Inferior alveolar nerve

The inferior alveolar nerves supply sensation to the lower teeth,[2]^: 519 and, via the mental nerve, sensation to the chin and lower lip.^{[citation needed]}

The

Rarely, a bifid inferior alveolar nerve may be present, in which case a second mandibular foramen, more inferiorly placed, exists and can be detected by noting a doubled mandibular canal on a radiograph.[4]

Clinical significance

Injury

Inferior nerve injury most commonly occurs during surgery including wisdom tooth, dental implant placement in the mandible, root canal treatment where tooth roots are close to the nerve canal in the mandible, deep dental local anaesthetic injections or orthognathic surgery. Trauma and related mandibular fractures are also often related to inferior alveolar nerve injuries.

Trigeminal sensory nerve injuries are associated with numbness, pain, altered sensation and usually a combination of all three.^[5] This can result in a significant reduction in quality of life with functional difficulties and psychological impact.^[6]

The risk associated with wisdom tooth surgery is commonly accepted to be 2% temporary and 0.2% permanent. However, this risk assessment is not concrete as the same source^{[citation needed]} is cited for lingual nerve paresthesia. It is well documented that inferior alveolar nerve injury is more common than lingual nerve injury.^{[citation needed]} The percentage of injury varies significantly in different studies. Furthermore, many factors affect the incidence of nerve injury. For example, the incidence of nerve injury in teens removing third molars is much lower than the incidence in patients 25 and older.^[7] This risk increases 10 fold if the tooth is close to the inferior dental canal containing the inferior alveolar nerve (as judged on a dental radiograph).^[8] These high risk wisdom teeth can be further assessed using cone beam CT imaging to assess and plan surgery to minimise nerve injury by careful extraction or undertaking a coronectomy procedure in healthy patients with healthy teeth.^[9]

The risk of nerve injury in relation to mandibular dental implants is not known but it is a recognised risk requiring the patient to be warned.^[10] If an injury occurs urgent treatment is required. The risk nerve injury in relation deep dental injections has a risk of injury in approximately 1:14,000 with 25% of these remaining persistent.^{[citation needed]} Routine preoperative warnings about these injuries should occur before surgery, and represent good practice.^[11][12] Inferior alveolar nerve injury secondary to orthodontic treatment is also emerging in the literature in the recent years as a rare complication and manifested as anesthesia, paresthesia, or combination of both; however full recovery was achieved in all of the reported cases when proper management was applied. ^[13]

Anesthesia

During dental procedures, a local nerve block may be applied. Anaesthetic injected near the mandibular foramen to block the inferior alveolar nerve and the nearby lingual nerve (supplying the tongue). This causes loss of sensation on the same side as the block to:

• the
  teeth
  (inferior alveolar nerve block)
• the
  lower lip
  and chin (mental nerve block)
• front two-thirds of the tongue (lingual nerve block).

Studies found that oral medications of

• 
  Mandible of human embryo 95 mm long. Inner aspect. Nuclei of cartilage stippled.
• 
  Mandibular division of trifacial nerve, seen from the middle line.
• 
  Inferior alveolar nerve
• 
  Mandibular nerve and bone. Deep dissection. Anterior view.
• 
  Infratemporal fossa. Lingual and inferior alveolar nerve. Deep dissection. Anterolateral view

References