Effect of different photoactivation techniques on the bond strength of a dental composite

Using the push-out test, this study evaluated the bond strength of the composite resin Z250 (3M/ESPE) photoactivated with the XL2500 (3M/ESPE) quartz-tungsten-halogen light-curing unit with different curing protocols: soft-start (150 mW/cm2 for 2 s (S2), 3 s (S3), 5 s (S5), 10 s (S10) or 15 s (S15), followed by 700 mW/cm2 for 15 s; pulse-delay (150 mW/cm2 for 2 s (P2), 3 s (P3), 5 s (P5), 10 s (P10) or 15 s (P15), with a 1-min delay, followed by 700 mW/cm2 for 15 s. After storage at 37oC ± 1 for 24 h ± 1, the specimens were ground, polished and subjected to a push-out test in a universal test machine (Instron) with a cell load of 500 N at a crosshead speed of 0.5 mm/min. The data were analyzed statistically by ANOVA and Tukey's test at 5 percent significance level. There were no statistically significant differences (p>0.05) among the groups photoactivated using the soft-start mode. For the pulse-delay mode, P5 promoted the highest bond strength (p<0.05). Groups photoactivated with the pulse-delay mode (except for P2 and P15) presented significantly higher bond strength than those photoactivated with the soft-start. It may be concluded that the influence of initial exposure time was curing method-dependent, with the best results obtained using the pulse-delay method with 5 s in the first photoactivation cycle.

O objetivo deste estudo foi avaliar a resistência de união (push-out) da resina composta Filtek Z250 (3M/ESPE), fotoativada com luz de lâmpada halógena XL2500 (3M/ESPE), utilizando diferentes protocolos de fotoativação: soft-start (150 mW/cm2 por 2 (S2), 3 (S3), 5 (S5), 10 (S10) ou 15 s (S15), seguido por 700 mW/cm2 por 15 s; e pulse-delay (150 mW/cm2 por 2 (P2), 3 (P3), 5 (P5), 10 (P10) ou 15 s (P15), com 1 min de espera, seguido de 700 mW/cm2 por 15 s. As amostras foram armazenadas a 37°C ± 1 por 24 h ± 1, lixadas, polidas e submetidas ao ensaio de resistência de união (push-out) em máquina de ensaio universal (Instron) com velocidade de 0,5 mm/min. Os dados foram submetidos à Análise de Variância e teste de Tukey (5 por cento). Os resultados mostraram que não houve diferença significativa entre os grupos fotoativados pelo método soft-start (p>0,05). Para o método pulse-delay, o grupo P5 apresentou a maior resistência de união, significativamente superior aos outros grupos. Os grupos fotoativados pelo método pulse-delay (exceto P2 e P15) apresentaram resistência de união significativamente superior ao método soft-start. Pode-se concluir que a influência do tempo de exposição inicial foi método-dependente, sendo os melhores resultados apresentados pelo método pulse-delay fotoativado com exposição inicial de 5 s.

The effect of different curing modes on composite resin/dentin bond strength in class icavities / 대한치과보존학회지

The purpose of this study was to compare the microtensile bond strength in Class I cavities associated with different light curing modes of same light energy density. Occlusal enamel was removed to expose a flat dentin surface and twenty box-shaped Class I cavities were prepared in dentin. Single Bond (3M Dental product) was applied and Z 250 was inserted using bulk technique. The composite was light-cured using one of four techniques; pulse delay (PD group), soft-start (SS group), pulse cure (PC group) and standard continuous cure (CC group). The light-curing unit capable of adjusting time and intensity (VIP, Bisco Dental product) was selected and the light energy density for all curing modes was fixed at 16 J/cm2. After storage for 24 hours, specimens were sectioned into beams with a rectangular cross-sectional area of approximately 1 mm2. Microtensile bond strength (microTBS) test was performed using a universal testing machine (EZ Test, Shimadzu Co.). The results were analyzed using oneway ANOVA and Tukey's test at significance level 0.05. The microTBS of PD group and SS group was higher than that of PC group and CC group. Within the limitations of this in vitro study, modification of curing modes such as pulse delay and soft start polymerization can improve resin/dentin bond strength in Class I cavities by controlling polymerization velocity of composite resin.

Effect of different modes of light modulation on the bond strength and knoop hardness of a dental composite

This study evaluated the bond strength and Knoop hardness of Z250 composite resin, light activated with XL2500 curing unit, using different protocols: continuous mode - high intensity (CH) (700 mW/cm²) for 20 s; continuous mode - low intensity (CL) (150 mW/cm²) for 20 s; and pulse-delay with 150 mW/cm² for 2(P2), 3(P3), 5(P5), 10(P10) or 15 s (P15), with a 1-min delay, followed by 700 mW/cm² for 20 s. For the push-out test (n=10), the bond strength values were obtained using a universal test machine at a crosshead speed of 0.5 mm/min. For Knoop hardness (n=5), the specimens were made using the same light-activation protocols. The hardness measurements were made with a hardness tester at six depths (top, 1, 2, 3, 4, and 5 mm). The data were subjected to ANOVA and Tukey's test at 5 percent significance level. For bond strength, CL and P5 presented significantly higher mean values (p<0.05) than the other groups. There was no statistically significant difference (p>0.05) between P2, P3, P10, P15 and CH. For Knoop hardness, CH and P15 presented the highest mean values from top surface up to 4 mm depth , while CL presented the lowest hardness mean values (p<0.05). From the depth of 3 mm to 5 mm, the mean values of all groups were significantly lower (p<0.05) than those recorded on top surface. In conclusion, for the pulse-delay method, the initial exposure time can influence bond strength and Knoop hardness of composites.

Este estudo verificou a resistência de união e a dureza Knoop do compósito Z250 (3M/ESPE), fotoativado com luz de lâmpada halógena (XL2500, 3M/ESPE), utilizando diferentes protocolos: modo contínuo alta intensidade (CH) (700mW/cm²) por 20s; modo contínuo baixa intensidade (CL) (150mW/cm²) por 20s; pulse-delay com 150mW/cm² por 2(P2), 3(P3), 5(P5), 10(P10) ou 15(P15) segundos, com 1 min de espera, seguido por 700mW/cm² por 20s. Para o teste de união push-out (n=10), os valores de resistência de união foram obtidos em máquina de ensaio universal Instron. Para o ensaio de dureza Knoop (n=5) os espécimes foram fotoativados pelos mesmos protocolos utilizados no ensaio de resistência de união. As medidas de dureza foram realizadas em um microdurômetro (Shimadzu) em 6 profundidades (topo, 1, 2, 3, 4 e 5 mm). Os dados foram submetidos à Análise de Variância e ao teste de Tukey com nível de significância de 5 por cento. Os resultados mostraram que P5 e CL apresentaram resistência de união estatisticamente superior a todos os grupos. Não houve diferença entre os grupos P2, P3, P10, P15 e CH. Para dureza Knoop, CH apresentou os maiores valores, estatisticamente superiores a P2 e CL até 4 mm. A partir de 3 mm, a dureza de todos os grupos foi inferior a dureza do topo. O tempo de exposição inicial para o modo pulse-delay pode influenciar a resistência de união e a dureza Knoop.