Does a tetnus shot cure TMJ if u already have it?

No. Tetanus shots are not used in TMJ treatment. You may be thinking about Botox or botulinum injections.
Unfortunately no.. Unfortunately ..No! TMJ is a very complex problem that can come from many different sources, but i usually see TMJ problems in people that clench or grind their teeth when sleeping (they or their spouses won't even know it). Get evaluated by a dentist to identify if this may be occurring..
No. The tetanus vaccine has no direct effect on the tmj; it stops the effects of the neurotoxin from the bacteria clostridium tetani. When present, it can cause spasm of muscles throughout the body, including the face, which is why it is called "lockjaw". Spasms of the muscles of mastication (chewing) can, however, be related to the tmj, and could benefit from muscle relaxants or TMJ therapy.