The Effect of Pre-Heating on Fracture Toughness in Three Distinct Composite Resin Systems at Two Different Temperatures: A Protocol for an In-vitro Study

Introduction: Composite resins are considered the pinnacle of esthetic restorations, but they have their own disadvantages, such as polymerization shrinkage, low fracture toughness, and the formation of microcracks, all of which eventually results in failure of the restoration. Fracture toughness is an important factor for failure. Warming the same composites to certain temperatures will show drastic improvements in the abovementioned flaws, especially the fracture toughness. Need for the study: Therefore, the objective of this study is to evaluate and compare the fracture toughness of three different types of composite resin systems at two different pre-heating temperatures. The study aims to provide valuable information to clinicians in choosing the most appropriate restorative material for posterior composite restorations, which can ultimately improve the treatment's success rate and reduce the risk of complications such as secondary caries, postoperative sensitivity and ultimately restoration failure. Objective: In summary, this study will compare and evaluate the fracture toughness of nanohybrid, micro-hybrid, and bulkfill composite resins pre-heated at 50 degrees Celsius and 60 degrees Celsius. Methodology: The methodology involves dividing 72 freshly extracted premolars with intact occlusal anatomy and fully developed apical foramina into three main groups based on three different composites and further dividing each group into two sub-groups based on two different pre-heating temperatures, with 12 teeth in each group. Each tooth will then be prepared with a Class-II Mesio-Occlusal-Distal (MOD) cavity and receive pre-heated composite restoration according to its assigned group and sub-group. The prepared samples will be tested for fracture toughness using a universal testing machine.