THE EFFECT OF FLUORIDE ON APATITE STRUCTURE AND GROWTH

Fluoride participates in many aspects of calcium phosphate formation i n vivo and has enormous effects on the process and on the nature and p roperties of formed mineral. The most well-documented effect of fluori de is that this ion substitutes for a column hydroxyl in the apatite s tructure, giving rise to a reduction of crystal volume and a concomita nt increase in structural stability. In the process of enamel minerali zation during amelogenesis (a unique model for the cell-mediated forma tion of well-crystallized carbonatoapatite), free fluoride ions in the fluid phase are supposed to accelerate the hydrolysis of acidic precu rsor(s) and increase the driving force for the growth of apatitic mine ral, Once fluoride is incorporated into the enamel mineral, the ion li kely affects the subsequent mineralization process by reducing the sol ubility of the mineral and thereby modulating the ionic composition in the fluid surrounding the mineral, and enhancing the matrix protein-m ineral interaction, But excess fluoride leads to anomalous enamel form ation by retarding tissue maturation. It is worth noting that enameloi d/enamel minerals found in vertebrate teeth have a wide range of CO3 a nd fluoride substitutions. In the evolutionary process from elasmobran ch through teleost enameloid to mammalian enamel, the biosystems appea r to develop regulatory functions for limiting the fluoridation of the formed mineral, but this development is accompanied by an increase of carbonate substitution or defects in the mineral. In research on the cariostatic effect of fluoride, considerable emphasis is placed on the roles of free fluoride ions (i.e., preventing the dissolution and acc elerating the kinetics of remineralization) in the oral fluid bathing tooth mineral. Fluoride also has been used for the treatment of osteop orosis, but much still remains to be learned about maximizing the bene fit and minimizing the risk of fluoride when used as a public health m easure.