EARLY CELLULAR EVENTS IN AN ACTINOMYCIN-D-CREATED DENTIN NICHE IN THERAT INCISOR

Administration of actinomycin D at a dose level of 0.375 mug/g resulte d in the selective disruption of developing odontoblasts at a critical stage of morphogenesis. A dentin niche was formed which was later rep aired by cellular reparative dentin. The cellular changes which result ed in dentin niche formation were studied histologically and ultrastru cturally in serial longitudinal and transverse sections from tissues o btained 10 h to 80 h following injection of the drug. Five stages were identified: initial destruction (10-20 h), rapid destruction (30-40 h ), debris removal (50-60 h), proliferation (60-80 h) and matrix deposi tion (post 80 h). The cellular changes found in the dental papilla wer e considerably different from those found in inflammation, resolution and repair of fibrous connective tissue. These early stages were domin ated by apoptosis and heterophagy, and after 80 h by disordered dentin matrix formation. The three-dimensional morphology of the defect was reconstructed from serial sections. The shape of the niche was the res ult of interference by actinomycin D in the patterns of proliferation and migration of the cells in the apical region of the rat incisor too th.