On and off for years i've had problems with the left side of my jaw. it locks up and clicks. why do i get this and how can i treat it?

TMJ: Sounds like this could be TMJ disease. You may want to mention to your dentist or doctor. Things can be done depending on severity.

Dislocated disc : The most frequent cause of the symptoms you are having is a dislocated disc or meniscus in the jaw joint. The most conservative treatment is to have a bite appliance made to reduce the frequency of the click, and to try to prevent your jaw from locking. The diagnosis is confirmed by a MRI of the tm joints. You should consult an oral surgeon in your area.

TMJ: TMJ. See TMJ specialist. Any dentist can be a TMJ expert with the proper training and experience. Most commonly, oral surgeons, prosthodontists, and orofacial pain specialists. Ask your MD, your dentist and your dental society for referrals.