Grau de conversão de resinas compostas.influência do método de fotopolimerização

Objectives: To evaluate the degree of conversion of four composite resins and to determine the influence of two polymerization methods. Methods: Forty 2mm thick composite disks were assigned to 8 experimental groups (n=5) according to several possible combinations between the polymerization methods [QTH curing unit (400mW/cm²)/40s and a LED curing unit (800mW/cm²)/20s] and the composites [Suprafil (R&S), Natural Elegance (Henry Schein Inc.), Proclinic Composite PM (Madespa SA) and FiltekTM Z250 (3M ESPE)] tested. Specimens were polymerized exposing the light only to the top surface. Human enamel was used below the disks, as a reflection material. After dry storage in the dark for 24h, Vickers microhardness measurements were performed for each specimen on the top and bottom surfaces. Microhardness ratio was calculated for each specimen. A minimum of 0.80 was considered as a correct polymerization. Data were analyzed with ANOVA and t-Teste. Results: Microhardness ratio ranged between 0.79 and 0.98. To QTH specimens, Z250 showed statistically (p<0,05) higher ratios than the others composites. To LED specimens, there were no statistically (p=0.05) differences between composites with the exception of Suprafil who has shown a lower ratio. Conclusions: Despite the fact that Z250 showed an higher microhardness ratio, all the experimental groups reached an adequate polymerization, excepted for the group Proclinic/QTH (0.79). Using the LED curing unit may reduce the working time.