A New Method for the Evaluation of pH Changes in Root Dentine by Phenolphthalein Colorimetric Indicator

Objective: To analyze the effect of two different vehicles and smear layer on the diffusion of hydroxyl ions into the root dentin using phenolphthalein colorimetric indicator. Materials and Methods: Eighty-eight human mandibular premolars were used. Four randomly selected roots were used as the negative control group. The remaining roots were chemomechanical prepared and randomly divided into 2 main groups according to the final irrigation process: Group 1 (smear-): 4 mL 17% EDTA followed by 4 mL 2.5% NaOCl, group 2 (smear+): 8 mL 2.5% NaOCl. Next, 4 randomly selected roots from group 1 and group 2 were divided into 2 positive control groups. The main groups (n=38) were further divided into 2 subgroups according to the type of vehicle group 1a: CH + glycerin, group 1b: CH + distilled water, group 2a: CH + glycerin, group 2b: CH + distilled water. One week later, root canals were sectioned horizontally. Then, dentin sections were kept in 3% phenolphthalein solution for one day. The stained area, total area and root canal area were measured. The data were statistically analyzed (alpha=0.05). Results: The staining pattern was more prominent in the absence of the smear layer (p < 0.001). In the presence of the smear layer, the CH-glycerin group had more stained areas than the CH-distilled water group (p < 0.01). In the absence of the smear layer, there was no difference between the vehicles (p > 0.05). Conclusion: Both tested vehicles were effective at increasing dentinal pH. Smear layer removal may facilitate the diffusion of hydroxyl ions.