The topic of stable occlusion is confusing enough without having a common understanding of the terminology involved. CR, ACP, CO, MIP, FSJP, TMD, OMD … it's enough to make your head spin, or maybe just your mandible. Please, someone get me a splint to relieve this tension!
Often when discussing an optimal condylar position for restoration, we hear clinicians say that they restore in CR. However, if you choose this position and look in the Glossary of Prosthodontic Terms, you'll have to decide which variation of the seven definitions you will decide to use. I believe the simplest and most understandable definition was the one synthesized from the seven by Peter Dawson: the relationship of the mandible to the maxilla when properly aligned condyle disc assemblies are fully seated in the most superior position against the eminentiae irrespective of vertical dimension or tooth position.
The only caveat to this definition, which also exists in other definitions, is this: What constitutes a properly aligned condyle disc assembly? In its pure form this would suggest that the diskal tissues are intact in their entirety and not deformed or displaced. But what about the significant number of disks that are damaged at the lateral aspect but have the medial portion intact? Does that disqualify them from the definition of CR? More importantly is this clinically relevant? Of course the answer here is, “It depends.” If the condyle disc simply is not intact, yet it can be fully seated and functional in a reproducible state, then the definition of adapted centric posture (ACP) might apply.
These definitions are more than just semantics; properly applied, they can help us understand the biology of the joint and help with risk assesment. In addition to the pure instability of the joint as a result of degenerative change, the volumetric loss that is the result of any degeneration influences our restorative capability and predictability. In one instance, just consider the potential increase in balancing interferences when the joint has a displaced, non-reducing disc at the lateral aspect and is moving laterally in translation.
Perhaps most confusing is the liberal use of the term centric occlusion. By definition, (again from the Glossary of Prosthodontic Terms) centric occlusion is “the occlusion of opposing teeth when the mandible is in centric relation.” This makes both anatomic and logical sense in that the condyle is centered in the fossa. I think it would be safe to say in our current clinical context that this definition of CO can also be applied in “adapted centric posture.” What is confusing is how often the term CO is used to describe what maximum intercuspal position (MIP) actually is.
In my personal clinical and teaching experience, it is rare to find an uncorrected dentition that is naturally in a harmonious balance in CO, that is to say MIP=CO. And, most importantly, in a search of the literature, it has been extremely difficult to identify the frequency of centric occlusion equaling MIP in the general population because of the misuse of the term.
Again, in an effort to be more accurate in our diagnosis as well as our treatment, we should use the proper terminology. In general, think of it this way: If you fully seat the condyle and the disc is in place, then the first point or points of contact in the path in the arc of closure of the mandible is centric occlusion.
We often confuse the treatment we prescribe as a substitute for a clear diagnosis, and in this age of increasingly individualized care it becomes even more important to differentially diagnose the conditions our patients present to us. Only then can we offer the choices of care that may be appropriate to their individual circumstances and objectives. First we all have to be speaking the same language.
(Click this link to read more dentistry articles by Dr. James 'Jim' Otten.)
James “Jim” Otten, D.D.S., Spear Visiting Faculty and Contributing Author