Comparative study on anesthetic potency depending on concentrations of lidocaine and epinephrine: assessment of dental local anesthetics using the jaw-opening reflex.

Anesthetic potency of a local anesthetic on the dental pulp was investigated by increasing or decreasing the concentration of lidocaine and that of epinephrine. An electromyogram of the digastric muscle in Japan White male rabbits was recorded during the jaw-opening reflex induced by electrical stimulation of the dental pulp. Probit analysis was used for the determination of the 50% effective volume (ED50) values of the anesthetic. The anesthetics used were plain 2% lidocaine solution (2Lid-0 group), 2% lidocaine solution with 12.5 microgram/mL of epinephrine (2Lid-1/8 group), 2% lidocaine solution with 6.25 microgram/mL of epinephrine (2Lid-1/16 group), and 4% lidocaine solution with 5 microgram/mL of epinephrine (4Lid-1/20 group). No anesthetic effect was shown in the 2Lid-0 group. The 2Lid-1/8 group indicated adequate anesthetic potency with the smallest dosage at all observation periods. The potency in the 2Lid-1/16 group was 0.3-0.5 times, and that in the 4Lid-1/20 group was 0.3-0.4 times as much as the 2Lid-1/8 group. The decrease in epinephrine concentration produced the decrease in the anesthetic potency on the dental pulp independent of lidocaine concentration. These results suggest that the increase in lidocaine concentration may not compensate the decrease in epinephrine concentration.