44Ca doped remineralization study on dentin by isotope microscopy

Objective

The dental caries is developed as a result of an alternative course of mineral gain and loss. In order to distinguish between intrinsic Ca (tooth-derived mineral) and extrinsic Ca (solution-derived mineral) uptakes, a ⁴⁴Ca doped pH-cycling was performed using ⁴⁴Ca (a stable calcium isotope) remineralization solution.

Methods

The natural abundance of ⁴⁰Ca and ⁴⁴Ca is 96.9% and 2.1%, respectively. The remineralization solution was prepared using ⁴⁴Ca to contain 1.5 mmol/L CaCl₂ (⁴⁴Ca), 0.9 mmol/L KH₂PO_4, 130 mmol/L KCl, 20 mmol/L HEPES at pH 7.0. The pH-cycling was conducted on bovine root dentin daily by demineralization (pH 5.0) for 2 h, incubation in 0% (control) and 0.2% NaF (900 ppm fluoride) for 2 h and ⁴⁴Ca doped remineralization for 20 h. After 14 days pH-cycling, the specimens were sectioned longitudinally. On the sectioned surface, isotope imaging of ⁴⁰Ca and ⁴⁴Ca labeled mineral distribution was observed by a high mass-resolution stigmatic secondary ion 77 (Camera IMS 1270, Gennevilliers Cedex, France).

Results

Uptake of ⁴⁴Ca was greater in intensity for the 0.2% fluoride group than the control, especially in the superficial lesions. The control group showed ⁴⁰Ca (intrinsic) distribution in the subsurface lesions and in the superficial lesions, meanwhile the fluoride group showed ⁴⁰Ca distribution limited in subsurface lesions. The total Ca (⁴⁴Ca + ⁴⁰Ca) image revealed more homogeneously for the control than the fluoride group.

Significance

Since the fluoride-treated surface is more acid-resistant than intrinsic dentin, alternative minerals were dissolved from the intact intrinsic lesion in the demineralization cycle.