Effects of Calcium Fluoride Formation Induced by 1,450-ppm Fluoride Treatments on Surface Roughness of Demineralized Enamel

Abstract

  This study was aimed to clarify how calcium fluoride formation on the demineralized enamel surface influences surface roughness following treatment with an aqueous sodium fluoride solution containing 1,450-ppm fluoride.

  Mirror-polished bovine enamel specimens were initially demineralized for 24 hours, and then they were subjected to either twenty 3-minute immersions or one continuous 60-minute immersion in a fluoride solution. The control group was immersed in ultrapure water for 60 minutes.

  Alkaline-soluble fluoride (calcium fluoride) was extracted using potassium hydroxide and quantified using a fluoride ion-selective electrode. The surface roughness was evaluated using atomic force microscopy. Amounts of extracted calcium fluoride were significantly larger in both fluoride-treated groups than in the control, with the 60-minute immersion group yielding the highest values. Regarding surface roughness, the smoothing rate, defined as the percentage reduction in roughness achieved through fluoride treatment relative to the increase resulting from demineralization, was significantly higher in the fluoride-treated groups (25.3 and 40.0%, respectively) than control group (-2.6%). In the 60-minute immersion group, the surface roughness increased significantly after alkaline extraction. These findings suggest that treatment with a 1,450-ppm fluoride solution promotes calcium fluoride formation on demineralized enamel surfaces, thereby contributing to enhanced surface smoothness.