Influência dos aparelhos fotopolimerizadores na transmissão da luz e na microdureza de resinas compostas bulk-fill de polimerização rápida em restaurações classe II

Abstract

Aim: To evaluate the effect of different light-curing units on Class II restorations of bulk-fill resin composites using fast and conventional polymerization protocols. Materials and Methods: Two multiwave LED light-curing units (Bluephase PowerCure – Ivoclar Vivadent, Schaan, Liechtenstein; Quazar – FGM, Joinville, SC, Brazil) were used to polymerize the tested materials under two modes: 3s (high irradiance, short exposure time) and 20s (standard irradiance and standard exposure time). The devices were characterized based on radiant power (mW), tip internal diameter (mm), tip irradiance (mW/cm²), emission spectrum (mW/cm²/nm), and irradiance profile (mW/cm²). The emission spectrum was evaluated through the materials at depths of 1, 3, and 4mm using a spectrometer coupled to an integrating sphere. Irradiance profiles were obtained using a beam profiler and analyzed at the same depths. Class II MOD restorations (3×6×4mm) were performed in typodont premolars (Oclusal – Oclusal Produtos Odontológicos Ltda, São Paulo, SP, Brazil) using four bulk-fill composites: two low-viscosity (Tetric N-Flow Bulk Fill and Tetric PowerFlow – Ivoclar Vivadent, Schaan, Liechtenstein) and two high-viscosity (Tetric N-Ceram Bulk Fill and Tetric PowerFill – Ivoclar Vivadent, Schaan, Liechtenstein) materials. Two restorative techniques were used: low-viscosity bulk-fill + high-viscosity bulk-fill, or high-viscosity bulk-fill. The fast-curing resins (Tetric PowerFill and Tetric PowerFlow) were polymerized using the 3s mode, whereas the conventional resins (Tetric N-Flow and Tetric N-Ceram) were cured using the 20s mode. Regional polymerization depth was assessed using Knoop microhardness at 0.5, 1, 2, 3, and 4mm depths in the mesial, central, and distal regions. Radiant power, tip diameter, tip irradiance, emission spectrum, and irradiance profiles were descriptively analyzed. Regional depth data were tested for normality (Shapiro-Wilk) and homogeneity of variance (Levene). Repeated-measures ANOVA followed by Tukey’s post-hoc test was used (α=5%). Results: Irradiance values were similar between devices. Higher results were observed in the 3s mode. Radiant exposure increased with longer exposure time. Light transmission decreased with increasing resin thickness. Regarding regional polymerization depth, statistically significant differences were found for depth (p<0.001) and resin type (p<0.001), but not for region (p=0.283) or light-curing unit (p=0.174). Microhardness decreased as depth increased. Low-viscosity resins showed lower microhardness values. Conclusion: Light transmission and polymerization depth decreased as resin thickness increased. High irradiance with short exposure time produced regional microhardness values comparable to those achieved with standard irradiance and standard exposure time, regardless of the light-curing unit used.