pH Changes at the Surface of Root Dentin after Intracanal Dressing with Calcium Oxide and Calcium Hydroxide

This study was designed to compare pH changes at the cervical and apical surfaces of root dentin after canal obturation with calcium oxide or calcium hydroxide pastes. The effect of the exposure to CO2 on the pH at the root surface also was assessed for both materials. Thirty-six extracted human canines were selected and instrumented. Wells 1 mm deep x 1.5 mm in diameter were drilled in the cervical and apical regions of the buccal root surface. The teeth were randomly divided into two groups and obturated with either calcium hydroxide or calcium oxide. pH was measured in the cervical and apical wells at varying time intervals until 48 days posttreatment. After pH measurement on day 48 the vials were flushed with CO2 and the pH measured again at days 53 and 68. The results indicated a similar pattern of pH increase after treatment with either calcium oxide or calcium hydroxide. pH dropped significantly after exposure to CO2 in both groups. This study demonstrated that hydroxyl ions produced when calcium oxide reacts with water diffuse through the dentinal tubules to the surface of the root in a manner similar to hydroxyl ions from calcium hydroxide.