• Journal of Technologic Dentistry
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• v.29 no.2
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• pp.9-15
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• 2007

As the development of nanotechnology, the use of composite resins which containing nanofillers becomes popular. The purpose of this study was to test the degree of polymerization of nanofillercontaining composite resins. For the study, three different nanofiller-containing composite resins and two different light-curing units were used. To evaluate the degree of polymerization, the maximum polymerization shrinkage taking place during the light curing, and the microhardness, after the light curing, were measured. As results, two light-curing units exhibited a similar emission spectrum to that of the included photoinitiator, camphorquinone. The only difference between the light-curing units were the width of the emission spectrum. Three different composite resins showed different microhardness values. Among them, Grandio showed the greatest microhardness value. However, there was less microhardness difference on the top and bottom surfaces due to the difference of the light-curing units. The maximum polymerization shrinkage values were also similar in the tested specimens regardless of the difference of the light-curing units. However, Grandio showed the least polymerization shrinkage. According to the manufacturers' data, Grandio showed the highest filler content(vol%).

• Restorative Dentistry and Endodontics
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• v.27 no.2
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• pp.135-141
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• 2002

Objectives : The aim of this study is to evaluate the effect of light intensity variation on the polymerization rate of composite resin using IB system (the experimental equipment designed by Dr. IB Lee) by which real-time volumetric change of composite can be measured. Methods : Three commercial composite resins [Z100(Z1), AeliteFil(AF), SureFil(SF)] were photopolymerized with Variable Intensity Polymerizer unit (Bisco, U.S.A.) under the variable light intensity (75/150/225/300/375/450mW$^2$) during 20 sec. Polymerization shrinkage of samples was detected continuously by IB system during 110 sec and the rate of polymerization shrinkage was obtained by its shrinkage data. Peak time(P.T.) showing the maximum rate of polymerization shrinkage was used to compare the polymerization rate. Results : Peak time decreased with increasing light intensity(p<0.05). Maximum rate of polymerization shrinkage increased with increasing light intensity(p<0.05). Statistical analysis revealed a significant positive correlation between peak time and inverse square root of the light intensity (AF:R=0.965, Zl:R=0.974, SF:R=0.927). Statistical analysis revealed a significant negative correlation between the maximum rate of polymerization shrinkage and peak time(AF:R=-0.933, Zl:R=-0.892, SF:R=-0.883), and a significant positive correlation between the maximum rate of polymerization shrinkage and square root of the light intensity (AF:R=0.988, Zl:R=0.974, SF:R=0.946). Discussion and Conclusions : The polymerization rate of composite resins used in this study was proportional to the square root of light intensity Maximum rate of polymerization shrinkage as well as peak time can be used to compare the polymerization rate. Real-time volume method using IB system can be a simple alternative method to obtain the polymerization rate of composite resins.

• Restorative Dentistry and Endodontics
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• v.27 no.5
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• pp.488-492
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• 2002

The purpose of this study was to evaluate the effectiveness of plasma arc curing (PAC) unit for composite and compomer curing. To compare its effectiveness with conventional quartz tungsten halogen (QTH) light curing unit, the polymerization shrinkage rates and amounts of three composites (Z100, Z250, Synergy Duo Shade) and one compomer, that had been light cured by PAC unit or QTH unit, was compared using a custome made linometer. The measurement of polymerization shrinkage was peformed after polymerization with either QTH unit or PAC unit. In case of curing with the PAC unit, the composite was light cured with Apollo 95E for 6s, the power density of which was recorded as 1350 mW/$\textrm{cm}^2$ by Coltolux Light Meter. For light curing with QTH unit, the composite was light cured for 30s with the XL2500, the power density of which was recorded as 800 mW/$\textrm{cm}^2$ by Coltolux Light Meter. The amount of linear polymerization shrinkage was recorded in the computer every 0.5s for 60s. Ten measurements were made for each material. The amount of linear polymerization shrinkage for each material in 10s and 60s which were cured with PAC or QTH unit were compared with t test. The amount of polymerization shrinkage in the tested materials were compared with 1way ANOVA with Duncan's multiple range test. As for the amounts of polymerization shrinkage in 60s, there was no difference between PAC unit and QTH unit in Z250 and Synergy Duo Shade. In Z100 and Dyract AP, it was lower when it was cured with PAC unit than when it was cured with QTH unit (p<0.05). As for the amounts of polymerization shrinkage in 10s, there was no difference between PAC unit and QTH unit in Z100 and Dyract AP. The amounts of polymerization shrinkage was significantly higher when it was cured with PAC unit in Z250 and Synergy Duo Shade (p<0.05). The amounts of polymerization shrinkage in the tested materials when they were cured with QTH unit were Z250 (6.6um) < Z100 (9.3um), Dyract AP (9.7um) < Synergy Duo Shade (11.2um) (p<0.05). The amount of polymerization shrinkage when the materials were cured with PAC unit were Dyract AP (5.6um) < Z100 (8.1um), Z250(7.0um) < Synergy Duo Shade (11.2um) (p<0.05).

