Neurovascular compression at the root entry zone accounts for more than 80% of trigeminal neuralgia (TN) cases, but not all patients with TN have neurovascular compression. Many non-TN subjects have neurovascular contract at the root entry zone. TN is reported to occur in 0.9% to 4.5% of patients with multiple sclerosis (MS). In patients with TN, 1.7% to 15% of patients suffer from MS. The reported range for patients with TN due to tumors is from 0.8% to 11.6%. Because carbamazepine may relieve pain temporarily, relief of pain with carbamazepine does not exclude the diagnosis of a tumor or cyst. There are the peripheral cause theory, central cause theory, peripheral origin central pathogenesis theory, and multiple factors theory in the pathology of TN. Dental pain and/or treatment may trigger TM. Alveolar cavitational osteonecrosis may also cause TN.