Dentinogenesis in the incisor teeth of adult rats after persisting  daily overdosage of 1α-hydroxyvitamin D_3, with special reference to osteodentin formation

Abstract

The dentinogenesis in the incisor teeth of adult rats that were orally administered with 0.1, 0.5 or 2.5μg/kg body weight (b.w.)/day of 1α-hydroxyvitamin D₃(1αOHD₃) for 30 days was studied with special reference to osteodentin formation. The decalcified maxillary incisors were examined by light and electron microscopy. Conspicuous osteodentin formation was observed only in the highest dose group. Small defects appeared at some intervals on the pulpal side of dentin in the middle-third of the tooth. The dentinal defects were occupied by many regressive odontoblasts, some of which were embedded in the irregular dentin just above the defects. Moreover, in the middle-third of the pulp, predentinoid tissue was frequently observed in the subodontoblastic area except for the regions where dentinal defects could be seen. Ultrastructurally, predentinoid tissue was composed of dense collagenous matrix containing small round membrane-bound vesicles similar to matrix vesicles. One or two cytoplasmic projections, which were very akin to bonafide odontoblast processes during early dentinogenesis morphologically, were often extended from the proximal aspect of the odontoblasts in contact with the predentinoid matrix.

A mass of osteodentin was observed in the apical-third of the dentin. From these results, we suggest that at least two different processes participate in the formation of osteodentin after the daily overdosage of 1αOHD₃, i. e., the partial regression of odontoblast population and predentinoid formation in the subodontoblastic area.