Morphological changes of infraorbital nerve by nerve block

Objectives: In our dental hospital, we have performed the nerve block by high concentration of local anesthetic on the patient with trigeminal neuralgia and acquired the good curative effect. Then, this study was planned to compare the influences on nervous tissue by the block using conventional pure alcohol with using 5% lidocaine.

Methods: 99% alcohol and 5% lidocaine were respectively injected into the infraorbital foramen of mouse, and the morphological changes of nerve injury and regeneration were observed.

Results:

1. Immediately after the injection, significant changes were not seen in both groups.

2. One day after the injection, the myelinated nerve fibers were destroyed almost completely in both groups. In alcohol group, this destruction was observed until one month after the injection, in lidocaine group, however, there was 50% reduction in the number of damaged myelinated fibers by three days after the injection.

3. In alcohol group, 3 months after the injection, 75% of the nerve fibers were less than 5µ in diameter, while 20% were the thick fibers greater than 5µ. 6 months after the injection, the thick fibers increased to 70%, while 30% were thin, which findings were very similar to those in control(saline) group.

4. In lidocaine group, from 1 week to 6 months after the injection, the percentage of thin fibers gradually decreased, while the thick fibers increased. Approximately 5% of the fibers remained destructed.

Conclusions: The results demonstrate that the thick nerve fibers increase between 3 and 6 months after the injection. This period may correspond with the time to need re-block on clinic. This correlation suggests that it takes the time for regenerative nerve fibers to grow over 5µand become functional, and furthermore, that sensory function is regained even before the thick nerve fibers returns to normal levels.