Electric pulp test is a method to examine the vitality of dental pulp using the electrical stimulation. During the pulp test, the current stimulates intradental nerve, and give severe pain to patients. Some studies were accomplished to measure the responses of subjects by stimulating over the sensory threshold. But these studies were focused on the time delay of subject's response after stimulating over the threshold. The purpose of this study was first to measure the excessive stimulation time during pulp testing by means of EMG in anterior belly of digastric muscle, voice, and finger movement, secondly, to determine whether the excessive stimulation time could be reduced by the specially designed automatic circuit breaker on the basis of EMG signal.