Effect of Salivary Fluoride Levels on Demineralisation of Enamel

Objectives: The purpose of this study was to examine the effect of fluoride levels similar to those reported for saliva from high and low fluoride areas (0.02ppm, 0.05ppm) on the demineralisation of human permanent and deciduous enamel. Methods: An adaptation of the method by Robinson et al., 1992 was used. Sections of sound enamel were placed in a vial containing demineralising solution [2.0mM Ca(NO3)2, 1.2mM KHPO4 in 50mM acetic acid, pH4.8] for 1 hour. The demineralising solution contained 0, 0.02 or 0.05ppm fluoride, added as NaF. 20ul aliquots were taken from the supernatant solution at 1,2,3,4,5,6,7,8,10,12,14,16,18,20,30,40,50 and 60 minutes. The mineral loss was evaluated quantitatively on a volume percent basis by the amount of phosphorus which was dissolved from the enamel into the solution and the volume of enamel exposed. It was assumed that all mineral present was in the form of hydroxyapatite. The phosphorus content was determined by a modification of Chen et al.,1956. Results: When the demineralisation curves for fluoridated and non-fluoridated demineralising solutions were compared, there were obvious differences. Overall, there was a significant decrease in the net mineral loss when the non-fluoridated solution was compared with the fluoride experiments for permanent enamel (p<0.001) but deciduous enamel showed no significant difference between no fluoride and 0.02ppm. For both there was a difference (p<0.001) between 0.02 and 0.05ppm experiments. When the demineralisation curves for deciduous and permanent enamel were compared, there were also differences. The most intriguing difference was that deciduous enamel demineralised through a repeated pattern of demineralisation and remineralisation. This pattern was not clearly seen in permanent enamel. Conclusion: A salivary fluoride level of 0.05ppm had a protective effect against demineralisation and seemed more effective for permanent enamel than deciduous enamel which might be due to differences in composition and structure.