Effect of calcium hydroxide on bacterial lipopolysaccharide.

Apical periodontitis and its concomitant periapical osteolysis is caused by pulpal infection, and bacterial lipopolysaccharide (LPS) is known to play a major role in the bone resorption process. Little is known concerning the effect of root canal intervisit dressings on residual LPS in root canals after bacterial cell lysis. The purpose of this study was to evaluate the effects of calcium hydroxide on bacterial LPS. Free hydroxy fatty acids were quantified in samples of LPS treated with calcium hydroxide. Calcium hydroxide treatment of LPS was shown to release elevated quantities of hydroxy fatty acids. It was concluded that calcium hydroxide hydrolyzed the lipid moiety of bacterial LPS, resulting in the release of free hydroxy fatty acids. This result suggests that calcium hydroxide-mediated degradation of LPS may be an important reason for the beneficial effects obtained with calcium hydroxide use in clinical endodontics.