We examined the abrasiveness of glycine powders with particle diameters of 63 and 100 mum by measuring the depth and volume of defects produced during air polishing of human dentin. A total of 36 extracted human teeth were embedded in acrylic resin. The resin blocks were polished until the dentin surfaces were exposed. The nozzle of an air polisher was mounted 4 mm from the dentin surface, and the dentin surface was treated for 5 s at one of two angles of incidence (45 degrees or 90 degrees). Three materials were used in the polishing process: NaHCO(3) powder with a mean particle diameter of 100 microm (Handy Jet Powder), glycine powder with a mean particle diameter of 63 microm (Handy Jet Powder PMTC), and glycine powder with a mean particle diameter of 100 microm (Handy Jet Powder Recall). The defect depth at both angles was significantly deeper after treatment with Handy Jet Powder or Handy Jet Powder PMTC. The defect volume was the greatest with Handy Jet Powder, followed by Handy Jet Powder PMTC, and Handy Jet Powder Recall. The larger diameter glycine powder resulted in less damage to the dentin.

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 ...

To investigate the effects of different fillers and their contents on the wear of composite resins, four composites (CS: non-porous spherical silica, AS: porous spherical silica, AZ: porous spherical zirconium silicate, and IS: non-porous irregular-shaped silica) were experimentally prepared using different fillers (CS, AZ, AS and IS). Simulated occlusal wear and toothbrush wear were evaluated for these composites and their worn surfaces were observed. The mechanical properties (flexural strength, elastic modulus and hardness) of these composites were determined to examine the relationships between wear and these mechanical properties. CS showed the highest occlusal wear, but the lowest toothbrush wear among four composites. AS and AZ had lower occlusal wear than CS and IS, while their toothbrush wear was higher than CS and close to that of IS. All composites showed increase in the occlusal wear as filler content increased. CS and IS showed decrease in the toothbrush wear as the filler content increased, whereas AS and AZ did not. The occlusal wear surfaces of CS and IS had concavities, while those of AZ and AS were relatively smooth with flattened filler. The toothbrush wear surfaces of CS and IS revealed the extrusion of filler from resin matrix, whereas those of AZ and AS were smooth with flattened filler. The toothbrush wear of CS and IS decreased as the mechanical properties increased, whereas those of AS and AZ did not. The occlusal wear of all composites increased as the mechanical properties increased, which would not reflect effects of these mechanical properties.

The aim of this study was to investigate the effect of antagonist material and configuration on combined wear, which was produced by alternating toothbrush wear and simulated occlusal wear on one specimen. Worn volume and maximum worn depth comparisons were done using two antagonist materials (steel and ceramic) and two antagonist configurations (flat and round).For the material factor, worn volume by the ceramic antagonist was greater than that by steel antagonist in the combined wear test. For the configuration factor, the round ceramic antagonist induced a greater volume loss of the resin composite. As for maximum worn depth, both the material and configuration of antagonist were influencing factors in the combined wear test -where the round ceramic antagonist induced a deeper wear of the resin composite. Based on the results of this study, we concluded that a round ceramic antagonist is suitable to be used for evaluating the wear behavior of resin composites.

The aim of this study was to examine defect depths and volumes at the resin composite-dentin (R/D) interface after air polishing with different particles and spray angles. Samples were 54 dentin specimens that were formed in saucer-shaped cavities filled with resin composite. Each specimen was air polished with either sodium bicarbonate (NaHCO3) or one of two glycine (Gly) powders. The air polisher was set at angles of 90° to the interface and at 45° to the interface from both the dentin and resin composite sides. Air polishing with Gly powder produced defects with less depth and volume than NaHCO3 powder (p < 0.05). Air polishing with a spray angle of 45° to the interface from the resin composite side produced fewer defects (p < 0.05) than polishing from the dentin side. Air polishing to the R/D interface from the resin composite side produced fewer defects to the interface because the hardness of the resin composite was higher than that of dentin.