Effect of Salivary Proteins on Enamel Remineralization In Vitro

Previously, we reported that the rate and extent of enamel remineralization in vitro was enhanced by buffered acidic solutions, by reducing preferential remineralization of the outer enamel surface and promoting the flux of mineral ions into inner lesion portions. Objective: This study was carried out to test the hypothesis that specific salivary proteins can enhance the rate and extent of enamel remineralization by adsorbing to crystals within the porous enamel surface of artificial lesions to similarly prevent preferential surface remineralization. Methods: Thin sections (n=5-7) of human enamel with pre-formed artificial subsurface lesions were treated with either 50mM NaCl solution (control), 16µM histatin1 in 50mM NaCl, or 15µM statherin in 50mM NaCl for 24 hours. The sections were removed and blotted with tissue paper, before each being immersed in 20mL of remineralizing solution (1.5mM CaCl₂, 0.9mM KH₂PO₄, 10ppm F, 50mM lactic acid, pH 7) at 25^oC. Quantitative microradiography was used to assess changes in mineral content at selected times (up to 650 h). Results: Histatin-1 was found to significantly enhance the overall rate and extent of remineralization, while statherin had little to no effect. By the end of the experiment, a 54% greater mineral recovery (normalized to lesion size) on average was achieved for lesions exposed to histatin-1, in comparison to controls (not exposed to protein) and those exposed to statherin which did not differ significantly in this respect. However, results indicated that, in contrast to control sections, exposure to both histatin-1 and statherin enhanced mineralization in deeper portions of the lesions relative to that which took place in the enamel surface. Conclusion: Results obtained are consistent with the proposed hypothesis and suggest that observed differences may be related to differences in protein properties and their relative affinities for mineral surfaces. Supported by NIH/NIDCR grants DE-15163, DE05672, DE07652 and DE14950.