Transmission electron microscopy of cementum crystals correlated with Ca and F distribution in normal and carious human root surfaces.

Root-surface caries, like enamel caries, develops as a subsurface type of mineral loss. Very little is known about the composition of the surface zone covering the body of the lesion, and the ultrastructure and composition of carious cementum are not known. The aim of this study was to correlate the ultrastructure and arrangement of the cementum crystals with the distribution of fluoride and calcium in root cementum from human teeth with sound, unexposed, or exposed root surfaces as well as in early stages of root-surface caries. Microradiographically, unexposed specimens showed a relatively homogeneous mineral distribution contrasting with the formation of an apparently highly mineralized surface layer in exposed and, in particular, in carious cementum. The electron-probe findings showed a substantial fluoride peak corresponding to the surface layers in carious tissues in particular, whereas the calcium profile in the surface did not reflect the apparent increase in mineralization. A substantial increase in size of the cementum crystals was found in specimens with formation of the fluoride-rich, well-mineralized surface zone. The crystal lattice intervals when observed along the (001) plane showed a hydroxyapatite spacing. The findings indicated that a significant crystal growth can be achieved in human cementum concomitant with fluoride accumulation.