Experimental internal resorption in monkey teeth

Internal resorption is a rare pathological finding except in pulpectomized deciduous teeth. Although its etiology is largely unknown, infection and trauma have been suggested in a number of cases. The aim of this study was to explore the possibility of provoking internal resorption in vivo , to study etiological factors such as trauma and infection, and to describe the cells colonizing the walls of the pulp chamber. Monkey incisors were opened, injected with Freund's complete adjuvant and sealed or left open to the oral cavity. After varying observation periods, the teeth were extracted and prepared for examination with scanning electron microscopy, microradiography, light microscopy and enzyme histochemistry. Colonization of the walls of the pulp chamber by macrophage‐like cells was observed in both experimental groups. However, it appeared to be transient in Unsealed, non‐infected teeth and more extensive and prolonged in the open, infected teeth. In sections of pulp tissue a tartrate‐resistant acid phosphatase activity characteristic of mineralized tissue resorbing cells was evident. It is suggested that internal resorption may be divided into a transient type and a progressive type, the latter requiring a continuous stimulation by infection.