[Fibrous components and lamellar structures in cementum].

The purpose of this study was to clarify the relationship between the lamellar structure and the fibrous components of cementum. Freeze-fracture specimens and ground sections of the human molar cementum were treated with acid- and/or alkaline-solutions, then examined by scanning electron microscopy. Both of the layers of Sharpey (extrinsic) fiber and matrix (intrinsic) fiber were distinguished in freeze-fracture specimens and ground sections, but no lamellar structures appeared. For the first time, the lamellae isolated with narrow grooves were clearly observed on the ground sections that were treated with 5% sodium hypochlorite for 60 min followed by 0.5-1.0 M hydrochloric acid for 30-60 sec. In addition to the two fiber-layer types, the mixed fiber layer containing both components of matrix and Sharpey's fibers was classified, and the lamellar arrangement of matrix fibers was also revealed. When the hypochlorite treatment time was prolonged for 120 min, the lamellar structures were evident. Our results show that those treatments may resolve the regions of physiological hypomineralization related to the incremental lines running parallel to the cemento dentinal junction and the lines of discontinuity of the fibrous components.