Calcium concentration and pH of the periapical environment after applying calcium hydroxide into root canals in vitro

The purpose of the present study was to determine both calcium concentratio n and pH in the periapical region after application of 1 of 4 different cal cium hydroxide preparations into experimental root canals. Fifty root canal models were divided into five groups: group 1- calcium hydroxide was mixed with distilled water at a powder/water weight ratio of 38%; group 2- calci um hydroxide was mixed with distilled water at 44%; group 3- calcium hydrox ide was mixed with distilled water at 50%; group 1- calcium hydroxide powde r only was used; and group 5 - the control group, in which nothing was appl ied to the canals. All samples were immersed in distilled water maintained at 37 degreesC. Calcium concentration and pH of the distilled water were me asured after 3 days, 7 days, and then at weekly intervals up to 15 wk, duri ng which time the storage medium was renewed after each measurement. Calciu m concentration and the change in pH of the distilled water were statistica lly quicker and greater in groups 1 to 3 (mixture groups) than group 4 (pow der only) (p < 0.05). The highest calcium concentration (peak Ca2+ release) was observed after 3 days for the mixture groups, whereas that for the pow der only group was found at 7 days. Peak pH change was found after 14 days for the mixture groups, whereas that for the powder only group was found at 49 days. After peaking, all groups showed a decline of the pH over time. T hese results suggest that the time required for optimum intracanal activity when using calcium hydroxide mixtures is at least 2 wk.