Methods: Thirty human mandibular premolars were root canal treated and randomly divided into three groups. Bleaching agents were placed into the pulp chambers and renewed every 7 days. The process was repeated 3 times. Group 1: sodium perborate mixed with water, group 2: sodium perborate mixed with 30% hydrogen peroxide, group 3: distilled water (control group). Access cavities were sealed and the teeth were stored in distilled water at room temperature. After the bleaching procedure, teeth were sectioned at the cemento-enamel junction level and Vickers microhardness testing was carried out on dentin surface at two different positions: inner and outer dentin. Microhardness data was analysed using Kruskal Wallis and Wilcosxon signed-rank to compare between the 3 groups. Results: There was no significant difference in dentin microhardness between the 3 groups (p>0.05).
Conclusions: Intracoronal bleaching with sodium perborate mixed with water or 30% hydrogen peroxide did not alter the microhardness of dentin.