Comparison of infradental nerve response to inflamed pulp after local application of Lidocaine and Lidocaine plus Morphine in cats

Failure to obtain adequate anesthesia in teeth with inflamed pulps has been known as a clinical symptom for dentists. The aim of this study was to determine the infra-alveolar nerve response to supplementary injected morphine to Lidocaine in anesthetizing teeth with inflamed pulps. Thirty mandibular canine in 15 cats were exposed in order to become inflamed. The inferior alveolar nerve was exposed and the recording electrodes were placed upon it while the stimulating electrodes were placed on the teeth. By stimulating the teeth using the stimulator in different voltages, all the received nervous responses were recorded by means of an oscilloscope unit. If the fibers were not blocked a Lidocaine injection, supplementary injection with morphine was used and responses were recorded again. The data were analyzed by t- test. In teeth with inflamed pulps both morphine and/or Lidocaine had significant local anesthetic effects. Lidocaine and morphine acted quite similar and blocked the second group (c) fibers more rapidly and strongly than the first group (A delta) fibers. Supplementary injection of morphine in those cases in which Lidocaine failed to block the first group fibers raised the stimulation threshold and decreased the wave peak and the speed of the first group fibers (p>0.05). Pulpal nerves received morphinergic receptors during inflammation and resisted to the Lidocaine and became anesthetized after supplementary injection of morphine. Using morphine as an adjunct to Lidocaine may complete the anesthetic effect on neurons in inflamed pulps.