Histopathological evaluation of subcutaneous tissue reaction in mice to a calcium hydroxide paste developed for root canal fillings.

We aimed to evaluate the subcutaneous tissue reaction to a new calcium hydroxide paste for root canal fillings developed by Neo Dental Chemical Products Co., Tokyo, Japan. We injected calcium hydroxide paste and a water-based control subcutaneously into the dorsal area of 6-week-old anaesthetized male ddY mice. The tissue surrounding the injection sites was removed from mice in each group, 2 days, 1 week, 3 weeks and 12 weeks after the injection, and histopathologically examined. We found necrotic and degenerative changes, as well as foreign body reaction or proliferation of granulation tissue in specimens from both groups until 3 weeks after the injection. Some lymphocyte infiltration was observed in the 12-week specimens of the control group only. We conclude that calcium hydroxide paste is safe to use as a root canal filling material.