The performance of adhesive resin materials has been markedly improved and their clinical application is expanding. Even when excellent adhesive resin materials are used in clinics, gap formation in cavity floors and walls is caused by polymerization shrinkage of composite resin. To prevent gap formation in clinical situations, many kinds of research have been conducted. Dentin-bonding performance of recent adhesive resins has markedly improved；however, bonding to caries-affected dentin was known to be weaker compared with bonding to intact dentin. New bonding procedures to caries-affected dentin were developed, and its bonding was improved. Enamel bonding was re-evaluated, and a reliable method of bonding with less invasive surface treatment was also established. A clinical procedure to effectively prevent gap formation in a cavity restored with light-cured composite resin was established and clinically applied. A new application of adhesive resin materials to prevent coronal leakage, which is considered to affect the clinical longevity of restorations applied to non-vital teeth, was also developed. These studies were supported by the development of evaluation methods for bond strength and cavity sealing, such as the new bond test methods and optical coherent tomography.

This study investigated the wear behavior of similar CAD/CAM restorative materials by the two-body wear test in vitro. Zirconia (ZR), lithium disilicate glass-ceramics (LS), and resin composite (RC) were used to fabricate crown-shaped abrader and plate-shaped substrate specimens. After fixing specimens to the abrasion tester, two-body wear tests were performed under water immersion at room temperature using the following parameters：an applied load of 4.9 N, stroke width of 5 mm, and stroke cycle of 30,000 cycles (n＝6). The worn surfaces of the specimens were evaluated using a contour-measuring instrument, a 3D laser microscope, and a scanning electron microscope. The amounts of wear in both abrader and substrate specimens showed the lowest values for ZR, which is devoid of a glass phase, followed by RC and LS. The wear facets on the abrader specimens were clear on RC and LS, which contain glass filler or matrix. The maximum worn width and worn depth of the substrate specimen were the largest for LS. These results indicate that the differences in the composition and structure of the materials used affect the wear behavior of similar materials and should be taken into consideration while selecting materials for clinical application.