What are the causes of trigeminal neuralgia?

Several. Most commonly, there is a blood vessel that touches the trigeminal nerve and causes the covering of the nerve to wear off. This results in abnormal nerve transmission and pain. Much less commonly, there could be compression of the nerve by a mass or tumor.
Trigeminal Neuralgia. The most common form of paroxysmal orofacial pain is TN. When a demonstrable structural lesion such as a tumor (e.g., meningioma), vascular malformation or demyelinating disease (multiple sclerosis) has been identified, TN is classified as symptomatic. When the cause of TN is unknown, it is classified as idiopathic. See an orofacial pain specialist or neurologist for diagnosis and management. .
Nerve pressure. Trigeminal neuralgia is caused when an artery or vein can push on the trigeminal nerve which can cause a severe, sharp, shooting pain in the face. This pain can be a result of just gentle stroking i the face and some patients can't even brush their teeth without severe pain.
Many causes. Classic trigeminal neuralgia is typically caused by an artery compressing the trigeminal nerve at its "root entry zone". This is where the nerve changes from the central nervous system to the peripheral nervous system. However, trigeminal neuralgia type pain actually can have many other causes, such as tumor, inflammation, vascular lesions, stroke, or may not have any identifiable cause at all!