The lingual nerve is a sensory branch originating from the mandibular division of the trigeminal nerve. This nerve provides general sensation (touch, temperature, and pain) to the mucous membrane of the anterior two-thirds of the tongue, the floor of the mouth, and the adjacent gum tissue of the lower jaw. It also carries special sensory fibers from the facial nerve (chorda tympani) that allow for taste perception in the same region. Damage, often resulting from trauma or surgical procedures, disturbs both sensation and taste function, impacting a person’s ability to speak and eat.
Primary Causes of Lingual Nerve Damage
Lingual nerve injury is most frequently an unintended complication of surgical and dental procedures performed in the lower jaw and mouth. The nerve’s proximity to the lower third molar, or wisdom tooth, makes its extraction the most common cause of injury. During this procedure, the nerve can be directly traumatized by surgical instruments, compressed by bone fragments, or inadvertently severed.
The administration of local anesthesia, specifically the inferior alveolar nerve block, is another recognized cause of injury. Damage can occur through direct physical trauma from the needle puncturing the nerve sheath or, less commonly, through a chemical reaction from the anesthetic solution itself. Other surgical procedures involving the lower jaw also carry a risk, including the placement of dental implants in the posterior mandible, pre-prosthetic surgery, and procedures that require soft tissue manipulation on the inner side of the jaw. The nerve’s superficial position in the area near the third molar makes it particularly vulnerable to injury during any procedure requiring lingual flap retraction or surgical access to the floor of the mouth.
Symptoms and Clinical Assessment
Injury to the lingual nerve manifests in a variety of sensory disturbances. The most common subjective symptoms include paresthesia, a diminished or altered sensation often described as tingling or “pins and needles,” and anesthesia, a complete loss of sensation. Patients may also experience dysesthesia, characterized by a painful, burning, or aching sensation that occurs spontaneously or is triggered by light touch or temperature change. Because the nerve carries taste fibers, injury often results in dysgeusia (altered or reduced ability to taste) or ageusia (complete loss of taste) on the affected side of the tongue. These sensory changes can lead to functional difficulties, such as unintentional biting of the tongue or challenges with speech and chewing.
Clinical Assessment
A healthcare provider determines the extent of the damage through a detailed neurosensory examination, comparing the injured side to the unaffected side. Objective sensory testing includes using calibrated tools to assess light touch (often done with von Frey hairs) and pinprick sensation to test the patient’s response to a sharp stimulus. Two-point discrimination is a specific test where a clinician determines the shortest distance at which a patient can distinguish two separate points of contact on the tongue, providing a measurable metric for nerve function. Gustatory function tests are also performed to evaluate the patient’s ability to perceive sweet, sour, salty, and bitter tastes on the anterior two-thirds of the tongue.
Treatment Strategies and Recovery Outlook
The initial management of lingual nerve injury involves conservative observation, as many mild injuries resolve spontaneously. For minor injuries caused by compression (neuropraxia), recovery is rapid and complete. If the injury is more severe, such as axonotmesis where nerve fibers are damaged but the sheath remains intact, recovery may take six to twelve months as the nerve regenerates.
Pharmacological intervention manages symptoms and encourages healing. This includes corticosteroids or non-steroidal anti-inflammatory drugs to reduce nerve inflammation. For patients experiencing neuropathic pain, medications such as tricyclic antidepressants or anticonvulsants like Gabapentin are prescribed to control chronic discomfort.
If sensory function does not return after three months, or if the initial injury was a complete severance (neurotmesis), surgical intervention is considered. Microsurgical repair, ideally performed within six to nine months, involves procedures like neurolysis (removing scar tissue) or neurorrhaphy (directly repairing a severed nerve). If a gap exists in the nerve, a nerve graft may be used to bridge the distance. This often utilizes a decellularized cadaveric nerve graft as a scaffold to facilitate regeneration. The prognosis for recovery is influenced by the severity of the initial trauma and the time elapsed before treatment. Outcomes are generally better for patients who undergo surgical repair within the first six months.