Evaluation of degree of conversion of various composite resin restorative materials polymerized by various light sources using microhardness measurement

The purpose of this study was to evaluate degree of conversion of two different composite resin restorative materials polymerized by using two different light curing units with three different distance and two different light application durations.In this study, 120 extracted human lower third molar teeth were used. Standard class I cavities were prepared and self-etching bonding system was applied to cavities. Two different composite resin restorative materials with A2 color were placed to cavities by bulk technique. Restorative materials were polymerized by using two different light curing units. Light curing units were used on two different irradiation time such as 20 sec and 40 sec with three different distances, 0 cm, 0.5 cm and 1 cm. After restorations, the teeth were divided into two parts by using hard tissue cutting device. Micro hardness measurements were conducted by using micro hardness device (HMV-II, Shimadzu, Japan).Statistical analyses of obtained data were evaluated by ANOVA and Tamhane tests.Following results were observed: for all tested groups, flowable composite showed higher microhardness values then hybrid composite resin. Increase of light use period for light curing units used on the polymerization of composite resin restorative materials provided an increase for microhardness values and monomer conversion degree of material. The increase of distance between light curing units and material surface caused a decrease on the surface microhardness values and monomer conversion degree. LED light curing unit indicated higher microhardness values and monomer conversion degree compared with the QTH light curing unit.