The purpose of the present study was to analyze effective factors including periodontal ligament on vertical root fractures (VRFs) . Eighty maxillary central incisors were assigned to eight groups, depending on master apical file (MAF) size, loading point and existence of a simulated periodontal ligament (PDL) . The gutta-percha in the root canal was vertically pressed with a Co-Cr rod using a universal testing machine. An ordinal logistic analysis was employed to determine significant factors. VRFs were observed in 88.8% of the specimens but no horizontal fractures were found. There were three types of VRFs: partial fracture not involving the apex (PF, 41.3% ) , partial fracture involving the apex (AF, 40.0% ) , and complete fracture (CF, 7.5% ) . MAF size significantly affected VRFs (p< 0.05) ; large MAF size exhibited more partial fractures involving the apex. Loading point and existence of PDL did not affect VRFs.

The purpose of the present study was to evaluate how ultraviolet light (UV) irradiation using an ordinary UV sterilizer would affect the bonding of experimental composite resins to an autopolymerizing acrylic resin. To this end, three composite resins and one unfilled resin -of which the compositions were similar to commercial composite resin artificial teeth -were prepared as repair composites. Their shear bond strengths after UV irradiation for one to 60 minutes were significantly greater than those before UV irradiation regardless of composite resin type. Failure mode after UV irradiation for one to 60 minutes was mainly cohesive failure of the composite resins, but that before UV irradiation and after 24 hours' irradiation was mainly adhesive failure. These results thus suggested that a short period of UV irradiation on composite resin teeth would improve the bonding efficacy of composite resin artificial teeth to autopolymerizing resin.

The morphological assessment of wear tracks refects the nature of the abrasive and reveals insight into the mechanism generating wear patterns. Morphological details confirmed abrasive and fatigue-related wear as main failure mechanisms. Selection of food-like slurries as third-body media, such as poppy seed suspension is mandatory to simulate wear of composite restorations in occlusal cavities where three-body wear is the dominating determinant of loss of substance and surface deterioration.