Effects of extended curing time on the diametral tensile strength, degree of conversion, and monomer release of bulk-fill composite resins

Abstract

This study aims to evaluate the effects of extended curing of bulk-fill composite resins with a light-emitting diode (LED) by investigating the diametral tensile strength (DTS), degree of conversion (%DC), and bis-GMA monomer release (MR). A total of 144 specimens (diameter, 5 mm and thickness, 4 mm) with three different bulk-fill composite resins were investigated by divided them into three groups with curing times of 20, 25, and 30 s, with LED irradiance of 900 mW/cm2. After 24 h of curing, each specimen was analyzed using a universal testing machine, Fourier-transform infrared (FTIR) spectroscopy, and high-performance liquid chromatography (HPLC) to determine the DTS, %DC, and bis-GMA MR, respectively. The data were analyzed using a one-way ANOVA (α = 0.05). It was observed that DTS increased as the curing time increased for all resins tested but only the differences in the FBF samples were statistically significant. The %DC was in the range 45.92%–74.65% but was not affected by curing time (P ≥ 0.05). FBF exhibited the lowest MR of all the resins. It can be concluded that extending the LED curing time increases the DTS of bulk-fill composite resins but did not affect the %DC or MR.