Chemical events during tooth dissolution.

Information on chemical changes during enamel dissolution has been collected from investigations on hydroxyapatite solubility, enamel solubility, artificial lesion formation, and natural caries. Although hydroxyapatite and enamel will ultimately dissolve in acid or during caries, compositional changes also occur. Most notably, there is a preferential dissolution of calcium, both from hydroxyapatite and from enamel, and of carbonate and magnesium from enamel. Root dentin yields substantial amounts of magnesium on acid attack. Fluoride may be involved in surface zone formation during attack, but an additional theory of coupled diffusion is described. Calcium-deficient mineral is produced during an acid attack, and this has lattice parameters and solubility behavior different from those of stoichiometric material. The interaction of fluoride produces a more stable lattice, resisting dissolution and favoring accretion, and tending to counteract the effects of carbonate and magnesium in forming mineral. The provision of fluoride, albeit at low levels, in plaque fluid is seen as being important in maintaining the net integrity of the tooth. More information is also needed on the role of the organic phase in tooth structures during caries and acid attack.