Neurosensory risk and 3rd molar: identifying the real predictors

The extraction of impacted mandibular third molars is a surgical routine which, despite its predictability, carries the risk of dreaded neurosensory complications: lesions of the inferior alveolar nerve (IAN) and the lingual nerve (LN). While the majority of these injuries resolve spontaneously, their potential impact on mastication, speech, and quality of life necessitates rigorous preoperative risk stratification. The challenge for the practitioner lies in the heterogeneity of contributing factors — anatomical, radiographic, and technical — whose actual influence often remains debated.

This retrospective cohort study, analyzing 165 mandibular molars extracted between 2021 and 2023, aimed to clarify these uncertainties. The primary objective was to determine the precise incidence of neurosensory deficits (combined IAN and LN) and to isolate independent predictors of these complications through multivariate analysis. The authors specifically tested the influence of key variables such as radiographic overlap with the mandibular canal, impaction depth (Pell & Gregory), root morphology, and operative duration (30-minute threshold). The clinical challenge is direct: to refine informed consent and optimize therapeutic decision-making, particularly regarding coronectomy, for high-risk patients.

Study methodology

This retrospective cohort study was conducted within the department of oral and maxillofacial surgery at the Geetanjali Dental Institute (India). It is based on the analysis of clinical and radiographic records of patients operated on between January 2021 and April 2023.

• Sampling: The sample size was calculated a priori to ensure a statistical power of 80%. Based on an estimated prevalence of 7.2% for nerve lesions, a target of 165 impacted mandibular third molars was set.
• Inclusion criteria: The study included adult patients (≥ 18 years) with complete surgical records and dental panoramic radiographs. Patients with a history of mandibular fractures, pathologies associated with impacted teeth, or pre-existing nerve dysfunctions were excluded.
• Neurosensory evaluation: The primary endpoint was the occurrence of inferior alveolar nerve (IAN) or lingual nerve (LN) injuries. Postoperative clinical examinations allowed for the classification of injuries as transient or permanent (persistence of symptoms beyond 6 months).
• Radiographic and operative analysis: The parameters studied included the depth of impaction and the relationship with the ascending ramus (Pell and Gregory classification), root overlap with the alveolar canal, as well as surgical variables such as the extent of the osteotomy and the performance of a coronectomy.
• Reliability and statistics: The reproducibility of radiographic interpretation was confirmed by a high Cohen's kappa coefficient (0.89 inter-examiner). Multivariate analysis models were applied to identify independent predictors of neurosensory complications.

Incidence and characteristics of neurosensory lesions

In a cohort of 135 patients totaling 165 impacted mandibular third molars, the study reports an overall incidence of postoperative neurosensory disturbances of 7.3% (n=12). These complications are divided into 5.5% transient lesions (n=9) and 1.8% permanent lesions (n=3), defined by the persistence of symptoms beyond six months.

The demographic profile shows a mean age of 28.4 ± 8.2 years with a majority of female patients (63.0%). Anatomically, 36.4% of the molars showed radiographic overlap with the inferior alveolar canal. The analysis of surgical complexity reveals that 36.4% of the procedures lasted more than 30 minutes.

Morphological analysis shows that mesio-angular impactions are the most frequent (30.3%), followed by disto-angular (27.3%) and vertical (24.2%). Regarding the depth of impaction according to Pell and Gregory, Class B predominates (42.5%), ahead of Class C (33.3%) and Class A (24.2%). The space available at the ramus level was considered adequate (Class I) in 51.5% of cases.

The reproducibility of the radiographic interpretation was validated by an excellent Cohen's kappa coefficient, reaching 0.89 for inter-examiner agreement and 0.92 for intra-examiner agreement, ensuring the reliability of the reported canal proximity data.

Clinical analysis and neurosensory risk management

This retrospective study, involving 165 mandibular third molar extractions, reports a 7.3% incidence of neurosensory complications. This figure, although comparable to standard data in oral surgery, highlights the persistence of a significant risk. While 5.5% of cases are transient, the permanent lesion rate (1.8%) should encourage increased vigilance during planning.

Nerve injuries in 3rd molar surgery: figures for your practice

Cette étude rétrospective menée sur 165 extractions de troisièmes molaires mandibulaires rapporte une incidence de complications neurosensorielles de 7,3 %. Fait rassurant : la grande majorité des lésions (5,5 %) sont transitoires, tandis que le risque de séquelles permanentes reste limité à 1,8 %. Les données identifient le chevauchement radiographique radiculaire avec le canal alvéolaire (présent dans 36,4 % des cas) et une durée opératoire supérieure à 30 minutes comme les variables critiques influençant ce pronostic.

In concrete terms, for the practitioner:

• Monitor the stopwatch: A procedure exceeding 30 minutes significantly increases the risk of trauma. In the case of deep impaction (Class C), if the extraction appears laborious, coronectomy remains a prudent alternative to preserve the inferior alveolar nerve.
• Target the overlap: The radiographic sign of overlap on the panoramic view is a reliable predictor of anatomical proximity. In these cases, reinforced preoperative information regarding the risk of paresthesia is essential for your medico-legal protection.
• Optimize follow-up: 75% of neurosensory disorders resolve spontaneously within 6 months; monthly follow-up allows monitoring of recovery and reassures the patient about the transient nature of the impairment.

Technical lexicon of the study

Pell and Gregory Classification: Radiographic evaluation system used in the study to categorize the depth of impaction (Classes A, B, C) and the spatial relationship of the tooth with the mandibular ramus (Classes I, II, III).

Coronectomy: Alternative surgical procedure consisting of removing the crown of an impacted molar while leaving its roots in place to protect the inferior alveolar nerve.

Alveolar osteitis: Post-operative complication mentioned, commonly known as dry socket, characterized by painful inflammation of the alveolar bone after extraction.

Dysesthesia: Alteration of tactile sensitivity manifesting as abnormal, distressing, or even painful sensations, used as a diagnostic criterion for nerve injury.

Paresthesia: Subjective sensitivity disorder (tingling, numbness) reported during clinical follow-up to evaluate damage to the inferior alveolar or lingual nerves.

Hypoesthesia: Decrease in normal sensitivity (partial anesthesia) identified during objective neurosensory examinations conducted during the post-operative follow-up period.

Information intended for healthcare professionals. This content may contain errors or truncated summaries. We recommend always verifying with the original source article. Delynov disclaims all responsibility for the use of this information. This document is not intended for patients or the general public.