Reactivity of young and old human enamel to demineralization.

The aim of this study was to determine the susceptibility of newly erupted and old permanent teeth to artificial, caries-like attacks. Two groups of caries-free teeth were used. Group 1 consisted of 38 teeth extracted for orthodontic reasons (9-12-yr-old children); group 2, of 40 teeth extracted for periodontal reasons (45-65-yr-old patients). After thorough cleaning, a test window was isolated on the incisal two-thirds of the buccal surface. After demineralization with 6% HEC gel at pH 4.9 for 8 days, longitudinal ground sections were prepared for imbibition studies in polarized light and for secondary ion mass spectrometry (SIMS). In the young teeth, the lesions appeared to be uniform in their extension in the enamel, whereas the old teeth showed less marked and thinner surface zones and greater depth of the positively birefringent body of the lesion. Polarized light microscopy and SIMS data support the hypothesis that there are different enamel pathways in the initiation of the natural carious process.