Laboratory study of the loads, speeds and times to finish and polish direct restorative materials

This study investigated the loads, speeds and times required to achieve the smoothest surface on samples of amalgam, composite resin and glass-ionomer cement using the four grades of a disc polishing system. The tests were conducted on a specially constructed jig. The restorations were abraded with the appropriate disc using a range of loads, speeds and times based on a previous practitioner study. The surface roughness of each material was measured before and after abrading. The load was varied first, followed by speed and finally time. Photomicrographs were taken of a sample finished at the optimum load, speed and time and of loads above and below the optimum that produced the smoothest surface finish. In addition the fractured edge of a sample finished at the optimum values was examined. There was an optimum load, speed and time that produced the smoothest surface for each restorative material. For amalgam and composite the surface roughness value decreased as the discs became finer. There was a reduction in the roughness value for glass-ionomer cement using the two roughest discs. The values obtained were substantially in contrast from the earlier practitioner study. There were specific values for load, speed and time that produced a smoother surface for each material.