Remineralization of bovine incisor root lesions in vitro: the role of the collagenous matrix.

This study deals with the role of collagen in the remineralization of bovine incisor root lesions. The degradability of the collagenous matrix after in vitro remineralization was also investigated. The root surfaces were exposed to 0.1 M acetic acid, pH 4.0, to produce erosive lesions or to 0.1 M lactic acid, 0.2 mM methane hydroxy diphosphonate, pH 5.0, to produce subsurface lesions. After demineralization, the roots were subjected to remineralization, with or without prior treatment with a bacterial collagenase to remove accessible collagen. Remineralization was carried out in solutions with a Ca/Pi molar ratio of 1.67, and [Ca]. [Pi] concentration products of 0.6, 1.35 or 2.4 mM2, with all solutions having an ionic strength of 0.15 M, and a pH of 7.0. After remineralization, the roots that were not treated with collagenase were incubated with the enzyme. The results indicate that remineralization of erosive lesions is surface-controlled and that of subsurface lesions diffusion-controlled. For both lesion types it was shown that the removal of collagen before remineralization did not affect the rate of mineral deposition in the root lesions. Nevertheless, remineralization in those lesions where accessible collagen had not been removed resulted in a significant reduction in the amount of degradable collagen. The observations of this study suggest that remineralization did not occur by nucleation of mineral on the organic matrix but rather by growth of residual crystals in the partially demineralized root tissue.