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Epidemiologic studies and caries experiments with animals have suggested that caries susceptibility of teeth decreases with age. Observations on the changes in the dental tissues and their environment with age have pointed out that a process commonly referred to as ‘posteruptive maturation’ of the dental enamel may be responsible. To test this assumption 10 unerupted third molars and 56 erupted human premolar teeth of various posteruptive ages were subjected for 130 days to an acid gel for caries-like lesion formation in vitro. Sections of the teeth were examined with polarized light and ‘contour maps’ were drawn with the approximate porosity of the lesions. The results were: unerupted = 833 μm (± 261); erupted of posteruptive age 0–3 years = 561 μm (± 150), 4–10 years = 470 μm (± 136), 11–30 years = 459 μm (± 192) and over 30 years = 297 μm (± 89). These findings show a decrease in the susceptibility of enamel to artificial caries with increasing age, which was especially marked at and shortly after eruption. This may be explained by a completion of mineralization of the outer enamel at about eruption, by a maturation process of the outer enamel posteruptively and by a reduction in the permeability of enamel occurring through to old age. The fluoride content of the mid-coronal buccal surface enamel under study was found to decrease posteruptively with age, therefore not accounting for the deceasing caries susceptibility.

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