A study of porcelain surfaces as utilized in fixed prosthodontics

Thirty-six specimens of porcelain, including 18 vacuum-fired and 18 air-fired specimens, were brought to a high bisque bake under like conditions. Both types were divided into six groups to identify the dependent variables, while employing the usual procedures for "polishing" porcelain. These specimens were studied with a scanning electron microscope with the following results: (1) An unpolished, highly fired porcelain surface has a rather smooth appearance. (2) Treating the porcelain surface with sandpaper creates a rough surface with exposed bubbles. (3) The roughness of the porcelain surface after sanding is greatly improved with the use of polishing mediums. (4) A good smooth surface is not obtained unless the procedures are followed by a final glaze. (5) In each stage of polishing, the vacuum-fired porcelain has a smoother surface than the air-fired porcelain. Therefore, our conclusions are that vacuum-fired porcelain will tend to have a smoother surface, as viewed microscopically, than air-fired porcelain. The relative absence of bubbles in the former apparently allows the porcelain to be sanded and polished to a significantly superior finish. However, this study shows that, regardless of the usual polishing techniques, a final glaze presents the most acceptable surface.