Influence of curing-light beam profile non-uniformity on degree of conversion and micro-flexural strength of resin-matrix composite

Abstract

Background. Beam profile non-uniformity of light-curing units (LCUs) may result in suboptimal properties of resin-matrix composite (RMC) restorations. Objectives: The objective of this study was to evaluate the effect of curing-light beam profile of multiple light curing units (LCUs) on the degree of conversion (DC) and micro-flexural strength (μ-flexural strength) of RMC. Methods: Forty-five nano-filled hybrid RMC (Tetric EvoCeram, Ivoclar Vivadent, Amherst, NY) specimens were fabricated. Quartz tungsten halogen (QTH) (Optilux 401) (O), multiple emission peak (VALO Cordless) (V) and single emission peak (Demi Ultra) (DU) light-emitting-diode (LED) LCUs were investigated at different light-curing locations (LCLs): 1) the center of the LCU tip; 2) 1.5 mm to the left of the center of the LCU tip; and 3) 1.5 mm to the right of the center of the LCU tip. Specimens were stored wet in deionized water at 37C for 24 hours. The DC was measured on top and bottom surfaces using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy. Micro-flexural strength testing was performed using a universal mechanical testing machine at crosshead speed of 1 mm/min. Multi-factorial ANOVAs were used to analyze the data (α = 0.05). Results: All LCUs exhibited significant differences in DC between top and bottom surfaces at the different LCLs. Micro-flexural strength varied with LCL for DU. Conclusions: The non-uniform curing-light beam profile could have a significant effect on μ-flexural strength and DC on top and bottom surfaces of RMC specimens cured at different LCLs.