An investigation of the potential biohazards associated with asbestos-substitute casting ring liners

Abstract

B ecause of the general concern about health hazards from asbestos, ceramic ring liners have largely replaced asbestos ring liners in dentistry. Steinbock and Asgar’ appear to have been the first investigators to report the use of ceramic liners. Priest and Homer’ subsequently presented photomicrographs showing the fiber morphology of ceramic and asbestos liners and commented that the fibrous ceramic liners should be safe for clinical use. Although results from several investigations have indicated that the ceramic ring liners can provide satisfactory casting accuracy for a variety of noble metal and base metal alloys,‘* 3-6 little research has been done to determine whether ceramic liners are a potential health hazard for dental personnel. There is a voluminous literature on the nature of asbestos and the medical problems that may result from its usage. Asbestos exposure has been related to bronchogenie carcinoma’ and to mesotheliomas of the pleural and peritoneal cavities.* Research has shown that the physical state of the respired particles, instead of the chemical composition, is the primary determinant of potential pathogenicity.’ The size, shape, and density of each individual fiber determine its aerodynamic behavior and the likelihood for deposition in the lungs. Long and thin fibers have the highest potential to induce tumors.‘O Such fibers cannot be engulfed by the macrophages of the immune system and burst the thin membranes of the cells, allowing enzymes to leak out and damage surrounding cells.” The fibers that present the greatest concern are those with diameters less than 3 pm and lengths greater than 20 pm. Fibers with diameters less