INTRODUCTIONWear of restorative materials is a very complex phenomenon that is affected by several extrinsic and intrinsic factors. Wear of restorative materials in the oral environment results from direct contact between the tooth and the restoration during mastication, oral parafunctions, toothbrushing with abrasive particles, as well as chemical effects caused by dietary and regurgitated acids 1） . To date, many studies 2-9） have attempted to evaluate the wear behavior of restorative materials using several testing methods. However, these methods evaluated only a part of the wear process of restorative materials. It is absolutely necessary to integrate main wear processes such as abrasion and fatigue for a thorough and holistic evaluation of the wear behavior of restorative dental materials. To this end, a combined wear test system -which carried out two different types of wear test -was developed 10） . In the combined wear test, a simulated occlusal wear test and a toothbrush wear test repeated alternately on the same position of one specimen. This testing system provided a means for clinical simulation and a basic wear model which consisted of different wear mechanisms induced in the oral environment. Occlusal force and brushing force are important factors for characterizing the wear behavior of restorative dental materials, especially when the two different wear processes are combined.The purpose of this study was to investigate the effects of different occlusal forces and brushing forces on the wear of composite resins in the combined wear test as well as in the simulated occlusal wear test and toothbrush wear test. Table 1 shows four commercially available light curing composite resins used in this study. APX （KURARAY, Okayama, Japan）and Z100（3M, MN, USA）were intended for both anterior and posterior restorations, while SRE （GC, Tokyo, Japan） and SDX（Shofu, Kyoto, Japan）were for posterior restorations. Preparation of the wear specimens and wear tests were carried out following the procedure reported in a previous study 11） . Wear specimens were prepared using a metal mold （diameter: 15 mm, depth: 8 mm） . Thickness of the specimens was adjusted to 2 mm using a spacer in the mold. Each composite resin was injected into the mold and pressed with a glass plate（1.4 mm thickness） . The specimen was polymerized using a curing light MATERIALS AND METHODS Specimen preparation and wear testEffects of occlusal and brushing forces on the wear of composite resins were investigated using three different wear tests: simulated occlusal wear test, toothbrush wear test, and combined wear test which carried out toothbrush wear test and occlusal wear test alternately. Test specimens were prepared from four commercial composite resins. Worn volume and maximum worn depth were measured under different occlusal forces（40 N and 80 N）and brushing forces（1.5 N and 3 N） in the three wear tests. Worn surfaces were observed using a SEM.In all the three wear tests, both higher occlusal and brushing forces resulted in significantly ...