Structure and mineral content of human exposed cementum and changes following phosphoric acid etching.

The structural and mineral content of human cervical cementum exposed in the oral cavi-ty and changes following a 30% phosphoric acid etching were investigated with scanning electron microscopy, electron-probe microanalysis, and atomic absorption spectrometry. Ca and P concentrations, and the Ca/P molar ratio of the exposed cementum were significantly higher than in the unexposed cervical cementum. However, there was no significant difference in the amounts of Ca dissolved from the exposed and the unexposed cementum by acid etching. These results indicate that the amounts of dissolved Ca may be affected by the amounts of organic fibrous material in the cementum. The acid etching strongly marked the ends of the extrinsic Sharpey's fibers in the exposed cementum, whereas in the unexposed cementum these structures were more or less difficult to differentiate from the intrinsic matrix following polishing and acid etching. The acid-influenced surface layers were divided into two zones; a completely demineralized surfaces zone showing organic fibrous structures and a partially demineralized subsurface zone, although the surface zone of the exposed cementum was covered with an organic felt-like sheath.