Today we know that there is no fixed center of rotation for the human mandible. With a facebow transfer, however, we still align our casts as so there was such a center. But that is not all.

In order to hold on to this useless cast orientation while avoiding the frustration of having to locate a non-existing hinge axis, we resort to average facebows and align our casts with reference to the ears.

Since the ears are not necessarily positioned symmetrically to the skull we abandon relevant parameters like the midline, horizontal, vertical and sagittal planes in the process. Why do that?

In order to orient dental casts to a hinge axis of which we know that it does not exist!

Is that worth dealing with articulator artifacts resulting in the need for chairside corrections, or having to deal with poor esthetics when delivering crowns, bridges or prostheses? Especially if we have to buy into those mistakes with complicated instruments and procedures?

Hinge Axis?

We adapt patients to a technology relying on doctrines of the past, even in regard to the plane of reference we commonly use. And we expend lots of money and labor doing it!

Why not adapt technology to the patient? Why not return our focus to important parameters? Why not do better with less effort?

Define the direction of mandibular movements by the ears?

Stooping to technology?

When mounting casts in the articulator using an average facebow it is automatically assumed that the ears provide a reliable reference since the presumed hinge axis is aligned to the articulator parallel to a connecting line between the external ear canals. When studying dried skulls it quickly becomes obvious, however, that few are formed symmetrically. If the ears are not positioned symmetrically, the mid-perpenticular to a connecting line between them does not correspond to the midsagittal and all directions as represented in the articulator become unreliable. How smart is it to leave critical dimensions as these to chance?

 
Solution.html
Home.html