Relación de la energía de polimerización y Degradación por UV, sobre el grado de conversión en composites

Abstract

The degree of conversion (DC) is directly related with the physical and mechanical properties that allow a successful restorative treatment. The aim of this study was to evaluate the influence of the energy density, on the DC in composites, as a function of the subjected time to accelerated aging by UV. Two hundred and forty resin composite specimens were made, using a stainless steel mold of 6mm - diameter x 2mm - depth; the energy output was applied, only, over the top area of the samples. The materials used were: Filtek Z-250 - Filtek Supreme / 3M ESPE and Tetric Ceram - Tetric EvoCeram / Ivoclar Vivadent. The specimens were divided in three groups (according the energy output): A (3.75 J/cm2 ), B (9 J/cm2 ) and C (24 J/cm2 ), and each one of them, subdivided in: 1(no aging), 2 (500 hours of aging), 3 (1000 hours of aging) and 4 (1500 hours of aging). The results were analyzed by means of ANOVA and Tukey tests (p<0.05) to determine the effect of the factors. Correlation and lineal regression were performed to determine the possible relationship among the variables. The energy density determined the DC in specimens without aging; however, it is not a decisive factor after 500 h under accelerated aging by UV. The DC increases significantly, while the time of aging increases: 0 h (53.9%), 500 h (62.7%), 1000 h (77.5%), but after 1500 h, the material presents a significant decrease of DC (61.4%). The organic matrix degradation and the generation of double bonds, after 1500 h under accelerated aging is, probably, the cause for the decrease of DC. The clinician, should keep this behavior in mind, to check the composite restorations frequently.