Photocured dental restorative materials: Effect of exposure time on curing, glass transition, modulus and water sorption

Abstract

Two species of photocured dental restorative materials commercially available (Dimefill TL and Silux Plus) were employed to study the effect of exposure time and sample storage on the matrix polymerization, glass transition temperature, flexural modulus, water uptake and extractable fraction. The methods used for thermal analysis were differential scanning calorimetry and dynamic mechanical thermal analysis. The photoinitiator systems are decomposed within 40 or 20 s of illumination with visible violet light. The conversion is proportional to the logarithm of exposure time within the range 5–160 s. However, the conversion remains rather incomplete even after prolonged photocuring (160 s), as evidenced by low values of the glass transition temperature T g and flexural modulus E(37 °C). During the storage of photocured samples some progress of polymerization takes place, which is manifested by a perceptible increase in both T g and E(37 °C). An extensive additional polymerization attributed to living radicals can be observed at elevated temperatures (60–80 °C) if the post-curing is performed shortly after the illumination. Water uptake and extractable fraction diminish with the time of curing as the network density increases.