Methods: 60 extracted mandibular molars were selected, randomly divided into 3 groups: (1sf) treated with 10% CP (Nupro Gold 10%, Denstply) for 40 hours; (2nd) treated with 10% CPfor 40 hours and followed by immersing in distilled water for 72 hours and (3rd) untreated, preserved in distilled water (controlgroup).