[Barrel finishing of cobalt-chromium alloy cast plate--basic study on polishing materials and time]

This study was designed to establish the optimum grinding condition of barrel finishing for cobalt-chromium alloy. Smoothing of the mucosal surface, reduction of labor, and improvement of the working environment were estimated by the application of barrel finishing to cobalt-chromium alloy.

Tabular test pieces cast in cobalt-chromium alloy whose surface was standardized by waterproof abrasive papers were used in this study with a centrifugal flow barrel finishing machine. The abrasive that was most suitable for the primary polishing was selected, and proper polishing time was then decided by measuring the surface roughness of the test pieces. The abrasive and polishing time for the secondary polishing were decided in the same manner. Finally, the surface texture of the test pieces, which were finished in this condition by the manufacturer's instruction or by the electrolytic polishing method, were compared. Statistic analysis was performed by one-way analysis of variance and the multiple comparison test.

A triangular prism-shape abrasive made of Al(2)O(3) and SiO(2) whose one side or height was 6 mm was selected for the primary polishing, and the same kind of abrasive with one side or height of 4 mm was chosen for the secondary one. The optimum polishing time for the primary polishing and the secondary polishing were 60 minutes and 40 minutes, respectively. The surface roughness of the test pieces that were finished in this condition was significantly smaller than that finished following the manufacturer's indication or that finished by the electrolytic polishing method.

The optimum polishing condition of barrel finishing for cobalt-chromium alloy was established in this study. For the polished surface of cast dentures, polishing by a rotary cutting instrument after barrel finishing in this condition would be needed, as no luster was observed on the finished surface.