What are causes of a less than ideal bite?

In most cases, when there is a true TMD problem, there exists what is referred to as a “molar fulcrum.” The following images and narratives will attempt to explain and demonstrate this condition.

In this image a correct position for the jaw joint and teeth is demonstrated. Here the teeth make simultaneous and equal contact at the exact moment that the jaw joint is in its physiologically functioning position. The black arrows show that the force being applied to the joint is directly across the disc. Also, in this stable position, the muscles are in “neutral” (not firing), and no damaging forces exist to either the disc, the bony components of the joint, or the teeth.

This is where most TMD patients find themselves; the teeth are in a position where they make simultaneous and equal contact, but the jaw joint is forced out of a physiologically stable position. This position of the jaw joint leads to increased night grinding, increased muscular tension and damage to some or all of the following: the joint disc, bony components of the joint, teeth or the bone supporting the teeth.

In the third image the jaw joint pivots into a correct joint position with the forces now directed correctly across the disc and bony components of the joint, but the upper and lower teeth do not occlude in a stable, healthy position. Note that the point of contact (green area) is at the last molar and therefore the term “molar fulcrum.”

Patients with joint problems do not notice that they have this discrepancy present. The reason for this is that the muscles that control the joint position shift the jaw just before the teeth make contact. This is known as an “avoidance pattern” – the muscles move the jaw so that the teeth won’t crash into each other. But the joints suffer as they are now incorrectly positioned.

Molar fulcrums are revealed through splint therapy (see page on splint therapy). During splint therapy, the muscles will relax and the “avoidance pattern” will diminish over time until the “true” occlusion (bite) is revealed.