Cell death during tooth eruption in the rat: surrounding tissues of the crown

We investigated the occurrence of apoptosis and other types of cell death around the crown during tooth eruption of the rat upper molar. The TdT-mediated-dUTP-biotin nick end labeling (TUNEL) method and transmission electron microscopy (TEM) were employed. Apoptosis was detected by both TUNEL and TEM in part of the reduced enamel epithelium and connective tissue in the resorbing bony crypt of the pre-erupted tooth. In TEM, a large number of cells showed condensed chromatin and membrane-bound small bodies (apoptotic bodies). Macrophages that phagocytosed apoptotic bodies could be detected. Based upon the distance between bone surface and these apoptotic cells, and the characteristics of their organelles, we suggested that the apoptotic cells might be osteocytes, bone-lining cells (osteoblasts), and macrophages. We surmised that the osteoclasts had also died. Cells which contained autophagic vacuoles and autophagosomes, and others whose cytoplasm had dissolved, were also frequently observed. No progressive cell death was found in the oral epithelium or the fibrous connective tissue over the crown. These results suggest that apoptosis gives rise to some cell death during tooth eruption, but that other types of cell death also occur in various cells.