HAP Dissolution Study I: SnF2 vs. NaF Solution Study

Objectives: To compare the ability of 2 active ingredients normally used in dentifrice to inhibit HAP dissolution. Methods: HAP powder, a synthetic analog of enamel and dentine, was pretreated with test solutions (10g solution/300mg HAP powder) for 1 minute followed by 3x washing with water, then dried. 50mg of pre-treated HAP was exposed to 25 ml of acid dissolution media containing 0.10M lactic acid + 0.15M NaCl. pH of the media was adjusted to and maintained at pH 4.5. Exposure of HAP to the media results in dissolution and release of hydroxide ion, increasing pH of the solution. The increase in pH is compensated for by automatic additions of lactic acid (0.05M) to maintain the original pH (4.5) of the reaction cell (Metrohm Titrino). Total volume of titrant added after 30 minutes was used to calculate % reductions vs. non-treated HAP control. In this study, results were compared between NaF and SnF2 solutions to determine their relative ability to protect enamel against acid attack and dissolution. Results: Results showed that both SnF2 and NaF solutions have significant effect in slowing down the HAP powder dissolution compared with non-treated HAP under this experiment condition. The % reduction of dissolution (30 min) is significantly correlated with Log [concentration] of each ingredient. For SnF2 series: % Reduction Y = 15.867*Ln [F conc.]-13.703, R2=0.9884; For NaF series: % Reduction Y= 6.68*Ln [F conc.]+9.9915, R2=0.9596. At a given F concentration, eg. 280ppm, reduction in HAP dissolution for NaF was 47.6%, while reduction for the SnF2 treated sample was 75.7%. Conclusions: These results confirm that SnF2 was significantly stronger at attaching to HAP and inhibiting HAP dissolution than NaF solution. These results suggest the potential for SnF2 superiority in protecting enamel against acid attack and dissolution.