• Restorative Dentistry and Endodontics
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• v.28 no.4
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• pp.354-359
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• 2003

This study evaluated the effectiveness of the light emitting diode(LED) units for composite curing. To compare its effectiveness with conventional quartz tungsten halogen (QTH) light curing unit. the microhardness of 2mm composite. Z250, which had been light cured by the LEDs (Ultralume LED2, FreeLight, Developing product Dl) or QTH (XL 3000) were compared on the upper and lower surface. One way ANOVA with Tukey and Paired t-test was used at 95% levels of confidence. In addition. the amount of linear polymerization shrinkage was compared between composites which were light cured by QTH or LEDs using a custom-made linometer in 10s and 60s of light curing, and the amount of linear polymerization shrinkage was compared by one way ANOVA with Tukey. The amount of polymerization shrinkage at 10s was XL3000 > Ultralume 2. 40. 60 > FreeLight, D1 (P<0.05) The amount of polymerization shrinkage at 60s was XL3000 > Ultralume 2, 60> Ultralume 2.40 > FreeLight, D1 (P<0.05) The microhardness on the upper and lower surface was as follows ; (equation omitted) It was concluded that the LEDs produced lower polymerization shrinkage in 10s and 60s compared with QTH unit. In addition. the microhardness of samples which had been cured with LEDs was lower on the lower surfaces than the upper surfaces whereas there was no difference in QTH cured samples.

• The Journal of Korean Academy of Prosthodontics
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• v.52 no.3
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• pp.195-201
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• 2014

Purpose: This study was designed to compare the amount of polymerization shrinkage of dual-cure resin cements according to different polymerization modes and to determine the effect of light activation on the degree of polymerization. Materials and methods: Four kinds of dual-cure resin cements were investigated: Smartcem 2, Panavia F 2.0, Clearfil SA Luting and Zirconite. Each material was tested in three different polymerization modes: self-polymerization only, immediate light polymerization and 5 minutes-delayed light polymerization. The time-dependent polymerization shrinkage-strain was evaluated for 30 minutes by Bonded-disk method at $37^{\circ}C$. Five recordings of each material with three different modes were taken. Data were analyzed using one-way ANOVA and multiple comparison Scheffe′test (${\alpha}$=.05). Results: All materials, except Panavia F 2.0, exhibited the highest polymerization shrinkage-strain through delayed light-activated polymerization. No significant difference between light activation modes was found with Panavia F 2.0. All materials exhibited more than 90% of polymerization rate in the immediate or delayed light activated group within 10 minutes. Conclusion: As a clinical implication of this study, the application of delayed light activation mode to dual-cure resin cements is advantageous in terms of degree of polymerization.

• Restorative Dentistry and Endodontics
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• v.28 no.6
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• pp.457-466
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• 2003

The aim of study was to investigate the effect of flow, specimen geometry and adhesion on the measurement of linear polymerization shrinkage of light cured composite resins using linear shrinkage measuring device. Four commercially available composites - an anterior posterior hybrid composite Z100, a posterior packable composite P60 and two flowable composites, Filtek flow and Tetric flow-were studied. The linear polymerization shrinkage of composites was determined using 'bonded disc method' and 'non-bond-ed' free shrinkage method at varying C-factor in the range of 1∼8 by changing specimen geometry. These measured linear shrinkage values were compared with free volumetric shrinkage values. The viscosity and flow of composites were determined and compared by measuring the dropping speed of metal rod under constant load. In non-bonded method, the linear shrinkage approximated one third of true volumetric shrink-age by isotropic contraction. However, in bonded disc method, as the bonded surface increased the linear shrinkage increased up to volumetric shrinkage value by anisotropic contraction. The linear shrinkage value increased with increasing C-factor and approximated true volumetric shrinkage and reached plateau at about C-factor 5∼6. The more flow the composite was, reduced linear shrinkage was measured by compensation radial flow.

