RESUMEN
The aim of this study was to evaluate the polymerization stress and degree of conversion of a composite submitted to different photoactivation protocols. The composite Filtek Z350 was placed in the central perforation of a photoelastic disc and polymerized using a LED-based curing unit (BluePhase II--Ivoclar Vivadent) with energy density of 12, 24 or 36 J/cm2 using the following photopolymerization protocols: continuous high intensity (HI: 1200 mW/cm2 during 10, 20 or 30s), continuous low intensity (LI: 650 mW/cmz during 18, 36 or 54s) and soft-start (SS: 150 mW/cm2 during 5 s + 1200 mW/cm2 during 9, 19 or 29s) (n = 5). Photoelastic analysis was used to evaluate polymerization shrinkage stress and FTIR was performed to determine the degree of conversion of the composite. ANOVA 3-way procedure was used to determine the significance of the main effects and their interactions followed by two-way ANOVA for each time was performed (p < 0.05). Shrinkage stress increased with higher values of energy. No statistically significant differences on polymerization shrinkage stress were found between high and low intensity activation modes. Soft-start method generated stresses that were statistically lower than continuous modes except when 12 J/cm2 was applied. Similar degree of conversion was observed for photoactivation modes used, except for soft-start mode with 12, 24 and 36J/cm2 that showed lowest levels of conversion. Energy density and activation mode influenced polymerization shrinkage stress, but no benefit on degree of conversion was observed.
Asunto(s)
Resinas Compuestas , Análisis del Estrés Dental , Luz , Ensayo de Materiales , PolimerizacionRESUMEN
The aim of this study was to evaluate the polymerization stress and degree of conversion of a composite submitted to different photoactivation protocols. The composite Filtek Z350 was placed in the central perforation of a photoelastic disc and polymerized using a LED-based curing unit (BluePhase II - IvoclarVivadent) with energy density of 12, 24 or 36 J/cm² using the following photopolymerization protocols: continuous high intensity (HI: 1200 mW/cm² during 10, 20 or 30s), continuous low intensity (LI: 650 mW/cm² during 18, 36 or 54s) and soft-start (SS: 150 mW/cm² during 5 s + 1200 mW/cm² during 9, 19 or 29s) (n=5). Photoelastic analysis was used to evaluate polymerization shrinkage stress and FTIR was performed to determine the degree of conversion of the composite. ANOVA 3-way procedure was used to determine the significance of the main effects and their interactions followed by two-way ANOVA for each time was performed (p<0.05). Shrinkage stress increased with higher values of energy. No statistically significant differences on polymerization shrinkage stress were found between high and low intensity activation modes. Softstart method generated stresses that were statistically lower than continuous modes except when 12 J/cm² was applied. Similar degree of conversion was observed for photoactivation modes used, except for soft-start mode with 12, 24 and 36 J/cm² that showed lowest levels of conversion. Energy density and activation mode influenced polymerization shrinkage stress, but no benefit on degree of conversion was observed.
O objetivo neste estudo foi avaliar a tensão de contração de polimerização e o grau de conversão de uma resina composta submetida a vários protocolos de fotoativação. O compósito Filtek Z350 foi inserido na perfuração central de um disco de resina fotoelástica e polimerizado usando uma unidade de fotoativação LED (BluePhase II - IvoclarVivadent) com as doses de energia de 12, 24 or 36 J/cm² usando os seguintes protocolos de polimerização: contínuo de alta intensidade (HI: 1200 mW/cm² durante 10, 20 ou 30s), contínuo de baixa intensidade (LI: 650 mW/cm² durante 18, 36 ou54s) e "soft-start" (SS: 150 mW/cm² durante 5 s + 1200 mW/cm² durante 9, 19 ou 29s) (n=5). Análise fotoelástica e Espectroscopia Infravermelha Transformada de Fourier (FTIR) foram usados para avaliar a tensão de contração de polimerização e grau de conversão do compósito respectivamente. O teste ANOVA três fatores foi usado para determinar os principais efeitos e interações das variáveis e seguidamente, ANOVA 2 fatores para ver a diferença entre os grupos (p<0.05). A tensão de contração aumentou com valores maiores de energia. Não foram observadas diferenças estatisticamente significantes para a tensão de contração entre os modos de alta e baixa intensidade. O modo "soft-start" gerou menor tensão que os modos contínuos, exceto quando 12 J/cm² foi aplicado. Similar grau de conversão foi observado para os modos de fotoativação usados, com exceção do modo "soft-start" com 12, 24 e 36 J/cm² que mostraram níveis menores de conversão. A dose de energia e modo de ativação influenciam a tensão de contração de polimerização, porém nenhum benefício no grau de conversão foi observado.