Interaction of calcium hydroxide with zinc oxide-eugenol type sealers: a potential clinical problem

When a ZnOE type sealer was placed in root canals treated previously with calcium hydroxide dressing, an accelerated sealer setting rate occasionally occurred. This clinical observation led to the present experimental design aiming to investigate the effect of calcium hydroxide on a ZnOE cement and ZnOE type sealers and to preliminarily assess the removal efficiency of a calcium hydroxide preparation from root canal systems. Micro-MIR FTIR spectroscopy was used to quantify the effect of calcium hydroxide on the setting reactions of a ZnOE cement and two ZnOE type sealers. The removal efficiency of calcium hydroxide from root canal systems was evaluated after treatment with NaOCl; NaOCl and filing; and NaOCl plus EDTA and filing. Calcium hydroxide preferentially interacted with eugenol inhibiting the ZnO-eugenol chelate formation. The Ca(OH)2-eugenol interaction was rapid, and kinetically dependent, leading to residual eugenol in the set product. The set ZnOE cement and the ZnOE type sealers in contact with calcium hydroxide were brittle in consistency and granular in structure. Although none of the treatments tested completely removed calcium hydroxide from root canals, treatment with EDTA significantly reduced the extent of residual calcium hydroxide.