Investigation of Fluoride Release from Orthodontic Acrylic Plate

Abstract

Objective: This study aimed to investigate fluoride release, flexural strength and surface characteristics of three orthodontic acrylic resins (A) blended with (1) sodium fluoride powder (NaF), (2) calcium fluoride powder (CaF2), and (3) glass ionomer cement powder (GIC). Material & Methods: Acrylic resin was blended with NaF, CaF2 , and GIC to make orthodontic acrylic plates. Each sample group was divided into subgroups at fluoride concentrations 5%, 10% and 20%. The acrylic resin was cured in a round stainless steel mold and kept in a bottle with 10 ml. deionized water then kept in an incubator at 37oC. The deionized water, changed every day, was tested for fluoride release up to six mo by Orion machine. For the flexural strength test, the samples were cured in a stainless steel mold, 64 mm. long, 10 mm. wide and 3.3 mm. high according to standard of ISO 20795-2 and testing was done up to 6 mo in deionized water. Scanning electron microscope determined surface characteristics after being blended. Results: Fluoride release was observed from orthodontic acrylic plates blended with NaF, CaF2 and GIC. The results of the A-NaF and the A- CaF2 group decreased fluoride level greatly at day 2, but the A-GIC group was observed at day 7. The A-NaF group and the A-GIC group could not detect fluoride level after mo 4 and 2, respectively. The A-CaF2 group found greater long term fluoride release than the A-NaF and the A-GIC group especially at 20% concentration (up to six mo). Significant differences (p<0.05) of fluoride release level (ppmF) among the A-NaF, A-GIC, and A-CaF2 groups at 5% concentration in every time point from day 1 to the mo 5, but not significant in mo 6 similar to the 10% concentration comparison. Whereas, comparing the 20% concentration among groups, significant differences (p<0.05) were found between groups in all periods of time (from the day 1 to mo 6). When comparing the different concentrations of 5%, 10%, and 20% in each group, significant differences (p<0.05) were found in every concentration at every time period of the A-GIC group from day 1 to mo 2, in the A-CaF2 group from day 1 to mo 6 and in the A-NaF group from day 1 to mo 4. Conclusion: Fluoride release was observed from orthodontic acrylic plates blended with NaF, CaF2 and GIC. The longest duration of fluoride release from orthodontic acrylic plates was found in the CaF2 group followed by the NaF and GIC groups. The flexural strength in every group decreased over time. This result implied that the flexural strength decreased during fluoride release. The acrylic surface was seen to be porous in every period of the fluoride release process.