 Ninety patients with irreversible pulpitis diagnostic will participate in this clinical study. The participants will be divided into 2 groups of 45 patients, who will receive the inferior alveolar nerve block injections of 1.8 mL of 4 articaine Articaine 100; DFL, Rio de Janeiro, RJ, Brazil with 1:100,000 epinephrine or 3.6mL of the same solution. Two consecutive negative responses to the maximum pulp stimulus 80 μA at the electric pulp test were the criterion to determine a pulpal anesthesia as successful. Ten minutes after the IAN block, subjective lip anesthesia will be evaluated by asking the patient whether hisher lip was numb. Thereafter and immediately before the pulpectomy, the electric pulp stimulations will be repeated to determine pulpal anesthesia. During the pulpectomy procedure, the patients were instructed to report any painful discomfort. To evaluate the intensity of pain during the pulpectomy, a verbal analogue scale will be used. The anesthesia will be defined as successful when the dentist accessed the pulp chamber without pain being reported by the patient. In these cases, the pulpectomy will be continued. If report pain will classified the IAN block as unsuccessful. 