Potential health hazards of ceramic ring lining material

Abstract

B ecause of the specter of cancer from asbestos, ceramic ring lining materials have been introduced as asbestos substitutes in industry and in dentistry. Although the toxicity of ceramic fibers to humans has not been studied, asbestos toxicity has been thoroughly examined and is important to consider if safer substitutes are sought. Asbestos is the generic term for a group of fibrous minerals that differ in physical form, chemistry, and toxicity. Of the many fibrous minerals, three major kinds of asbestos have been studied, white asbestos (chrysotile), blue asbestos (crocidolite), and brown asbestos (amosite). Extensive epidemiologic studies in humans with industrial or environmental exposure have shown that blue asbestos is the most toxic, brown asbestos is intermediate, and white asbestos, the type used in dentistry, is the least toxic.‘-‘5 Three diseases have been associated with asbestos exposure: asbestosis, a fibrotic thickening of the lung tissues causing impaired function; bronchogenic lung cancer; and mesothelioma, an always fatal tumor of the tissue lining the pleural cavity. Asbestosis and bronchogenie lung cancer (in the absence of smoking) have been shown to be dose-dependent, and thus preventable by reducing the amount of inhaled fibers longer than 5 Brn to below the threshold level (about 10 fibers/ml for white asbestos).), l5 Asbestosis and brochogenic lung cancer in the presence of smoking are not dosedependent; a synergistic reaction occurs, producing high incidence of both conditions.‘-4 Mesothelioma induction appears to be not only dose-dependent but also fiberdependent, and it is possible that only a few inhaled fibers of appropriate dimensions could induce fatal tumor formation. Even in circumstances in which blue asbestos was certainly the cause of fatal mesothelioma, fibers have been found in lung tissue in only 25% of the individuals.2 Intrapleural inoculation of rats has shown that not only does asbestos of all types induce mesotheliomas, but that these tumors may also be induced by man-made ceramic, glass, and aluminum oxide fibers.‘6*‘7 Intra-