• Restorative Dentistry and Endodontics
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• v.33 no.4
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• pp.341-351
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• 2008

This study investigated the effect of intermittent polymerization on the rate of polymerization shrinkage and cuspal deflection in composite resins. The linear polymerization shrinkage of each composite was measured using the custom-made linometer along with the light shutter specially devised to block the light at the previously determined interval. Samples were divided into 4 groups by light curing method; Group 1) continuous light (60s with light on); Group 2) intermittent light (cycles of 3s with 2s light on & 1s with light off for 90s): Group 3) intermittent light (cycles of 2s with 1s light on & 1s with light off for 120s); Group 4) intermittent light (cycles of 3s with 1s light on & 2s with light off for 180s). The amount of linear polymerization shrinkage was measured and its maximum rate (Rmax) and peak time (PT) in the first 15 seconds were calculated. For the measurement of cuspal deflection of teeth, MOD cavities were prepared in 10 extracted maxillary premolars. Reduction in the intercuspal distance was measured by the custom-made cuspal deflection measuring machine. ANOVA analysis was used for the comparison of the light curing groups and t-test was used to determine significant difference between the composite resins. Pyramid showed the greater amount of polymerization shrinkage than Heliomolar (p < 0.05). There was no significant difference in the linear polymerization shrinkage among the groups. The Rmax was group 4 < 3, 2 < 1 in Heliomolar and group 3 < 4 < 2, 1 in Pyramid (p < 0.05). Pyramid demonstrated greater cuspal deflection than Heliomolar. The cuspal deflection in Heliomolar was group 4 < 3 < 2, 1 and group 4, 3 < 2, 1 in Pyramid (p < 0.05). It was concluded that the reduced rate of polymerization shrinkage by intermittent polymerization can help to decrease the cuspal deflection.

• Restorative Dentistry and Endodontics
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• v.26 no.4
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• pp.316-325
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• 2001

The purpose of this study was to evaluate the effect of adhesive curing timing on the direction of polymerization shrinkage of light-curing composite resin. In this study, the curing times of adhesive and composite resin were measured by differential scanning calorimeter(DSC). 28 extracted human molars were embedded in clear resin and box-type cavities were prepared. Based on DSC data, the experimental teeth were divided into 4 groups. Group 1: no bond; Group 2: late curing; Group 3: Intermediate curing; Group 4: Early curing. After treating with adhesive, the buccal cavities were filled with Z-100 hybrid composite resin and the lingual ones were filled with AEliteflo flowable composite resin. The depressions at the surface were measured by surface profilometer, then the specimens were embedded in clear resin and sectioned. Impressions were obtained and used to get epoxy resin replicas. The epoxy replicas were gold-coated and observed under SEM. Average Maximum Gap(AMG), Gap Proportion(GP), Average Marginal Index(AMI) were used to compare the shrinkage gap of each group. The results were statistically analyzed using the Kruskal-Wallis One Way ANOVA, Student-Newman-Keuls method. The results of this study were as follows. 1. Average Maximum Gap, Gap Proportion, Average Marginal Index and depression at the surface or Z-100 hybride composite resin were smaller than those of AEliteflo flowable composite resin(P<0.05). 2. When the bonding between composite resin and tooth structure was strong, the shrinkage gap was small, and depression at the surface was deep(P<0.05). 3. In the well-bonded group, light-curing composite resin shrank toward bonded cavity wall, not toward light source. The result suggested that the direction of polymerization shrinkage was affected by the quality of bonding in the dentin-resin interface. The strong was the bonding between composite resin and tooth structure, the smaller was the gap and the deeper was the depression at the surface. Then the flow to compensate the polymerization shrinkage proceeded from surface to bonded cavity wall.

• Proceedings of the KACD Conference
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• 2003.11a
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• pp.613-613
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• 2003

The purpose of this study was to compare the effect of exponential curing method with conventional curing and two step soft start curing method on polymerization shrinkage of composite resins. Three brands of composite resins (Synergy Duo Shade, Z-250, Supreme) and three brands of light curing units (Spectrum 800, Elipar Highlight, Elipar Trillight) were used. In this study, the diameter of specimen was 5.5mm and height 1.6mm and the specimen was cured for 40 seconds. The shrinkage was measured by custom made linometer. The amount of linear polymerization shrinkage recorded in the computer every 0.5 second for 90 seconds. Each group was measured 10 times.(omitted)

• Composites Research
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• v.26 no.3
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• pp.182-188
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• 2013

The purpose of this study was to measure the volumetric polymerization shrinkage kinetics and stress of a silorane-based dental restorative composite and compare it with those of conventional methacrylate-based dental composites. Two methacrylate-based composites (Z250, Z350 flowable) and one silorane-based composite (P90) were investigated. The volumetric polymerization shrinkage of the composites during light curing was measured using a laboratory-made volume shrinkage measurement instrument based on the Archimedes' principle, and the polymerization stress was also determined with the strain gage method. The shrinkage of silorane-based composites (P90) was the lowest, and that of Z350 flowable was the highest. Peak polymerization shrinkage rate was the lowest in P90 and the highest in Z350 flowable. The time to reach peak shrinkage rate of P90 was longer than those of the methacrylate-based composites. The polymerization shrinkage stress of P90 was lower than those of the methacrylate-based composites.