Causes

The causes of temporomandibular joint disorder (TMD) are not clearly understood. Most medical experts believe that TMD results when several factors act together. The following factors may cause TMD symptoms to begin, to become worse and/or to last longer.

Trauma to your jaw can occur from a blow, whiplash, jaw dislocation or compression. It can be caused by opening your jaw too wide and over-stretching it.
Disc displacement occurs when the disc in the TMJ slips out of its normal place. This is also referred to as “internal derangement.” Learn more about disc displacement.
Bad habits include bruxism, jaw grinding, lip and fingernail biting. Other bad habits are gum chewing and creating downward pressure by resting your jaw on your hands while your elbows are propped on a table.
Dental occlusion or “the bite” refers to the way your upper teeth fit together and line up with your lower teeth. In the past, dentists believed that an abnormal bite (malocclusion) could cause TMD. However, recent research studies have shown that most people with TMD have a normal bite. They also show that most people with malocclusion do not have TMD.
Depression, anxiety and increased stress can influence how severe your TMD symptoms are and how long they may last.
Joint disease such as arthritis can harm the cartilage in the TMJ. Parkinson's disease, myasthenia gravis, stroke and amyotrophic lateral sclerosis (Lou Gehrig's disease) may lead to excess or uncontrolled jaw movements.

Drug abuse and use of certain prescription medicines can affect the nerves and muscles around the jaw and can contribute to TMD.