Inferior alveolar nerve injury

Last revised by Rohit Sharma on 26 Feb 2023

Inferior alveolar nerve injuries are most commonly iatrogenic, predominantly post third mandibular molar extraction, although they can occur post dental implant. Mandibular fractures are the most frequent non-iatrogenic etiology. This article is focussed on iatrogenic injuries. 

The incidence of injuries to the inferior alveolar nerve after third mandibular molar extraction is reported to be ~7% (range 0.4-13.4%) 1

Patients may complain of paresthesia of the lower lip and chin (i.e. numb chin syndrome) 1

There are radiographic-identifiable features of the mandibular canal (which contains the inferior alveolar nerve) that place the patient at higher risk of inferior alveolar nerve injuries (although there are other. CT/CBCT allows for more accurate delineation of the relationship than OPG. 

On OPG, the proximity of the third mandibular roots to the mandibular canal is a risk factor, with a higher risk of inferior alveolar nerve injury with an intimate relationship 2:

  • distant: ≥1 mm between the root tips and the mandibular canal

  • close: superimposition of the root tips over the mandibular canal

  • intimate (≥1 of the following)

    • mandibular canal diversion

    • darkening of the root

    • root apices deviation

In addition to an intimate relationship, interruption of the white line of the mandibular canal has been shown to be risk factors on OPG 3

The presence of a close or intimate relationship of the mandibular canal with the third mandibular molar roots on OPG may necessitate further evaluation with CT or cone-beam CT. Factors on the coronal plane that increase the risk of inferior alveolar nerve injury include 1:

  • direct contact of the mandibular canal and roots

  • buccal or lingual position of the mandibular canal compared to the roots

  • teardrop or dumbbell shape to the mandibular canal

  • absence of mandibular canal cortication

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