An in vitro investigation into the wear effects of glazed, unglazed and refinished dental porcelain on an opposing material.

A machine designed to simulate the physical parameters of masticatory function was used to investigate the amount of wear produced on perspex plates opposing discs of porcelain which were glazed, unglazed or finished to varying stages of a polishing sequence recommended with a proprietary finishing kit. The perspex specimens were abraded, under water at 37 degrees C for a total of 800000 contacts using a contact time of 0.2 s, a sliding distance of 15 mm and a constant load of 0.19 N/mm2. Assessments of the wear of the perspex were based upon depth measurements of the wear track recorded on surfometric tracings. Further measurements of the cross-sectional area of the wear track were made using an image analysing computer. The investigation confirmed that the best finish and least abrasive surface was produced by glazing of porcelain. The finish produced by intermediate components of the proprietary finishing kit did not reduce the abrasiveness of the porcelain surface. It was necessary to complete the polishing sequence with diamond paste to achieve a surface which approached the wear characteristics of glazed porcelain. It is recommended that any adjusted porcelain restoration should be re-glazed or subjected to a finishing sequence which is followed through to a final stage of polishing with a diamond paste.