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Resins for crown and bridge have been widely used as veneers on rnetal frames to provide restorations of anterior teeth because the reproducibility of the aesthetics appearances is relative}y easyi-6), The reason would be that their materials have good handling, such as an arbitrary working time and short setting time due to the light-curing system, and also have the advantage of comparatively low eost compared with porcelain restorations. However, it is well known that these materials cause a deterioration of the surface characteristics by water absorption or abrasion during elinical usage in the oral cavityT'8). Therefore, in order to take efficient measures against its deterioration, the paint-on resins, which were of a low viscosity due to applying them as a thin film on the surface and a light-activated polymerization type, have been produced9-ii). We have already reported that their toothbrush abrasion resistances were insignificantly different when compared with the eommercial resin for the crown and bridge usediO・i3・i4). Furthermore, effective painting layer or stability of optical properties and color were investigated from the standpoint of light transmittanceii'i2'i5). However, little is known of the effeet of water absorption on abrasion resistance of paint-on resins. The purpose in this study was to investigate the effect of water absorption on toothbrush abrasion and surface characteristics of ten resins for crown and bridge including the paint-on resins stored in distilled water at 37°C for 6 weeks, and to examine elinical application of the paint-on resins. MATERIALS AND METHODS