Physiological resorption of connective tissue associated with tooth eruption

The ultrastructural changes occurring during physiological resorption of connective tissue associated with erupting teeth of monkeys is described. Significant differences occur before and after the tooth emerges into the oral cavity. Before the tooth erupts connective tissue resorption over the tooth shows a cellular response involving cells of the fibrocytic and monocytic series. The cells of the fibrocytic series show changes from the resting fibrocyte which involve dilation of the cisternae of the rough endoplasmic reticulum, hypertrophy of the Golgi appearatus, the apparance of agranular vesicles, loss of the spiral configuration of polysomes and the development of numerous coated vesicles close to the cell surface. Ultimate breakup of the fibrocyte occurs. Monocytic cells become macrophagic. No breakup of macrophages occurs. In the extracellular compartment the collagen fibrils show a breakup into smaller units and eventual loss. The dental epithelium associated with this disorganized connective tissue is characterized by the development of numerous coated vesicles and a highly vesicular cytoplasm. The connective tissue and dental epithelium lateral to the crown of the tooth showed a similar ultrastructural picture which alters significantly as the tooth emerges into the oral cavity and the epithelial attachment develops. An acute inflammatory response occurs and the connective tissue supporting the forming attachment shows areas of breakdown and synthesis occurring simultaneously. These findings are discussed in terms of the mechanism of connective tissue breakdown and the fibrocyte implicated as playing an important role in this mechanism. It is suggested therefore, that the fibrocyte is capable of modulation to become either synthetic, maintaining or degradative.