Influence of sodium chloride on fluoride reactions with dental tissues.

Abstract

Owing to previous findings of an enhanced fluoride (F) uptake by enamel surfaces in the presence of elevated NaCl concentrations, accompanying solubility changes were studied on homologous pairs of extracted premolar teeth and on powdered enamel and dentine. The enamel surfaces and the enamel and dentine powders were exposed to solutions of NaCl and NaF, the NaCl concentrations corresponding to either F-salted food or saliva, the NaF concentrations to either F-salted food or fluoridated water. Subsequently, the surfaces and powders were exposed to 0.2 <i>M</i> acetate buffer, pH 4. The slight dissolving effect of the NaCl-NaF solutions was investigated by calcium analysis and the loss of F from solution to tooth substance was determined. The subsequent dissolution in acetate buffer was studied by calcium and F analyses and by determination of the weight losses and the levels of F remaining in the enamel and dentine powders. The results showed (1) that intact enamel surfaces were moderately affected by 175 m<i>M</i> NaCl when F was present in a proportion corresponding to fluoridated salt; (2) that this chloride concentration had a dissolving effect on the fine-crystalline dentine apatite; (3) that the enamel and dentine solubility in acid was reduced nearly as much by the lower as by the higher F concentrations studied; (4) that F dissolved by acid seemed to counteract simultaneous calcium dissolution, and (5) that dissolved F was recombined to a great extent by apatite present in a fine-crystalline form.