X-Ray Diffraction Study of the Reaction of Acidulated Fluoride with Powdered Enamel

¹ Laboratory of Histology and Pathology, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland

X-ray diffraction studies have been made of powdered enamel before and after treatment with an acidulated phosphate-fluoride solution. The acid solution reacted rapidly with finely divided enamel to form large amounts of calcium fluoride. The solution reacted with larger particles of enamel (44-250µ) to form some calcium fluoride, but the rate was much slower and the change to calcium fluoride appeared to have been self-limiting after about 2 hours. An increase in crystallinity was observed after 62 hours' treatment. A decrease in the a-axis parameter indicated that fluoride ion substitution for OH groups had taken place, thus forming some fluorapatite.