Effect of Setting-condition and Medium pH on Long-term Fluoride Release

Objectives: Test the hypothesis that setting-condition and pH of storage medium have no influence on the fluoride releasing of fluoridated glass filler containing materials.
Methods: Disks (10mm diameter and 1mm thick) were prepared from Chemfil™Rock (CR), Ketac™Molar (KM), Fuji IX™ (F9), Ketac™Nano (KN)and Dyract^®eXtra (DX). After preparation, disks were allowed to set in humidor or in vacuum at room temperature for 48h. Three acetate-based pH buffers (4, 6 and 8) were used for fluoride release. Disks (N=7 for each test group; total N=210) were stored individually in vials with 5mL of buffered solution and stored in 37°C incubator. At prescribed time intervals up to 400d, the solutions were replaced, and the solution fluoride content and pH were determined. Cumulative release data (Y, µg/mm²) were fit to Y=a+b●(time)^½ by linear regression to estimate a and b (coefficient of Fickian release).
Results: Two-way ANOVA's of the regression results show that the influences of pH and setting-condition on the value of b are significant (p<0.001). One way ANOVA’s for each material-setting group show that releases in pH6 are in the lower group (lower b values) and releases in pH4 are in the higher group (higher b values) for all material-setting groups. In pH8, CR and F9 are in the higher release group that associated with surface degradation, the reaming materials without signs of degradation were in the lower release group. Student’s t-tests show in-vacuum disks with evident crazes on surface exhibited significantly higher (p<0.0001) release for most material-pH groups, except forCR-pH4 (p=0.9225) and DX-pH6 (p=0.2133).By the sign of a values, all DX groups and most groups in pH8 exhibited delayed releases. Changes of pH were minimal.
Conclusions: The hypothesis is rejected. In addition, the influence of setting-condition and pH are also material dependent.