Critical Reviews in Oral Biology & Medicine, Vol 8, 136-153, Copyright © 1997 by International & American Associations for Dental Research
The effect of fluoride on apatite structure and growth
T. Aoba
Nippon Dental University, Department of Pathology, Tokyo, Japan.
Fluoride participates in many aspects of calcium phosphate formation in
vivo and has enormous effects on the process and on the nature and
properties of formed mineral. The most well-documented effect of fluoride
is that this ion substitutes for a column hydroxyl in the apatite
structure, giving rise to a reduction of crystal volume and a concomitant
increase in structural stability. In the process of enamel mineralization
during amelogenesis (a unique model for the cell-mediated formation of
well-crystallized carbonatoapatite), free fluoride ions in the fluid phase
are supposed to accelerate the hydrolysis of acidic precursor(s) and
increase the driving force for the growth of apatitic mineral. Once
fluoride is incorporated into the enamel mineral, the ion likely affects
the subsequent mineralization process by reducing the solubility of the
mineral and thereby modulating the ionic composition in the fluid
surrounding the mineral, and enhancing the matrix protein-mineral
interaction. But excess fluoride leads to anomalous enamel formation by
retarding tissue maturation. It is worth noting that enameloid/enamel
minerals found in vertebrate teeth have a wide range of CO3 and fluoride
substitutions. In the evolutionary process from elasmobranch through
enameloid to mammalian enamel, the biosystems appear 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 accelerating the kinetics of
remineralization) in the oral fluid bathing tooth mineral. Fluoride also
has been used for the treatment of osteoporosis, but much still remains to
be learned about maximizing the benefit and minimizing the risk of fluoride
when used as a public health measure.
