Release of mercury vapor from dental amalgam

Because of its long-term clinical use there is more information and research data available about dental amalgam than about any other dental restorative material. However, on and off the safety of dental amalgam has been called in question and during the 80's the mercury controversy came to the fore, not only within the profession but also among the general public. Sources of mercury vapor contamination within dentistry were identified and attempts made to evaluate the contributions to the daily mercury uptake which can be attributed to dental amalgam. Mercury can be released from dental amalgam by evaporation and electrochemical corrosion as well as from amalgam particles which have been swallowed. A major route for mercury uptake from amalgam restorations is through inhalation of mercury vapor. The present study focused on experimental and analytical difficulties associated with the measurement of mercury vapor released in the oral cavity. A careful methodological study of the kind of source of mercury vapor that is prevalent and on the methods for measuring the intra-oral release of mercury vapor was carried out. With this as a basis quantitative determinations of the release rate of mercury vapor from amalgam restorations were made on healthy human subjects not occupationally exposed to mercury. The daily uptake of mercury from inhaled mercury vapor was calculated and salivary and urinary mercury levels were determined. In addition the release rate of mercury vapor from different types of amalgam was studied in vitro and in vivo. The findings may be summarized as follows: The only relevant measurable quantity when determining the mercury vapor released from amalgam restorations is the amount released per time unit, i.e. the amount of mercury vapor collected during intra-oral sampling is proportional to the sampling time. The diffusion of mercury atoms inside an amalgam restoration results in the formation of a concentration gradient in the surface of the amalgam. This mercury diffusion is the rate-determining step for mercury vapor release in the long run. In the short run the mercury concentration gradient prevalent on the amalgam surface on the measuring occasion is the apparent rate-determining step. The daily uptake of mercury from inhaled mercury vapor released from dental amalgam seems to make a very small contribution to the total body burden of mercury, in comparison with what can be tolerated in the work environment. The in vitro results revealed obvious differences regarding the release rate of mercury vapor from dissimilar amalgam types.(ABSTRACT TRUNCATED AT 400 WORDS)