TMJ stands for temporal-mandibular joint. Temporal, as in temple area of skull; mandibular as in mandible, or lower jaw; joint as in it's where the head and jaw meet. Problems in this joint may be caused by a misalignment of the teeth, trauma, or excess muscle tension. Aside from the two bones that meet there, cartilage buffers them and five muscles are involved in the area. If something goes wrong a good deal of trouble can result. 

Problems in this area can cause:

• Headaches
• Earaches
• Trouble/soreness in opening and closing the mouth
• Clicking or popping of the jaw
• Pain in the jaw muscles
• Soreness in the area, sometimes extending to the face

Dental treatments for the condition can include replacing missing teeth, moving teeth, adjusting the bite, filling gaps between teeth, etc. There is no one solution that is right for all cases. Sometimes a plastic mouthpiece is used to prevent clenching or grinding that is contributing to the problem. If untreated and taken to extremes, surgery may be required to repair a badly damaged joint.