The jaw joint is a turn-glide joint. A joint disc separates the joint into an upper and a lower compartment. The turning motions are performed by the upper compartment, whereas the gliding motions are performed by the lower compartment.
Previously, it was thought that the head of the jaw joint head needed to be positioned at the highest point of the joint socket. Today, it is clear that there is no ideal position for the joint head in the joint socket. The lower jaw only finds the correct tooth position through the interlocking of teeth. Therefore, if the mouth is kept open for an extended period of time, the brain—using special receptors—takes some time to retrieve the ideal lower jaw position.
We usually experience this upon waking in the morning if we have slept with our mouth open. This causes us to feel that our teeth are not really fitting together. A familiar bite sensation comes about after a while, when the periodontal receptors of the tooth suspension apparatus have readjusted the lower jaw muscles. Therefore, the lower jaw position is controlled by the interlocking of teeth.
However, the situation becomes different in patients with missing teeth. As already mentioned, in the past, the lower joint position was determined according to the position of the joint head on X-rays. It was thought that the ideal position of the joint head was at the highest point in the upper back region of the joint socket.
Many patients were forced into this position with new tooth prostheses, crowns, and/or bridges, with the result that many patients, who used to be pain free, began to experience considerable discomfort. This occurs because X-rays clearly show only hard tissues. However, in the upper back region of the jaw joint, there is a tissue-based nerve and vessel cushion that cannot be seen on X-rays.
Through the new, denture-enforced, lower jaw position, this tissue-based cushion is compressed, resulting in pain. Nowadays, toothless patients are rehabilitated in such a way that the jaw joint head rests in front of the socket. It is important that the patient feels comfortable with their new teeth.
Moreover, the bite of patients having teeth and not feeling any discomfort should not be changed at all.