Diferença entre o grau de conversão de polimerização e microdureza de resinas compostas de diferentes cores

Abstract

Light-cured composite resins are essential materials in restorative dentistry, standing out for their clinical versatility, adequate mechanical strength, good handling properties, and satisfactory esthetics, which are provided by the wide range of available shades and opacities. The effectiveness of these materials depends significantly on proper polymerization. The degree of conversion and microhardness are critical mechanical properties that determine the clinical performance of restorations. This study investigated whether there is a statistically significant difference in the degree of polymerization conversion and microhardness of composite resins with different shades (B1 and A3.5), light-cured using the same photoinitiator under identical conditions of power, light intensity, and activation time. This experimental comparative study included five specimens for each composite resin shade. The specimens were standardized with dimensions of 5 mm in diameter and 2 mm in thickness, molded using a silicone matrix to form uniform cylindrical samples. Light curing was performed using a Bluephase G4 LED curing unit (Ivoclar Vivadent) for 20 seconds, applying a light intensity of 1200 mW/cm2. After polymerization, the specimens were sequentially polished using abrasive papers of different grit sizes and analyzed by Fourier-transform infrared spectroscopy (FTIR) to determine the degree of conversion, as well as by the Knoop microhardness test. The data were statistically analyzed using the independent Student’s t test, with the level of significance set at P < 0.05. The results showed that both groups exhibited high degrees of conversion (B1: 80.90% ± 7.32% and A3.5: 82.46% ± 10.24%), with no statistically significant difference between them (p = 0.789). Similarly, microhardness values (B1: 119.3 ± 5.35 HK and A3.5: 112.2 ± 15.55 HK) did not differ significantly between the groups (p = 0.365). These findings indicate that the shade of the composite resin, within the evaluated tonalities, does not significantly influence either the degree of conversion or microhardness when subjected to the same light-curing conditions. Therefore, the mechanical performance of composite resins with different shades does not present clinically relevant variations, allowing clinicians to prioritize esthetic criteria when selecting the shade without compromising the mechanical properties of the restoration.