Lingual Nerve Injury in Third Molar Surgery: Prevention

The removal of mandibular third molars is among the most common operations in oral and maxillofacial surgery, and it carries a small but serious risk of damage to the lingual nerve. Injury to this nerve is disabling out of proportion to its frequency, because it produces numbness, altered taste, ...

The removal of mandibular third molars is among the most common operations in oral and maxillofacial surgery, and it carries a small but serious risk of damage to the lingual nerve. Injury to this nerve is disabling out of proportion to its frequency, because it produces numbness, altered taste, and sometimes painful dysesthesia of the tongue, and unlike some surgical complications it can be permanent. This article reviews the anatomy of the lingual nerve and the operative precautions that keep the injury rate low.

The Anatomy of Risk

The Course of the Lingual Nerve

The lingual nerve is a branch of the mandibular division of the trigeminal nerve that descends medial to the mandibular ramus, and descends into the floor of the mouth, where it supplies the ipsilateral two-thirds of the tongue, the gingiva, and the sublingual structures. It also carries the chorda tympani fibers responsible for taste from the anterior tongue. In the third molar region the nerve lies in the lingual soft tissue, and its position is variable: it can lie above the crest of the ridge, close to the lingual plate, and an intimate relationship with the lower third molar root is seen in a minority of dissections.

Risk Factors for Injury

The reported incidence of temporary lingual nerve disturbance after third molar surgery ranges from less than 1 percent to over 20 percent, while permanent injury is rare, of the order of 0.1 to 0.5 percent. The risk is influenced by the depth and angulation of the impaction and by the surgical technique, and there is consistent evidence that the lingual retraction of the flap and the use of rotary instruments in the lingual region increase the danger. The surgeon's experience also matters.

Surgical Prevention

Flap Design and Reflection

The most common injury mechanism is a lingual retractor that displaces and stretches the nerve; the buccal approach is therefore used whenever access permits. Where the tooth is buccally positioned or access is adequate, the lingual tissue is left undisturbed, and where a lingual flap is necessary, the retractor is placed on the bone margin, with the periosteum and the nerve displaced as a single unit, and is kept in place for the minimum time with the minimum force. Studies confirm that lingual nerve injury falls sharply when routine reflection is omitted.

Lingual Retraction as the Decisive Step

When lingual access is unavoidable, the retraction must be executed deliberately. The periosteal elevator is inserted through an incision at the disto-buccal angle, the lingual soft tissue is peeled from the bone in one continuous detachment, and the retractor is seated firmly on the lingual cortex so that the blade lies on bone and the nerve, attached to the periosteum, is carried lingually out of the field. The retractor is never rocked, its position is checked as the bone removal proceeds, and the assistant must not readjust it blindly, because a retractor that slips onto the nerve is a common cause of damage. Every cut should be made knowing exactly where the retractor lies.

The Use of Rotatory Instruments and Sectioning

The cutting instruments are the second hazard. The bur should only engage tissue on the buccal and occlusal aspects of the tooth, and bone removal on the lingual side is kept to the minimum necessary, because a socket opened lingually brings the nerve into the field of the rotating instrument. When the tooth is sectioned, the bur is directed buccally and away from the lingual plate, and controlled, intermittent cutting prevents both the soft-tissue and the heat injury that a heavy-handed pass can cause. Sharp elevators used to luxate the roots are directed buccally as well, since a slip lingually can lacerate the nerve.

Antibiotics, Technique, and the Management of Difficult Cases

Case selection is decisive. A deeply impacted and lingually displaced third molar carries the highest risk, and in such a case the surgeon weighs the indications for removal against the danger to the nerve, obtaining explicit consent and considering whether to retain, expose, or refer the tooth. Prophylactic measures such as corticosteroids and antibiotics address swelling and infection rather than nerve injury directly, while a shorter, simpler operation is itself protective.

When Injury Occurs

Assessment and Documentation

Despite all precautions, a postoperative sensory disturbance occasionally develops. The clinician notes the subjective symptoms, the distribution of the numbness, and the effect on taste, and charts the deficit with a reproducible baseline so that recovery can be followed. The patient is reassured that most lingual nerve injuries are temporary and recover within weeks to months, and is told to protect the affected area from burns and self-injury.

Observation and the Decision to Refer

The standard course for an initial disturbance is close observation, because the majority of injuries improve spontaneously. Where a complete anesthesia persists beyond three months, or where dysesthetic pain is developing, the patient is referred to a specialist with access to microneurosurgical repair. The message of this article is simple: the lingual nerve is injured by a retractor that slips, by a bur that wanders lingually, or by a flap reflected needlessly.

Clinical Key Points

- The lingual nerve is variable in position and may lie close to the third molar.

- Permanent lingual nerve injury is rare, affecting roughly one in a few hundred cases.

- The buccal-only approach and avoidance of routine lingual retraction lower the risk.

- A lingual retractor must rest on bone and be held still throughout the procedure.

- Lingual bone removal and lingual escape of the bur are the mechanical causes of damage.

- Persistent or painful deficits warrant specialist assessment and possible repair.

Conclusion

Lingual nerve injury in third molar surgery is a preventable complication when the anatomy is respected and the technique is disciplined. A sound flap plan, a retractor that is placed decisively on bone and held there, and cutting that is consciously directed away from the lingual plate together reduce the incidence to the very low level that the operation can achieve. The lingual nerve should be present in the surgeon's mental image of every lower third molar extraction, and with it in view, the tooth can be removed safely.