Resumo

XAVIER DE LIMA, Anna Letícia et al. Evaluation of the degree of conversion of composite resins photoactivated in different curing times and power densities. RFO UPF [online]. 2016, vol.21, n.2, pp. 219-223. ISSN 1413-4012.

Introduction: Adequate polymerization is a crucial factor in obtaining optimal physical properties and clinical performance of composite resins. Objective: To evaluate the degree of conversion (DC) and hardness of composite resins photoactivated in different power densities and curing times. Materials and method: Eighty (n=80) composite resin specimens (FiltekTM Z350 XT color A2B) with 4 mm of diameter and 2 mm of thickness were produced, whereas forty (n=40) were meant for the evaluation of degree of conversion and forty (n=40) for hardness. Ten (n=10) specimens were produced for each group assessed, whereas five were meant for the evaluation of the degree of conversion and five for hardness (P10T2; P7T2; P4T2; P1T2; P10T4; P7T4; P4T4; P1T4). Resins of the degree of conversion and hardness were photoactivated by LED for 20 seconds at power intensities of 1000 mW/cm2, 700 mW/cm2, 400 mW/cm2, and 100 mW/cm2, for groups P10T2, P7T2, P4T2, and P1T2, respectively. Groups P10T4, P7T4, P4T4, and P1T4 were cured in the same power intensity, but for 40 seconds. Result: Regarding the degree of conversion, P1T2 resins had the lowest mean value of 22.67 %, and P10T4 resins had the highest mean value of 87.9%. As for hardness, P1T2 resins also had the lowest mean of 30.93 kgf/mm², and P10T4 had the highest mean of 82.02 kgf/mm². Conclusion: The higher the power of the curing unit, the higher the DC and hardness of composites resins. The results of this study suggest that a device with intensity of 100 mW/cm² does not provide satisfactory degree of conversion and hardness, compromising the performance of the restorative material.

Palavras-chave : Hardness; Polymerization; Composite resins.