Hard-tissue resorption and deposition after endodontic instrumentation.

Hard-tissue resorption and deposition following endodontic instrumentation were studied histologically in forty-one monkey teeth after 2, 7, and 42 days. No medicaments and no root canal filling materials were used. The number and length of lacunae and areas of resorption of the root canal wall, the root surface, and the lamina dura were counted and measured. Resorption, stimulated by instrumentation, was observed after 7 days at all sites. Resorption was slight at the root canal wall and at the root surface and was significantly more severe than normal osteoclastic replacement in the adjacent lamina dura. After 42 days the reaction had subsided at the three sites, but none of the tissue had returned to normal. Inflammatory reaction due to infection of the root canal appeared to enhance resorption after 42 days at the root canal wall and the lamina dura, but this was not observed at the root surface.