The fluoride concentration in the enamel of permanent central incisors.

THE caries inhibitory effect of fluoride is well documented (Brudevold et a], 1967; Horowitz and Heifetz, 1970). •As the initial site of the caries lesion Occurs on the surface of the tooth at the plaque/tooth interface, the fluoride con­ centration in the surface layers of enamel is important in combating the carious process (Isaac et al, 1958; Naylor, 1969). The fluoride in the enamel is derived from the circulating plasma fluoride during the pre-eruptive phase. After eruption changes in the fluoride concen­ tration in the enamel arc related to the fluoride content of the drinking water and the saliva, and the ingested food (Fig1)X-ray diffraction and electron micro­ scopic studies led Gcrould (1945) to pos­ tulate that the fluorine in enamel is pre­ sent as fluorapatite. McCann (1953) showed that only fluorapatite can, in fact, form from the low concentration of fluoride in the tissue fluids and in drink­ ing water. The fluoride ion exchange which takes place both preand posteruptively is a simple hetero-ionic one between the fluoride ions in the solution phase and the dissimilar hydroxl ions in the solid phase (Joyston-Bechal, Duck­ worth and Braden, 1967). The reaction is as follows: Ca„, (P04), (OH). + 2F -> Ca„, (P04), F, + 2(OH) McCann (1969) referred to an addi­ tional mechanism for fluoride fixation in enamel. He observed that there was a higher fluoride retention when it was treated with an aluminium salt solution prior to the application of a topical fluoride solution. He suggested that fluorine can bind to polyvoient metal ions to form strong complexes. The object of this investigation was to determine the fluoride concentration in the surface layers of the enamel of central incisors of persons resident on the Witwatersrand. The drinking water in this area is supplied by the Rand Water Board and has an average fluoride concentration of 0.2 ppm.*