 Methodology Ninety patients with single rootcanal and non-vital pulps were included. The patients were assigned into 3 groups according to root canal instrumentation technique used; the modified step-back stainless-steel hand files, HF, reciprocal WaveOne, WO, and rotational ProTaper Next, PTN. Root canal treatment was carried out in a single visit and the severity of postoperative pain was assessed by 4-point pain intensity scale. All the participants were called through phone at 12, 24 and 48 h to obtain the pain scores. Data were analyzed by the Kruskal-Wallis test. 