Pain upon opening the mouth can be a symptom of temporomandibular joint disorder, or TMD, according to WebMD. This common condition is also called TMJ, though that acronym more accurately refers to the jaw joint itself.
The temporomandibular joint connects the jaw to the temporal bones of the skull, according to WebMD. It is a hinge joint that allows the jaw to move up and down as well as side to side. Problems with the joint and the facial muscles that control it are thought to cause discomfort and other associated symptoms.
Other symptoms of TMD include head, neck, facial and ear pain; headaches; a jaw that pops, grinds or clicks when opening the mouth or chewing; swelling on the affected side; and a jaw that locks into position or is difficult to open, says eMedicineHealth.
Trauma, such as a blow to the jaw or injury due to a car accident, as well as damage that occurs due to jaw clenching or teeth grinding, are common causes of TMD, notes eMedicineHealth. So are osteoarthritis and rheumatoid arthritis.
Treatment of TMD includes the use of ice, heat and gentle massage to relax the muscles around the joint; eating soft foods; and utilizing over-the-counter NSAIDS, such as ibuprofen, to reduce inflammation, states the Cleveland Clinic. Muscle relaxers and anti-anxiety medications may be suggested. A mouth guard or splint may also be prescribed. Ultrasound, radio and TENS therapy can also help. Surgery is a last resort.