Dental caries.

Since the beginning of this century it has been widely recognized that micro-organisms constitute an essential factor in the pathogenesis of dental caries. Indirect proof of this concept came when McClure and Hewitt (1946) observed that the inclusion of penicillin in a normally cariogenic diet resulted in a substantial reduction of caries in rats. Using gnotobiotic techniques, Orland et al. (1954) showed that rats fed a diet which is normally cariogenic failed to develop dental decay in the absence of bacteria. This observation was con- firmed and extended by Fitzgerald and Keyes (1960).