The inferior and lingual alveolar nerves are vital anatomical structures potentially at risk of injury during some oral surgery procedures, such as the removal of wisdom teeth or the insertion of dental implants and, albeit not frequently, also during nerve block techniques.
In the case of accidental injuries, there are several classification criteria useful to describe the extent of the damage. Conceptually, there are interruption injuries (corresponding to 1st to 3rd degree according to Sunderland), separation of the pereineurium with an intact epineurium (Sunderland 4th degree) or interruption of the entire nerve (Sunderland 5th degree).
One of the reasons underlying the risk of iatrogenic injury consists of the anatomical variability to which the course of the two nerves is subject. As far as the lower alveolar nerve is concerned, the same reason constitutes one of the possible contributing factors underlying the high failure rates of conventional nerve block techniques.
The use of radiological imaging techniques allows for an evaluation of the anatomical picture. Moreover, the execution of tests such as cone beam CT scan is mandatory in the framework of traumatic events; for example following needle breakage during local anesthesia.
Nevertheless, CT and cone beam CT scans are not able to directly display the nerve structure, but only show the hypodense images relative to the course of the mandibular canal. The diagnostic potential of other diagnostic tests, therefore, should be assessed.
Electroneurography or somatosensory evoked potentials are commonly accompanied by a basic neurological examination in the first post-traumatic and possibly post-surgical phase, during which they are usually repeated several times.
Recently, the use of new, dedicated nuclear magnetic resonance sequences has provided positive results in the direct, high-resolution visualization of the inferior alveolar nerve and lingual nerve (course and possible variations). The technology could be implemented through the development of quantitative biomarkers, useful for confirmation or rejection of a suspected interruption of nerve structure conduction.
Said indications were recently confirmed by a study on a sample of 30 healthy subjects, conducted by Burian and colleagues and published in Clinical Oral Investigations. The mandibular nerve first, then the lower alveolar nerve were traced from the oval foramen up to the mental foramen, while the lingual nerve was visible with high precision close to the oral floor in the third molar region. The STIR (Short Tau Inversion Recovery sequence showed the maximum contrast of nerve structures compared to muscle tissue. It was also possible to differentiate the tissue composition of the vascular nerve bundle within the mandibular canal.
The study outlined the potential of nuclear magnetic resonance in the direct study of the inferior and lingual alveolar nerves. This method is therefore suitable for the evaluation of such structures in complex surgical cases, or in the evaluation of traumatic events.