Response of dental follicular cells to the exposure of denuded enamel matrix in rat molars

Recent studies have indicated that cementum formation can be induced when d ental follicular cells are exposed to enamel matrix. The purpose of the pre sent investigation was to study this cementum formation and the appearance of the cells involved, including their expression of collagen types alpha 1 (I), alpha 1(II) and alpha 1(III) mRNAs, during this process by means of li ght microscopy and in situ hybridisation. The mandibular first molars of 5- d-old rats were surgically taken out, their enamel epithelium was removed, and then the crowns were re-inserted with the occlusal surface downwards in their crypts to allow the follicular cells to come in contact with the den uded enamel matrix. After observation periods of 2-14 d, the teeth were pre pared for light microscopic examination and in situ hybridisation. A monola yer of follicular cells in contact with the exposed enamel matrix changed t heir morphology and increased their expression of collagen type I mRNA as e arly as 2-4 d after exposure to the enamel matrix. A cementum-like tissue w as formed at the surface of the enamel matrix. Collagen type II mRNA was ne ver expressed in the tissues studied, whereas collagen type III mRNA was we akly expressed in the follicular cells throughout the experiment.