Influência de diferentes unidades fotopolimerizadoras no grau de conversão e microdureza de uma resina composta bulk-fill

Abstract

Bulk-fill composite resins have gained popularity in restorative dentistry due to their promise of simplifying clinical procedures by allowing single-increment placement of up to 4-5 mm. However, the effectiveness of polymerization at these thicknesses fundamentally depends on the material characteristics and the light-curing unit employed. This study aimed to evaluate the Knoop microhardness and degree of conversion of Aura Bulk Fill composite resin (SDI) when light cured with two LED devices of different generations: Radii Cal CX (SDI) and Bluephase G4 (Ivoclar Vivadent). Ten cylindrical specimens (5 mm diameter × 4 mm height) and randomly divided into two groups (n=5): Radii Group (light-cured with Radii Cal CX for 20 seconds) and Bluephase Group (light-cured with Bluephase G4 for 20 seconds). Knoop microhardness was measured on the top and bottom surfaces of the specimens using a microhardness tester with a 100 g load for 30 seconds. Data were subjected to two-way analysis of variance (ANOVA) followed by Tukey's post-hoc test (α=0.05). Results demonstrated that depth factor had a statistically significant effect on microhardness (p<0.001), with the top surface showing higher values (Radii: 49.5±6.8 KHN; Bluephase: 51.6±7.7 KHN) compared to the bottom surface (Radii: 37.3±6.6 KHN; Bluephase: 29.0±8.9 KHN). The type of light curing unit showed no significant effect (p=0.376), as did the interaction between factors (p=0.144). The bottom/top ratio was 75.3% for Radii Group and 56.2% for Bluephase Group, indicating that neither group met the minimum criterion of 80% considered adequate by the literature. It is concluded that Aura Bulk Fill resin presented a polymerization gradient in depth, and that the Radii Cal CX device provided better cure homogeneity throughout the 4 mm, although without statistical difference. Complementary studies evaluating the degree of conversion by spectroscopy are necessary to corroborate these preliminary findings.