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Earlier studies have indicated an increased mineral content in the surface layer of cementum which has become exposed to the oral cavity as a result of gingival retraction. The purpose of this study was to characterize this process more precisely by elemental analysis. Serial ground sections of suitably embedded teeth from residents of a nonfluoridated area were microradiographed. Sections showing exposed cementum with an increased radiopacity of the surface layer were processed for electron probe analysis and electron microscopy. Characteristically, the radiopaque zone had an elevated Ca and P content (7–10 % increase), unchanged Mg, extremely high F (up to 1.9 %) and elevated S (0–100 % increase), as compared to unexposed cementum. The highest F values occurred concomitantly with the highest Ca and P. F showed a rapid drop and a leveling‐off at a varying distance from the root surface. Electron microscopy showed increased crystal size and improved crystallinity in the hypercalcified layer, while demineralized sections indicated an alteration of the organic matrix. In the absence of detectable caries, exposed cementum may develop a highly calcified surface layer, an F content higher than any other calcified tissue, as well as a subsurface condensation of organic material of exogenous origin.
Selvig et al. (Thu,) studied this question.