An Experimental Study on the Electrophysiological Evaluation of Nerve Function in Inferior Alveolar Nerve Injury -The Relationship between Nerve Action Potentials and Histomorphometric Observations-

Statement of the problem

Inferior alveolar nerve (IAN) injury is common in the field of general practice of dentistry oral and maxillofacial surgery.In order to understand the symptoms associated with IAN injury, subjective symptoms are recorded and sensory tests are used (ex: Frey tactile stimulation, 2-point discrimination, pinprick, temperature test, Semmes Weinstein pressure aethesiometer (SW Test). Unfortunately, these evaluations are determined by what the patients declare and its subjective nature makes the accurate diagnosis of nerve injury very difficult. There are cases where procedures such as nerve grafting or nerve repair surgery cannot take place due to the uncertainty of the evaluation. In other more severe cases where follow-up treatment instead of surgical procedure was undertaken after subjective evaluation, dysaesthesia occurred as neurological sequelae. Electrophysiological nerve function evaluation using sensory nerve action potential (SNAP) is important for the diagnosis and treatment of nerve injuries.The objective of this study is to improve the accuracy of nerve injury diagnosis by determining the degree of damage using SNAP and the sensory nerve conduction velocity (SCV).

Materials and methods

Adult male rabbits weighing 2.5kg (n=33) were prepared. Crush, partial and complete nerve amputation injuries were applied to the IAN of rabbits then SNAP and histomorphometric observations were recorded at 1, 5 and 10 weeks.

Results

For crush injury, most nerves were smaller in diameter at 5 weeks than at 1, however after 10 weeks, extensive nerve regeneration was observed. SNAP shows a decrease in SCV at week 1 and 5 followed by an increase at week 10. For partial nerve amputation, small to medium sized nerve fibers were observed at week 1 and 5 then larger nerves were seen at week 10. Minimal changes in SCV were observed at week 1 and 5 however SCV increased at week 10. For complete nerve amputation, nerve fibers were sparse at week 1 but gradual nerve regeneration was observed from week 5 and 10. SNAP was detectable from week 10 however SCV was extremely low.

Conclusion

In this experiment, histomorphometric observations and SNAP of nerve injuries were compared and characteristics were periodically examined. In terms of diagnosis, complete nerve amputation is an injury that can be diagnosed at the earliest time. Crush injury and partial nerve amputation can be diagnosed after a minimum of 10 weeks of observation. This study proves that SCV is an effective factor in the evaluation of nerve injury and regeneration.