The bite i wear for tmj helps a lot my jaw feels nice and loose and no pain when i have it in but when i take it out and bite all the way down i get a lot of pain where the jaw joint comes together why?

Muscle pain: You may want to consider using your TMJ appliance more frequently as to relieve your pain or perhaps another appliance that may be more appropiate

Inflamation: Hard to tell for sure without seeing you but there may be some inflammation that needs more time to heal... If wearing it more does not help see your dentist for further evaluation..

TMJ pain: This is difficult to say without an examination and more information. The pain may be due to when and how often you wear the bite guard, what kind of guard, whether there is inflammation or pathology in the joint. Some guards encourage clenching and exacerbate the TMJ dysfunction. Call your dentist.

Hard to say: Could be a number of things. Ask dentist who made splint. See a TMJ expert. 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.