No abstract

Microradiograms and their computer-aided image analysis of ground sections of the developing enamel of human permanent third molars and monkey permanent teeth (Macaca fuscata) indicate that the mode of progressive mineralization of enamel is completely different between the matrix formation and maturation stages. During the former stage, the enamel matrix is slightly mineralized. During the latter stage, which takes a much longer period than the previous stage, the increase in the secondary mineralization takes place first slightly, from the surface toward the inner layer, and then heavily, from the inner layer toward the surface. The narrow outer layer mineralizes very slowly during the middle and late stages of maturation, but finally achieves the highest mineralization of the entire enamel layer. The very narrow innermost layer mineralizes slowly without expanding its width. The former three processes seem to be under the direct control of the ameloblasts. Hypoplastic areas which appear during the matrix formation stages are not necessarily accompanied by hypomineralization. Dysfunction of the cells immediately after the completion of matrix formation appears to cause hypomineralization throughout the entire width of matrix except for the innermost layer. Disorders of the cells occurring during the middle and/or the late stage of maturation--due to chronic metabolic disturbances, such as fluorosis--induced hypomineralization localized mainly at the outer layer. The hypomineralized enamel is not necessarily accompanied by hypoplasia. The process of enamel mineralization is not necessarily fully synchronized with that of tooth eruption. Therefore, the narrow outer layer, especially in the fissure and cervical regions, is sometimes hypomineralized even after the teeth have erupted normally.

X-ray diffraction studies on calcified tissues (teeth and/or scales) of fish and of shark showed that the presence of fluoride affects the crystallite size and lattice parameters of the apatite phase. An inverse correlation between F contents (ranging from 0.2 to 3.8 wt% F) and alpha-axis dimensions (9.441 to 9.375 +/- 0.003 A) exists for both synthetic and enameloid apatites and is consistent with the F-for-OH substitution in the apatite, idealized as Ca10(PO4)6(OH)2 and Ca10(PO4)6F2, for fluoride-free and maximum fluoride-substituted apatite, respectively. In synthetic systems, the incorporation of F is found to be dependent on the F concentration of the media from which the apatite formed. This dependency is also observed between F content of the dentine apatites and the F concentration of the water from which the fish can (i.e., less than 0.08 ppmF in fresh water, about 1.3 ppm in seawater). However, no such dependency was observed between the F incorporation in fish enameloid apatite and the F concentration in the water of origin. In some cases, the F incorporated in the enameloid apatite is much in excess of what can be expected from the F concentration of water. These observations suggest that in some fish, a fluoride-concentrating mechanism is operative during the formation of the enameloid but not during the formation of the dentine, and this mechanism appears to be specie-related.

The progressive mineralization pattern of developing incisor enamel of rodents, (rats, bankvoles, mastomises and hamsters) was studied from the viewpoint of comparative histology.