TMJ disorders are linked to tinnitus because of the nerves that run near it. In my case, if I force an underbite I can make both of my ears ring but I don't have any TMJ issues.

There are some physical therapists (also dentists) that focus on maxillofacial dysfunction and TMJ disorders, so that's an avenue to go down as well.

The other two common reasons for tinnitus:

* Hearing damage (gunshots, explosions, etc.) and those are not reversible as of yet

* Ototoxic drugs. When I last did research on it it years ago, like hearing damage from gunshots, was also irreversible.