Formation of intermediate cementum. II: a scanning electron microscopic study of the epithelial root sheath of Hertwig in monkey.

The intermediate cementum is a layer of calcified tissue between the dentin and the cementum at the periphery of dental roots. The mineralization pattern of the intermediate cementum and the innermost layer of aprismatic enamel in the crowns has been shown to be very similar. Since the formation of these tissues is incompletely known and there have been diverging opinions whether they are of epithelial or mesenchymal origin, the present study aimed at investigating the surface morphology of the root sheath with scanning electron microscopy and correlate it to the mineralization of the intermediate cementum. The advancing mineralization front of the intermediate cementum was covered by the root sheath. Numerous microvilli facing the root were found on this part of the root sheath. The corresponding surface facing the dental follicle was covered with bulb-type junctions. Microvilli and bulb-type junctions have also been demonstrated on the surface of the presecretory ameloblast and associated with formation of aprismatic enamel. Thus, the epithelial root sheath seems to actively take part in the formation of intermediate cementum.