Enhancing photopolymerization and modeling kinetic degradation in dental composites

This study aims to optimize the photopolymerization process of a dental composite in order to increase the degree of conversion and reduce the release of unpolymerized monomers. In addition, it seeks to understand the kinetics of composite degradation under various oral environmental conditions. Optimization of the photopolymerization process is carried out using a Box-Behnken design, exploring factors such as irradiation time, intensity and distance. Infrared spectroscopy is used to evaluate photopolymerization parameters. Release of unpolymerized monomers is quantified using liquid chromatography at different pH levels, incubation media and time. Thermogravimetric analysis is used to study thermal degradation and establish a kinetic model. Optimized conditions for photopolymerization, determined as an irradiation time of 40 s, an intensity of 1500 mW cm⁻², and a distance of 5 mm, lead to a degree of conversion of 61%, reducing the presence of unpolymerized monomers. Chromatographic analysis reveals a pH-dependent release of monomers, with acid saliva showing the highest release. Thermal analysis indicates variable activation energy values depending on ageing conditions, underlining the importance of optimal conversion for increased material strength. This study offers a comprehensive approach to improving the properties of dental resins, and provides optimized conditions for light-curing that increase material strength.