The temporomandibular joint (TMJ) is in front of the ear and the joint movements can be felt if you place your finger at that level. To examine the movements of this joint, the rhythm of the closing and opening of the jaw must be noted. The jaw should open and close easy and the teeth come together and separate easily.
If there is jaw pain, that will be a break in the arc of motion on the painful side with obvious movement of the jaw to one side or the other. When the mouth is closed, the line drawn between the tip of the nose and midpoint of the chin will be in the same vertical line and the jaw is centered well. The teeth can also close symmetrically in the midline. When the patient has pain in the jaw, the line drawn from the tip of the nose will not be able to go through the midpoint of the chin since the jaw will not be centered well.
With problems of the temporomandibular joint, jaw movements may create a clicking sound, due to problems with that joint cartilage. Problems with the inner lining of the joint known as the synovium may also be the cause that causes the joint to click. In such situations with trauma to the joint cartilage, the joint may dislocate when the mouth is opened as wide as possible.
This joint is prone to trauma especially in auto accidents where the head is thrown backward and the mouth opens wide in a sudden and forceful motion. The joint may dislocate in these positions. The cartilage as well as the joint capsule can be torn. Joint overload may occur when the head is placed in traction, or when a person has poor dentition or when a person grinds his teeth during sleep.
Testing of range of motion of this joint involves examining the movements of the mouth and jaw. Normally, the mouth can be opened wide enough to insert three fingers between the top and bottom teeth. Horizontal movements should be free enough so that a person when sliding the lower jaw forward, the bottom teeth can be placed in front of the upper teeth. Limitations in range of motion can be due to pain from arthritis of the joint or from muscle spasm.
Muscles involved in opening the mouth are:
- External pterygoid muscle supplied by the mandibular portion of the fifth cranial nerve.
- Hyoid muscles.
Muscles involved in closing the mouth are:
Primarily masseter and temporalis muscles aided by the internal pterygoid muscle. All these muscles are supplied by the trigeminal nerve.
In all cases of TMJ problems, it is essential to examine the movements of neck and shoulders and spine. Patients with neck pain who keep the head forward and downward can cause abnormalities in the line of action of the muscles which open and close the mouth and eventually put wear and tear on the jaw joint.
Therefore, treatments directed only to the TMJ will not alleviate the jaw pain problems unless head and neck posture is also corrected. Examine the muscles of the jaw and the masseter muscle, is easiest to examine. You can feel this muscle just above the angle of the jaw as you clench your teeth.
If there are myofascial pain problems, tight and tender myofascial bands can be felt in the masseter muscle. There can be tenderness in the temporalis muscle also which can be felt at the side of the head above the ear. It is essential to treat the myofascial pain problems not only for the muscles responsible for jaw movements but the treatments must include muscles of the neck in order to alleviate jaw pain problems.