), provid-
ing 3 sections per restoration. The sectioned teeth were
evaluated with a stereomicroscope (Leica MZ8, Leica
Microscopy System Ltd., Heerbrugg, Switzerland) at 20
× magnification. The degree of microleakage determined
through dye penetration was scored according to stan-
d ardized criteria (0 to 4; Tab le 2, Figure 2). Double blind-
ed evaluators measured the slices and then the Kappa test
was performed. Differences in the frequency distribution
of scores between groups were assessed using the Krus-
kal-Wallis test and assessments within the groups were
assessed using the Mann-Whitney U test. The results of
testing were analyzed with statistical software (IBM®
SPSS® Statistics Base 21, IBM, USA). Significance is
considered at the 0.05 level.
3. Results
Average polymerization contraction stress of composites
at room temperature and when preheated to 37˚C and
60˚C are shown in Table 3 and Figure 3. Figure 4
shows trend lin es of the polymerization contraction force
during 0 - 60 second. Results indicate that preheating
composites to 37˚C and 60˚C significantly increased po-
lymerization contraction stress and the developmental
rate of polymerization contraction force (p < 0.05). Sta-
tistically greater amount of leakage was found at the cer-
vical margins compared to the occlusal margins (p < 0.05)
for the group restored with composites at room tempera-
ture and the group restored with composites at 37˚C. No
Effect of Temperatures on Polymerization Stress and Microleakage of Class V Composite Restorations
Copyright © 2013 SciRes. OJCM
Table 2. Microleakage scoring criteria.
0 No dye penetration
1 Dye pe netration up to one-half of the cavity wall
2 Dye penetration up to total cavity wall
3 Dye penetration up to one-half of the axial wall
4 Dye penetration more than one-half of the axial wall
Table 3. Average polymerization contraction stress of com-
posites at room temperature and when preheated to 37˚C
and 60˚C.
Materials Room Temp37˚C 60˚C
GC Kalore 4.18 ± 0.02 8.10 ± 0.07 9.85 ± 0.04
Gradia Direct X 5.61 ± 0.02 8.62 ± 0.03 10.72 ± 0.05
Filtek Supreme XT 11.83 ± 0.0114.21 ± 0.05 16.39 ± 0. 05
Figure 2. Diagram of Class V cavity and microleakage scor-
statistical significant differences were observed among
materials and temperatures at the occlusal margin. In
contrast, for all materials tested, the 60˚C preheated sam-
ples showed statistically lower microleakage at the cer-
vical margin. In fact, there was no microleakage ob-
served at the cervical margin for the group restored with
composite preheated to 60˚C.
The polymerization contraction stress results were
analyzed using General Linear Model, Multivariated Ana-
lysis of Variance (MANOVA), Tukey’s and Scheffe’s
Post Hoc test. Highly significant differences were found
both between materials and between temperatures (p <
The frequency distribution of different degrees of mi-
croleakage in the groups is shown in Table 4. There were
significant differences between the microleakage scores
for the enamel and dentin (p < 0.05). Less microleakage
was observed at the occlusal margins than at the cerv ical
margins. Only 2 restorations showed microleakage at the
occlusal margins. There were no significant differences
between materials and temperatures at the occlusal mar-
gins (p > 0.05). However, at the cervical margins, there
Figure 3. Polymerization contraction stress (MPa) of com-
posites at different temperatures.
Figure 4. Polymerization contraction force during 0 - 60
Effect of Temperatures on Polymerization Stress and Microleakage of Class V Composite Restorations
Copyright © 2013 SciRes. OJCM
Table 4. Frequency distribution of micr oleakage for each experimental group.
Occlusal Gingival
Group 0 1 2 3 4 0 1 2 3 4
Group 1: Filtek Supreme (control) 7 1 0 0 0 4 3 0 1 0
Group 2: Filtek Supreme (37˚C) 8 0 0 0 0 5 3 0 0 0
Group 3: Filtek Supreme (60˚C) 8 0 0 0 0 8 0 0 0 0
Group 4: GC Kalore (control) 8 0 0 0 0 5 2 0 1 0
Group 2: GC Kalore (37˚C) 8 0 0 0 0 6 2 0 0 0
Group 3: GC Kalore (60˚C) 8 0 0 0 0 8 0 0 0 0
Group 5: Gradia Direct X (control) 7 1 0 0 0 5 3 0 0 0
Group 6: Gradia Direct X (37˚C) 8 0 0 0 0 6 1 0 0 1
Group 7: Gradia Direct X (60˚C) 8 0 0 0 0 8 0 0 0 0
were significant differences among the preheated groups
(p < 0.05). Preheat composites to 60˚C significantly re-
duced the degree of cervical leakage in all materials
tested. In fact, no microleakage was observed at the cer-
vical margin in this group.
