Action of adrenaline on the effect of dental local anaesthetic solutions

This study investigated the effects of dental local anaesthetic solutions containing either 2% plain lignocaine or 2% lignocaine with 1:80,000 adrenaline. The duration of anaesthesia and the occurrence of a reduction in blood flow together with its duration were examined in the dental pulps of maxillary central incisor teeth in 10 human subjects. The local anaesthetic solution was injected into the soft tissues adjacent to the apex of the sound maxillary incisor tooth. The blood flow in the dental pulp was assessed by a laser Doppler flowmeter, and the effectiveness of pulpal anaesthesia was determined by an electric pulp tester, both at timed intervals. The injection of 1-2 ml of 2% plain lignocaine had no significant effect on blood flow in the pulp of the incisor tooth in eight of 10 subjects. In the other two, there was a small but significant increase. The duration of pulpal anaesthesia was 25.1 min (SD 6.23). Following injection of 1 ml of 2% lignocaine with 1:80,000 adrenaline, there was a significant reduction (31%) of pulpal blood flow in every subject (p < 0.05). The duration of reduced blood flow was 68.5 min (SD 9.73). The duration of pulpal anaesthesia was 100 min (SD 15.09), four times the duration of anaesthesia induced by plain lignocaine. The anaesthetic solution with vasoconstrictor produced far longer anaesthesia more consistently at a lower dose than the plain solution.