The recommended minimum or optimal apical size of canal preparation is size 25. All the operators are informed to perform the endodontic treatment the way operators normally do. The only variation during treatment was the concentration of the sodium hypochlorite solution for irrigation of the root canal. One group was irrigated with Sodium Hypochlorite 0.5 % (Dakin's solution) and the other group with Sodium Hypochlorite 3 %.