Avaliação da resistência à flexão de resinas compostas após diferentes técnicas de polimerização

Abstract

The aim of this study was to evaluate the influence of complementary microwave polymerization on the flexural strength of two first light-cured direct restorative composites. For this purpose, 120 specimens were produced with a size of 25mm long x 2mm wide x 2mm high with Z350 (3M®) and FORMA (Ultradent®) resins. The photopolymerization was carried out for 60 seconds at the power of 1000mw/cm² (three different points of 20 seconds) in certain groups, and for 9 seconds at the maximum power of 3200mw/cm² (three different points of 3 seconds) in other groups. After that, the samples were placed in a microwave for 3 minutes at the maximum power (MEF41, 1000 mW, Electrolux, Stockholm, Sweden), one group with the specimens submerged in water and the other not. Two control groups were established, which consisted of using Z350 (3M®) and FORMA (Ultradent®) resins conventionally light-cured at the power of 1000mw/cm². Flexural strength testing was performed on the Universal Testing Machine (EMIC, model DL 20000, São José dos Pinhais, PR, Brazil) where a device was adapted for the specific test. The results were subjected to analysis of variance (ANOVA) with two factors (resin and treatment). Resin variable in two levels, Z350 (3M®) and FORMA (Ultradent®), and polymerization treatment in 6 levels (1000mW, 3200mW, dry microwave + photo 1000 mW, dry microwave + photo 3200 mW, wet microwaves + photo 1000 mW and wet microwave + photo 3200 mW). The results showed that there was a statistically significant difference (p = 0.0307) in the comparison between groups G1 (photopolymerization for 60s, with power of 1,000mW/cm²) and G7 (photopolymerization for 9s, with power of 3,200mW/cm²), in which the Z350 resin was used showing greater effectiveness when using higher power in less activation time, and also showed a statistically significant difference between G1 and G2, with p = 0.047, demonstrating that the use of post-cure polymerization for 3 minutes in microwaves using high power was able to generate an increase in the flexural strength of the Z350 resin.