fluorapatite and zinc-phosphate

The present mechanistic in vitro study aimed to investigate dose-response effects of zinc and fluoride on caries lesion remineralization and subsequent protection from demineralization. Artificial caries lesions were created using a methylcellulose acid gel system. Lesions were remineralized for 2 weeks using citrate-containing artificial saliva which was supplemented with zinc (0-153 μmol/l) and fluoride (1.1 or 52.6 μmol/l) in a 7 × 2 factorial design. Lesions were also remineralized in the absence of zinc and citrate, but in the presence of fluoride. After remineralization, all lesions were demineralized for 1 day under identical conditions. Changes in mineral distribution characteristics of caries lesions after remineralization and secondary demineralization were studied using transverse microradiography. At 1.1 μmol/l fluoride, zinc exhibited detrimental effects on remineralization in a dose-response manner and mainly by preventing remineralization near the lesion surface. At 52.6 μmol/l fluoride, zinc retarded remineralization only at the highest concentration tested. Zinc enhanced overall remineralization at 3.8-15.3 μmol/l. At 76.5 and less so at 153 μmol/l, zinc showed extensive remineralization of deeper parts within the lesions at the expense of remineralization near the surface. Citrate did not interfere with remineralization at 1.1 μmol/l fluoride, but enhanced remineralization at 52.6 μmol/l fluoride. Lesions exhibiting preferential remineralization in deeper parts showed higher mineral loss after secondary demineralization, suggesting the formation of more soluble mineral phases during remineralization. In summary, zinc and fluoride showed synergistic effects in enhancing lesion remineralization, however only at elevated fluoride concentrations.

Topics: Animals; Apatites; Calcium Fluoride; Calcium Phosphates; Cariostatic Agents; Cattle; Citric Acid; Dental Caries; Dental Enamel; Dental Enamel Solubility; Dose-Response Relationship, Drug; Drug Synergism; Durapatite; Fluorides; Hydrogen-Ion Concentration; Lactic Acid; Methylcellulose; Microradiography; Minerals; Phosphates; Saliva, Artificial; Tooth Remineralization; Zinc; Zinc Compounds

Mouthrinses containing zinc ions inhibit plaque acidogenicity, but the effect is transient. Zinc-containing apatite or zinc phosphate precipitated within dental plaque might serve as a reservoir for zinc ions, thus providing prolonged inhibition of acid formation. Zinc-containing fluorhydroxyapatite was prepared from solutions containing CaCl2, KH2PO4, NaF and increasing amounts of ZnCl2 (0.0, 0.005, 0.02, 0.1, 0.2 or 1 mM; minerals No. 1-6, respectively) by raising the pH with ammonia. Zinc phosphate tetrahydrate (mineral No. 7) was prepared in a similar manner from a solution containing ZnCl2 and KH2PO4 only. Dense cell suspensions of Streptococcus mutans NCTC 10449 were incubated with 14C-glucose and one of the test minerals (No. 1-7). Glycolysis was allowed to proceed, with or without pH control, in a pH-stat. Samples were withdrawn at 1, 2, and 3 min, and extracellular glycolytic metabolites were identified by HPLC. Mineral No. 7 inhibited glycolysis and any pH fall almost completely. With the pH fixed at 5.5, reduction of glucose consumption and lactate formation was 83 and 93%, respectively, compared to the no-zinc control mineral (No. 1). No changes in glucose consumption or lactate formation were evident in the presence of minerals No. 2-6. All apatitic minerals had a buffering effect and, in the absence of pH control, glycolysis was increased due to the higher pH. Detectable levels of fluoride were not released by any mineral into the incubation mixture, and zinc only by minerals No. 6 and 7 in greater than trace amounts.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Acids; Ammonia; Apatites; Buffers; Calcium; Calcium Phosphates; Carbon Radioisotopes; Chlorides; Chromatography, High Pressure Liquid; Dental Plaque; Glucose; Glycolysis; Hydrogen-Ion Concentration; Lactates; Phosphates; Streptococcus mutans; Zinc; Zinc Compounds