TMJ is usually caused by the anterior rotation of the Atlas on the side of TMJ pain. The Transverse process of the Atlas is rather long and when it gets stuck rotated to one side or the other it will interfer with the normal movement of the mandible causing the TMJ joint to get inflamed. Ouch!!!
Quite easy to fix with a good upper cervical adjustment.
Parasites cause clenching of the teeth by the ammonia they secrete constantly stimulating the adrenals. It's like being on speed all the time. Tightens you up to include clenching the teeth.