• Restorative Dentistry and Endodontics
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• v.32 no.1
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• pp.28-36
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• 2007

The purpose of this study was to compare the effect of exponential curing method with conventional curing and soft start curing method on polymerization shrinkage of composite resins. Three brands of composite resins (Synergy Duo Shade, Z250, Filtek Supreme) and three brands of light curing units (Spectrum 800, Elipar Highlight, Elipar Trilight) were used. 40 seconds curing time was given. The shrinkage was measured using linometer for 90 seconds. The effect of time on polymerization shrinkage was analysed by one-way ANOVA and the effect of curing modes and materials on polymerization shrinkage at the time of 90s were analysed by two-way ANOVA. The shrinkage ratios at the time of 20s to 90s were taken and analysed the same way. The results were as follows : 1. All the groups except Supreme shrank almost within 20s Supreme cured by soft start and exponential curing had no further shrinkage after 30s (p < 0.05). 2. Statistical analysis revealed that polymerization shrinkage varied among materials (p = 0.000) and curing modes (p = 0.003). There was no significant interaction between material and curing mode. 3. The groups cured by exponential curing showed the statistically lower polymerization shrinkage at 90s than the groups cured by conventional curing and soft start curing (p < 0.05). 4. The initial shrinkage ratios of soft start and exponential curing were statistically lower than conventional curing (p < 0.05). From this study, the use of low initial light intensities may reduce the polymerization rate and, as a result, reduce the stress of polymerization shrinkage.

• 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.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.

• Journal of the korean academy of Pediatric Dentistry
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• v.36 no.1
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• pp.20-29
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• 2009

This study was performed to evaluate the effect of the shrinkage stress induced by polymerization process of several light curing filling materials according to filling methods. High power light curing unit which has a plasma arc lamp was used and filling materials used were Filtek $Z-250^{(R)}$ composite resin, $Dyract^{(R)}$ AP compomer and $Tetric^{(R)}$ Flow flowable composite resin. Cavities were prepared on the permanent molars with width 3 mm, height 3 mm and depth 1.5 mm and the filling materials were filled with 1 step, 2 step layering technique and 3 step oblique filling methods. The results can be summarized as follows; 1. Strain values showed rapid increase from the start of light curing followed by gradual decrease afterwards with time. 2. Although the shrinkage stress value of $Z-250^{(R)}$ were shown to be relatively higher than $Dyract^{(R)}$ AP and $Tetric^{(R)}$ Flow, no statistically significant could be found between tested materials(p>0.05). 3. There were no statistically significant difference between 3 filling methods when using $Dyract^{(R)}$ AP and $Z-250^{(R)}$(p>0.05). 4. There were no statistically significant difference between shrinkage stress values obtained from samples prepared by different filling methods and materials(p>0.05).

• Journal of the korean academy of Pediatric Dentistry
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• v.32 no.2
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• pp.332-343
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• 2005

The purpose of this study was to evaluate the influence of soft-start light curing on contraction stress and hardness of composite resin. Composite resin mold was cured using the one-step continuous curing method with three difference light sources; conventional halogen light curing for 40 seconds at $400\;mw/cm^2$, plasma arc light curing for 6 seconds at $1300\;mW/cm^2$ and LED light curing for 10 seconds at $7The purpose of this study was to evaluate the influence of soft-start light curing on contraction stress and hardness of composite resin. Composite resin mold was cured using the one-step continuous curing method with three difference light sources; conventional halogen light curing for 40 seconds at . For the soft-start curing method ; 2 seconds light exposure at $650\;mW/cm^2$ followed by 3 seconds at $1300\;mW/cm^2$ and exponential increase with 5 seconds followed by 10 seconds at $700\;mW/cm^2$ were used. Contraction stress was measured using strain gauge method and Vickers hardness was measured 24 hours after polymerization at the top and bottom of specimens. Resin-acrylic interfaces were observed using a scanning electron microscope(SEM). The results of present study can be summarized as follows: 1. Contraction stresses at 10 min after polymerization were significantly reduced with the soft-start curing both in plasma and LED light sources(P<0.05). 2. Plasma light curing with soft-start resulted in not only the lowest contraction stress, but also the lowest hardness(P<0.05) 3. LED light curing with soft-start showed lower contraction stress than the one-step continuous halogen and LED light curing(P<0.05). 4. Microhardness of specimens cured by LED light with soft-start was equivalent to that of cured by the one-step continuous halogen and LED light(P>0.05). 5. Curing by LED light with soft-start and conventional halogen light resulted in better marginal sealing than plasma light and one-step LED light curing.

• 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.

• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.2
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• pp.221-232
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• 2006

The purpose of this study was to investigate the effect of step-curing mode on polymerization shrinkage and contraction of composite resin restoration. Class I cavities were prepared on the extracted human premolars. The cavities were ailed with Filtek $Z-250^{TM}$ (hybrid resin, 3M ESPE, USA) and Filtek $flow^{TM}$ (flowable resin, 3M ESPE, USA) and cured with one of the following irradiation modes; Halogen 40sec with continuous curing, LED 10sec with continuous curing, and LED 13sec with step-curing. Contraction stress was measured with strain gauge which was connected to TML $Datalogger^{TM}$ (TDS-102, SOKKI, Japan) and resin-dentin interfaces were observed by scanning electron microscope. The results of present study can be summarized as follows : 1. Composite resin restoration showed transient expansion just after irradiation of curing light. Contraction stress was increased rapidly at the early phase of polymerization and reduced slowly as time elapsed (P<0.05) 2. $Filtek\;flow^{TM}$ showed lower contraction stress than Filtek $Z-250^{TM}$ regardless of curing modes. 3. LED step-curing mode showed lowest contraction stress in Filtek $Z-250^{TM}$ compared with other curing modes(P<0.05). 4. LED step-curing mode showed lowest contraction stress in $Filtek\;flow^{TM}$ compared with other curing modes(P<0.05), but difference in contraction stress was not so greate as in $Filtek\;Z-250^{TM}$. 5. Polymerization of composite resin by LED light with step-curing mode and halogen light with continuous ode resulted in better marginal sealing than LED light with continuous mode.

• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.4
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• pp.606-614
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• 2006

The purpose of this study was to evaluate the polymerization contraction of composite resin(Tetric $ceram^{(R)}$, Ivoclar Vivadent Liechtenstein) according to various liners(Tetric $flow^{(R)}$, Ivoclar Vivadent, Liechtenstein/$Ionosit^{(R)}$, DMG, German/ $Vitrebond,^{TM}$ 3M-ESPE, USA). The strain gauge method was used for measurement of polymerization shrinkage strain. Specimens were divided by 8 groups according to curing units and liners. Group A, E: Tetric $ceram^{(R)}$ bulk filing, Group B, F: Tetric $flow^{(R)}$ lining, Tetric $ceram^{(R)}$ filling, Group C, G: $Ionosit^{(R)}$ lining, Tetric $ceram^{(R)}$ filling, Group D, H: $Vitrebond^{TM}$ lining, Tetric $ceram^{(R)}$ filling. Group A, B, C and D were cured using the conventional halogen light($XL3000^{TM}$ 3M ESPE, USA) for 40 seconds at $400mW/cm^2$. Group E, F G and H were cured using light emitted diode(LED) light(Elipar Freelight $2^{TM}$, 3M-ESPE, USA) for 15 seconds at 800 $mW/cm^2$. Strain gauge attached to each sample was connected to a strainmeter. Measurements were recorded at each second for the total of 750 seconds including the periods of light application. Obtained data were analyzed statistically using Repeated measures ANOVA and Tukey test. The results of this were as follows : 1. Contraction stresses in flowable resin and glass ionomer lining group were lower than that in compomer lining group(p<0.05). 2, Contraction stresses in LED curing light groups were higher than that in halogen curing light groups, but there was no significant difference (p>0.05).

• 대한치과보철학회:학술대회논문집
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• 1997.11a
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• pp.62-62
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• 1997

• Restorative Dentistry and Endodontics
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• v.36 no.3
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• pp.188-195
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• 2011

Objectives: The purpose of this study was to evaluate the polymerization shrinkage stress among conventional methacrylate-based composite resins and a silorane-based composite resin. Materials and Methods: The strain gauge method was used for the determination of polymerization shrinkage strain. Specimens were divided by 3 groups according to various composite materials. Filtek Z-250 (3M ESPE) and Filtek P-60 (3M ESPE) were used as a conventional methacrylate-based composites and Filtek P-90 (3M ESPE) was used as a silorane-based composites. Measurements were recorded at each 1 second for the total of 800 seconds including the periods of light application. The results of polymerization shrinkage stress were statistically analyzed using One way ANOVA and Tukey test (p = 0.05). Results: The polymerization shrinkage stress of a silorane-based composite resin was lower than those of conventional methacrylate-based composite resins (p < 0.05). The shrinkage stress between methacrylate-based composite resin groups did not show significant difference (p > 0.05). Conclusions: Within the limitation of this study, silorane-based composites showed lower polymerization shrinkage stress than methacrylate-based composites. We need to investigate more into polymerization shrinkage stress with regard to elastic modulus of silorane-based composites for the precise result.