The progress of artificial caries-like lesions created in human, bovine, equine, and ovine enamel has been studied. Lesions were produced by exposure to an acid gel system or by 5-day exposure to a sequential batch culture technique using Streptococcus mutans NCTC 10832. Longitudinal ground sections were prepared. The lesions were of similar appearance in all species when examined in polarized light. The depth in human enamel was approximately half that in the animal species. Microradiography confirmed subsurface demineralization in all four species. Similar depth ratios were seen in the scanning electron microscope, but there were structural differences between lesions in human and animal teeth. Lesions in bovine teeth were more like those in human, but lesions in equine and ovine teeth were markedly different. Substitution of these animal enamels for human enamel in caries experiments demands that these differences be taken into account. Scanning electron microscopy is capable of resolving features in artificial caries lesions which cannot be differentiated by polarized light techniques. The latter will demonstrate generalized mineral loss, but scanning electron microscopy is required to characterize the sites of mineral loss.

It has been recognised for some years that it is possible to produce caries-like areas of demineralisation in human enamel using relatively simple acidified-gel techniques [Silverstone, 1966]. Attempts to produce similar lesions by means of bacterial action have, in general, been thought to require complex apparatus in the form of ‘artificial mouths’ [Pigman et al., 1952; Sidaway et al., 1964; Levine and Coulter, 1976; Yaari and Bibbby, 1976]. Such apparatus is expensive as well as being difficult to sterilise and maintain sterile. In most instances only one specimen can be processed at a time. Artificial ‘white spot’ lesions have been produced using sequential batch culture techniques [Jordan and Keγes, 1966] but doubt has been cast on the comparability of these lesions to natural caries [Hardie et al., 1971]. The present technique uses simple inexpensive apparatus which is easily sterilised and which can be readily replicated.