Air-Powder Abrasive System a new technique currently being promoted and it is aplication in dental clinic. The new polishing units are air-powered devices which use water and air pressure to deliver a stream of cleaning powder, which is mainly sodium bicarbonate.Effects and deposit removal areas are changed by varying working angles and distances, however, these differencesare not yet clear.In addition, effects on enamel, dentine and cementoenamel junction or removal of stain and deposits in pits and fissures are also unknown. Therfore, we examined these points, using an Air-flow in this study.The following results were obtained.1. The best working angle is 60° at a distance of 5 mm from tooth surface. Air-PowderAbrasive System cannot control extent of removal area.3. In the scanning-electron microscopic observations, the enamel surface is relatively undamaged but dentine and cementoenamel junction are markedly damaged. 4.There is no effect of stiking dental plaque on enamel by using the Air-Powder Abrasive System.

We investigated the bonding strength of hardened plastic teeth to denture base acrylic resin. Two types of hardened plastic teeth conventional plastic teeth and porcelain teeth were used. As the denture base acrylic resin, conventional heat-curing type and heatcuring type containing 4-META adhesive monomer were used. Test specimens were fabricated under four tooth ridge lap treatments, 1) no treatment, 2) grinding, 3) monomer application, and 4) grinding and monomer application.Then bonding strengths were measured according to JIS specification.The bonding strength of conventional plastic teeth to denture base acrylic resin did not differed with denture base acrylic resin and tooth ridge lap treatments. Also the variation coefficient of bonding strength of conventional plastic teeth did not vary with denture base acrylic resin and the treatments. The bonding strength of hardened plastic teeth to denture base acrylic resin were the same of larger than that of conventional plastic teeth to denture base acrylic resin. The bonding strengths of hardened plastic teeth to denture base acrylic resin were increased with tooth ridge lap treatments, but the variation coefficient of bonding strength of hardened plastic teeth were less varied with the treatments. These results were clearly observed in the use of denture base acrylic resin containing 4-META.

Maximum temperatures, time elapsed to reach them and setting times of four