Figure 5 show representative stereomicroscopic im-
ages of the samples with and without cervical microleak-
4. Discussion
The objective of this experimental study was to evaluate
the effect of preheating temperatures on polymerization
contraction stress of composites and to investigate the
extent of in vitro marginal microleakage of Class V resin
composite restoration restored with preheated composites
as compare to the cavity restored with room temperature
composites. The extent of leakage after thermal cycling
is relevant to clinical practice since microleakage of sa-
liva, oral fluids and bacteria at the tooth-restoration in-
terface has been linked causally to a range of problems,
including marginal staining, postoperative sensitivity,
and secondary caries. The integrity and durability of the
marginal seal is an important factor in the longevity of
adhesive dental restorative materials, particularly for com-
posite resins. The absence of a seal at restoration margins
permits the entry of oral bacteria and fluids, which can
result in postoperative sensitivity, adverse pulpal re-
sponses and recurrent caries [7]. In the present study,
standardized methods were used to minimize confound-
ing factors. The dye penetration test is the most widely
used laboratory meth od for assessing leakage, and fo r the
purposes of this study a simple grading system was used
[8]. The apical extent of the test cavities was intention-
ally placed into the root surface because leakage at this
site is known to be a clinical concern when Class II and
Class V cavities are restored with composite resin mate-
The results show that preheating composites signifi-
(a) (b)
Figure 5. Representative stereo-microscopic images of the
cavity with microleakage (a) and without cervical micro-
leakage (b).
cantly increased polymerization contraction stress of
composites and for all materials tested, preheating to
60˚C resulted in significant reduction of microleakage at
the cervical margin. This is agreed with Fróes-Salgado et
al. who evaluated the effect of pre-heating on marginal
adaptation, monomer conversion, flexural strength, mi-
crohardness, and polymer cross-linking of a resin com-
posite under a non-isothermal condition. They found th at
under non-isothermal conditions (similar to a clinical
situation) preheating composite to 68˚C did not improve
the degree of conversion, flexural strength or polymer
crosslinking, but yielded enhanced marginal adaptation
[9]. Wagner et al. also found that preheating composites
can improve adaptation of resin composites to tooth
structure and significantly reduced microleakage, al-
though delay of light curing after placement appears to
be counterproductive and diminishes the positive effects
from the preheating treatment [10]. They also concluded
that flowable liner was less effective than preheating the
composite in reducing microleakage. Interestingly, the
previous expectation that composite preheating could
worsen the marginal adaptatio n of composites to th e cav-
ity walls due to the increased conversion rates [1,2] and
consequently increased polymerization shrinkage [11,12]
Effect of Temperatures on Polymerization Stress and Microleakage of Class V Composite Restorations
Copyright © 2013 SciRes. OJCM
was not confirmed by the results o f the present inv estiga-
tion. The results shows that preheating composite to high
temperatures lead to an increase in polymerization con-
traction stress but less microleakage at the cervical mar-
gin. This is in contrast with several studies that have
shown a direct relationship between contraction stress
and marginal leakage in resin composite restorations
[13-15]. This was also expected because resin compos-
ites exhibit a six to eight ti mes greater thermal expansion
than the surrounding tooth structures [9,16], polymeriza-
tion shrinkage along with thermal contraction might cre-
ate high interfacial stresses in preheated composites upon
thermal equilibrium, with detrimental effects on marginal
adaptation, integrity and seal [13]. Further investigation
is therefore needed regarding advantages and disadvan-
tages of dental composite preheating before we can make
a conclusion if this method is appropriate in dental prac-
5. Conclusion
The present finding suggests that in the challenging
situation of the cervical restoration which extends onto
the root surface, preheating composites to 60˚C signifi-
cantly reduced microleakage at the tooth-restoration in-
terfaces. Preheating however results in non-desirable
increase of polymerization contraction stress. More in-
vestigation should be done regarding the consequence of
the increased stress at the tooth restoration interfaces to
the strength of the restored tooth.
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