The lingual nerve (LN) is a branch of the mandibular division of the trigeminal nerve, which is formed from afferent branches from the body of the tongue that travel along the lateral surface of the tongue [1]. Injury to the LN may cause significant patient morbidity and is one of the leading causes of litigation in dentistry and oral and maxillofacial surgery. Injury to the LN can occur during a multitude of surgical procedures including third molar extraction, local anesthetic injections, preprosthetic surgery, placement of dental endosseous implants, orthognathic surgery, excision of maxillofacial pathology, and penetrating trauma to the floor of mouth and tongue. There have also been infrequent reports of LN injury secondary to laryngoscopy for intubation and placement of a laryngeal mask airway [2, 3]. The vast majority of LN injuries that are routinely seen by trigeminal nerve microsurgical specialists are those that are iatrogenic in nature occurring with mandibular third molar extractions and dentoalveolar surgery. During mandibular third molar surgery, the LN is not generally visualized intraoperatively and is usually protected through the judicious placement of incisions and subperiosteal plane flap elevation. With anatomical aberrancy, iatrogenic injury to the LN can occur even in the most skilled surgeon’s hands. Injury to the LN can occur in situations where the nerve is located in a “high-risk” position, namely, at or above the level of the lingual crest or medial and contiguous with the lingual cortical plate (Fig. 13.1) [4]. Numerous anatomic studies have reported on the variable position of the LN with regard to third molar extraction. In a study by Pogrel and colleagues, the LN was located above the lingual crest in 15 % of cadavers within a 3.45 mm mean horizontal distance from the lingual crest in the third molar region [5]. Miloro and colleagues using magnetic resonance imaging (MRI) identified the LN above the lingual alveolar crest in about 10 % of specimens, and in direct contact with the lingual plate in approximately 25 % of specimens [6]. Therefore, medially directed crestal incisions, fractures, or perforations of the lingual cortex, aggressive dissection, and curettage on the medial tissues of the surgical site can all potentially result in an LN injury [4]. A frequently cited study using a questionnaire reported that LN injuries occur in 11 % of cases involving the removal of a mandibular third molar [7]. In these cases, the authors reported that approximately 50 % of patients made full neurosensory recovery within 36 weeks, and all but 6 (0.5 %) of the cases ultimately recovered sensation. There is a wide range of LN injury incidence reported in the literature, dependent upon varying measurements and classifications of injury utilized. Unfortunately, most of the past literature has been retrospective in nature with no standardization in measuring sensory levels until more recent publications utilizing the British Medical Research Council (MRC) scale [8]. The British MRC scale was developed for grading sensation subsequent to peripheral nerve injuries since neurosensory function cannot be assessed directly [8–10]. This scale takes into account the sensations of vibration, pinprick, light touch, two-point discrimination, and temperature and is ranked on scale of S0–S4 (functional sensory recovery defined as greater than S3).
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