Clinical Practice
Lingual nerve damage due to inferior alveolar nerve blocks: A possible explanation

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ABSTRACT

Background

An explanation for the predominance of injuries to lingual nerves over those to inferior alveolar nerves as a result of inferior alveolar nerve blocks may be due to the nerves' fascicular pattern. A unifascicular nerve may be injured more easily than a multifascicular nerve.

Methods

The authors unilaterally dissected lingual and inferior alveolar nerves from 12 cadavers. They cut the specimens 2 millimeters above the lingula for both the lingual nerve and inferior alveolar nerve and opposite the site of the middle of the third molar for the lingual nerve, and they counted the number of fascicles at each site.

Results

For the lingual nerve at the lingula, the mean number of fascicles was three (range, one to eight). Four of the 12 nerves (33 percent) were unifascicular at this point. Opposite the third molar, the lingual nerve had a mean of 20 fascicles (range, six to 39). In every case, there were more fascicles in the third molar region than above the lingula in the same nerve. At the lingula, the inferior alveolar nerve had a mean of 7.2 fascicles (range, three to 14).

Conclusion

This study may explain the observation that when an inferior alveolar nerve block causes permanent nerve impairment, the lingual nerve is affected about 70 percent of the time and the inferior alveolar nerve is affected only 30 percent of the time. In 33 percent of cases, the lingual nerve had only one fascicle at the lingula; a unifascicular nerve may be injured more easily than a multifascicular one.

Clinical Implications

There is no known way to avoid the remote possibility of nerve damage resulting from an inferior alveolar nerve block. The lingual nerve may be predominantly affected because of its fascicular pattern.

Section snippets

MATERIALS AND METHODS

We dissected the lingual and inferior alveolar nerves unilaterally from 12 cadavers. We dissected out the lingual nerve from approximately 5 millimeters above the lingula down to the lower second molar region. The inferior alveolar nerve was dissected out from 5 mm above the lingula to where the nerve entered the inferior alveolar canal just below the lingula. We cut and embedded the specimens 2 mm above the lingula (where a nerve block might be injected) for both the lingual nerve and inferior

RESULTS

The results of the fascicle count at each point are shown in the table (page 197).

For the lingual nerve sectioned just above the lingula, the mean number of fascicles was three (range, one to 8). Four of the 12 nerves (33 percent) were unifascicular at this point. Opposite the third molar, the lingual nerve had a mean of 20 fascicles (range, seven to 39). In every case, there were more fascicles in the third molar region than above the lingula in the same lingual nerve. This must mean that the

DISCUSSION

All studies of nerve damage resulting from inferior alveolar nerve blocks have shown a predominance of lingual nerve involvement over inferior alveolar nerve involvement, and it appears that the lingual nerve may be involved up to 70 percent of the time.2 There seems no obvious reason for this, since if needle trauma or intraneural hematoma were the cause of the problem, one would expect the distribution to be equal. If the cause of the problem was a neurotoxic effect from the local anesthetic

CONCLUSIONS

To date, there has been no explanation of the noted phenomenon that on the rare occasion that an inferior alveolar nerve block causes nerve damage, the lingual nerve is affected 70 percent of the time and the inferior alveolar nerve only 30 percent of the time. Our study demonstrates that there is a difference in the fascicular pattern of these two nerves just above the lingula where an inferior alveolar nerve block is normally deposited. At this site, the lingual nerve is unifascicular in

References (13)

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1

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Dr. Pogrel is a professor and the chairman, Department of Oral and Maxillofacial Surgery, University of California, San Francisco, Box 0440, 521 Parnassus Ave., San Francisco, Calif. 94143-0440

2

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Dr. Schmidt is an assistant professor of oral and maxillofacial surgery, Department of Oral and Maxillofacial Surgery, University of California, San Francisco.

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Dr. Sambajon is an assistant professor of clinical oral and maxillofacial surgery, Department of Oral and Maxillofacial Surgery, University of California, San Francisco.

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Dr. Jordan is an associate professor, Division of Oral Pathology, Department of Stomatology, University of California, San Francisco.

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