Trauma that causes facial nerve paralysis generally occurs in one of two locations:

Intracranial Trauma
(Trauma within the skull)

The facial nerve courses through the temporal bone between where the nerve leaves the brainstem and where it exits the skull and enters the face. Any trauma strong enough to cause a fracture of this temporal bone may cause facial nerve paralysis.

This is often seen after motor vehicle accidents or blast injuries and is more common in adults, although it may occur in children. If the paralysis occurs immediately after the accident, surgery involving decompression of the nerve via the skull base is performed by neurosurgeons and otolaryngologists.

Close monitoring of the condition, rather than active treatment, is chosen when the paralysis progresses slowly. 

Extracranial/Facial Trauma

This type of injury is most commonly penetrating, either from a knife cut or projectile. Dental procedures or nerve blocks rarely cause this type of injury.

Recovery can sometimes be seen without surgical intervention if the injury is close to the middle of the face, where the nerve branches are very small but also interconnect with other branches. If the injury is more to the side of the face, surgical repair of the nerve is usually needed, preferably within the first 72 hours of injury.

The decision whether to repair the nerve and the choice of surgical technique is usually done by an experienced plastic and reconstructive surgeon who has advanced training in facial nerve surgery and microsurgery.