New method for divesting cobalt-chromium alloy castings: Sandblasting with a mixed abrasive powder☆☆☆★★★♢

Statement of problem. Because the conventional divesting method for cobalt-chromium (Co-Cr) alloys is laborious, a more convenient method is desirable. Purpose. This study compared sandblasting with a mixed powder composed of aluminum oxide and glass beads to sandblasting with single powders (carborundum, aluminum oxide, and glass beads) when a Co-Cr casting was removed from the investment mold. Material and methods. Rectangular plates with the 2 surfaces simulating the inner and outer surfaces of a removable partial denture framework were fabricated with Co-Cr alloys. Four kinds of sandblasting powders were used to remove the remnants of investment molds. Total time (seconds) required for each procedure was measured, as was the surface roughness (Ra) of each specimen after sandblasting. SEM was used to analyze the powders themselves and the sandblasted specimen surfaces. Results. Glass beads alone and the mixed powder of aluminum oxide and glass beads generated a smoother surface compared with aluminum oxide and carborundum powders. The use of the mixed powder significantly reduced the time of the sandblasting procedure. SEM revealed that glass beads generated fewer scars, followed by the mixed powder and then aluminum oxide. The surface sandblasted by carborundum powder was always the roughest. Conclusion. Sandblasting Co-Cr castings with the mixed powder effectively decreased treatment time and resulted in smooth, clinically acceptable casting surfaces. (J Prosthet Dent 2001;85:357-62.)