48 volunteers (20-31 years) were evaluated to estimate the occurrence of positive aspiration during intraceptal anesthesia, comparing it with the level of pain threshold in target tooth. Intraceptal anesthesia of lower premolars was introduced by single injection of 0.4 ml 4% articaine with 1:100,000 epinephrine by computer syringe of QuickSleeper. Each injection was monitored by electrotest before and after 1-2, 5, 10 and 15 min. At the same time the monitoring of blood pressure and heart rate was performing.