Abrasion biopsy in studies of mineral density of experimental enamel lesions

The profile of mineral density of experimental enamel lesions was determined by means of sampling with a new abrasion biopsy technique. Three types of lesions were produced on bovine enamel slabs: (1) pre-softened in lactic acid buffer for 16 hr; (2) pre-softened and exposed to a test for acid resistance for seven days; and (3) pre-softened, exposed to the seven-day Intra-oral Cariogenicity Test with extra-oral immersions in 1000 ppm F solutions for one min twice daily (ICT/F), plus the seven-day test for acid resistance. Lesions were assessed with measurements of surface microhardness, microradiography of thin sections, and abrasion biopsy. For abrasion biopsy of the experimental lesions, 15 parallel layers of approximately 10 microns each were abraded simultaneously with reference slabs of sound enamel on strips of lapping film. The depth of abrasion for each sample was calculated from the phosphorus content of the reference sample. Exposure to the ICT/F formed an acid-resistant zone within the lesion which diminished the microhardness change, although it did not have an appreciable effect on the total lesion depth as assessed with microradiography; abrasion biopsy indicated the formation of a mineral-dense zone within the lesion. This recently-developed technique of abrasion biopsy of experimental lesions offers the opportunity to link the composition of the lesion to controlled experimental conditions which will improve our understanding of demineralizing and remineralizing reactions on a standard tooth substrate.