The development of a cementum layer over the enamel surface of rabbit molars—A light and electron microscopic study

Abstract

The deciduous molars of the rabbit, which are of finite growth, erupt between 4 and 5 days after birth. After 4 weeks, the six deciduous maxillary molars and the four deciduous mandibular molars are replaced by an equal number of continuously erupting premolars. In addition three permanent molars of continuous growth eventually form in each quadrant, posterior to the premolars. Both deciduous and permanent teeth develop a substantial amount of cementum over their enamel surface. Its formation follows the loss of continuity of the reduced enamel epithelium. The cementum which forms within the developmental groove of these teeth contains many cellular inclusions and is of a fibrillar nature, that is it contains recognizable collagen fibrils in its organic matrix. The cementum on the periphery of the crowns, particularly of permanent teeth, is primarily acellular and consists of both fibrillar and afibrillar cementum, the latter containing no recognizable collagen fibrils in its organic matrix. Degeneration of some cellular elements of cellular cementum as a result of continuous eruption is accompanied by the appearance of dense bodies resembling lysosomes and autophagic vacuoles within these cells. These changes are not observed in connection with the disappearance of reduced enamel epithelial cells prior to the onset of cementogenesis.