Intra-oral models: comparison of in situ substrates.

Numerous intra-oral caries models have been designed for clinical and mechanistic purposes. Several factors--such as human vs. bovine enamel, sound vs. demineralized tissues, lesion type, dentin vs. enamel, the severity of the cariogenic challenge, and the microflora--may influence the reactivity of the hard tissue and hence lesion development and progression. Some models use unextracted teeth and are true in vivo models, whereas in situ models are based on hard-tissue substrates in the form of slabs or sections. Models producing a moderate cariogenic challenge usually show a fluoride dose response. However, caries is increasingly becoming a problem limited to some high-risk patients and to lesions located to areas where severe challenges exist (e.g., fissures and pits). There is thus need for models that could mimic such situations. One of the requirements for intra-oral models producing severe cariogenic challenge conditions should probably be that it should be able to demineralize fluorapatite. A challenge for future caries research is to develop agents that have a better clinical effect in fissures and pits than those presently available. Because, in the past, much emphasis has been placed on remineralization of artificial lesions, more research on the demineralization process should be performed in the future, since this may give improved clinical effects. Ideally, an intra-oral caries model should take into account as many of the natural oral conditions as possible and minimize the degree of artificiality.