EFFECTS OF SEVERAL FLUORIDE REAGENTS ON THE SURFACE STRUCTURE OF POWDERED DENTAL ENAMEL

¹ Department of Chemistry, Indiana University, Bloomington, Ind.

Electron diffraction and x-ray diffraction studies have been made of powdered dental enamel following treatments with several different fluoride reagents. Potassium fluoride causes a transformation of the apatite structure to one of calcium fluoride, the change is predominately upon the surface of the enamel, and the rate of transformation increases as the pH is lowered. Sodium monofluorophosphate does not result in a change of apatite structure to calcium fluoride structure during treatments for as long as one week in a 2 per cent solution at a pH as low as 2. Sodium silicofluoride also causes a transformation to calcium fluoride, but the rate is slower than that with an alkali fluoride, and the change develops somewhat within the particles rather than just on the surfaces. The effects of stannous fluoride are distinctively different from those of other reagents. The surface apatite structure is replaced by an amorphous structure, even during very brief treatments, and this amorphous substance may be rendered crystalline by heating. The mechanism must involve both the tin and the fluoride, because stannous chloride treatments result in practically no alteration of the original apatite structure.