 Ninety patients will Participate in this clinical study. The patients will be admitted to the Emergency Center of the School of Dentistry at the University of São Paulo with a clinical diagnosis of irreversible pulpitis, The study was approved by the Committee on the Ethics of Research on Human Beings of the School of Dentistry at the University of São Paulo protocol 9507, and each patient will be informed to sing consent to participate in the study. The 90 participants will be divided into 2 groups of 45 patients, who will receive the inferior alveolar nerve block injections of 1.8 mL equivalent to 1 cartridge of 4 articaine Articaine 100; DFL, Rio de Janeiro, RJ, Brazil with 1:100,000 epinephrine or 3.6mL equivalent to 2 cartridges of the same solution. Two consecutive negative responses to the maximum pulp stimulus 80 μA at the electric stimulation were the criterion to determine a pulpal anesthesia as successful. Before the IAN block injections, the tooth with irreversible pulpitis, the adjacent tooth, and the contralateral canine will be tested for pulp vitality with an electric pulp test Vitality Scanner 2006; SybronEndo, Orange, CA. The electric pulp stimulation of the contralateral canine, which will be not anesthetized, will be used as control to ensure that the equipment is working properly and that patients is responding adequately. 