Can a doctor in the hospital diagnosis tmj 100%?

Your question is vague and confusing to me. Are you talking about an ER doctor or a hospitalist who sees inpatients in the hospital? These would not be the people I would have diagnose me. I would see an oral surgeon or an ENT for diagnosis/treatment. If you are considering another specific doctor, please reask question...

If you mean in the ER, the staff will have indications that they can discuss with you. However if you suspect a joint problem, see a specialist Oral Surgeon, Oral Pathologist, ENT, Orthodontist, or Dento-facial Pain Specialist. The ER is not equipped to treat your joint pathology.

That would depend on the skill & experience of the doctor. TMJ Dysfunction is caused when muscles and ligaments that cause your jaw to move are not working smoothly. If you chew gum stop. Eat softer foods next 2-3 weeks. Apply moist heat to the joint area. Stress plays a big role in triggering TMJ problems. Find activities to help reduce your stress level. See your dentist for more detailed help.