CHARACTERIZATION OF CELLULAR-RESPONSES INVOLVED IN REPARATIVE DENTINOGENESIS IN RAT MOLARS

During primary dentin in formation, differentiating primary odontoblas ts secrete an organic matrix, consisting principally of type I collage n and non-collagenous proteins, that is capable of mineralizing at its distal front. In contrast to ameloblasts that form enamel and undergo programed cell death, primary odontoblasts remain metabolically activ e in a functional tooth. When dentin is exposed to caries or by operat ive procedures, and when exposed dentinal tubules are treated with the rapeutic dental materials, the original population of odontoblasts is often injured and destroyed. The characteristics of the replacement po ol of cells that form reparative dentin and the biologic mechanisms th at modulate the formation of this matrix are poorly understood. Based on the hypothesis that events governing primary dentinogenesis are rei terated during dentin repair, the present study was designed to test w hether cells that form reparative dentin are odontoblast-like. Cervica l cavities were prepared in rat first molars to generate reparative de ntin, and animals were killed at various time intervals. In situ hybri dization with gene-specific riboprobes for collagen types I and III wa s used to study de novo synthesis by cells at the injured dentin-pulp interface. Polyclonal antibodies raised against dentin sialoprotein (D SP), a dentin-specific protein that marks the odontoblast phenotype, w ere used in immunohistochemical experiments. Data from our temporal an d spatial analyses indicated that cells forming reparative dentin synt hesize type I but not type III collagen and are immunopositive for DSP . Our results suggest that cells that form reparative dentin are odont oblast-like.