“PERMISSIVE INTERCUSPATION” What is That All About!?!By Michael McDevitt on June 29, 2015 | comments
Both Dawson and Okeson have clearly taught us that when the mandible is moving in the direction of the maxilla in the centric relation closure arc and tooth contact is made there are two options.
- One is that the teeth come into full contact in maximum intercuspation and both condyles remain fully seated in a stable relationship to their respective fossae.
- The other option is that the initial contact with a tooth or a limited number of teeth results in the requirement for dislocation of one or both condyles from their stable centric relation to their fossa.
Though not stated in either of the texts in my references, it seems that the issue of teeth being mobile rather than very firm is not addressed. I assume each author is describing these anatomical findings relative to a dentition of tight teeth. But what if the initial tooth contacted in the centric relation closure arc was mobile rather than firm? What effect would that have on our clinical diagnostic findings and, if it were true, how would we discover that experience?
The other option is that the initial contact with a tooth or a limited number of teeth results in the requirement for dislocation of one or both condyles from their stable centric relation to their fossa. Though not stated in either of the texts in my references, it seems that the issue of teeth being mobile rather that very firm is not addressed. I assume each author is describing these anatomical findings relative to a dentition of tight teeth. But what if the initial tooth contacted in the centric relation closure arc was mobile rather than firm? What effect would that have on our clinical diagnostic findings and, if it were true, how would we discover that experience?
As a periodontist, I suspect I find tooth mobility in my patient’s dentitions at a greater frequency than most, if not all, restorative dentists. As you all know, periodontal inflammation and bone loss can readily increase the chance of any affected tooth becoming mobile at a clinically observable level. The distribution of this damage seems to favor posterior teeth, especially molars for a variety of reasons. If the tooth that represents the initial contact in the centric relation arc has lost enough support and/or the inflammatory condition of its supporting tissue is sufficient to permit movement of this tooth, is it possible, even likely, that closure can continue without dislocation of a condyle?
I initially observed this phenomenon when non-surgical therapies resulted in reduction or resolution of periodontal inflammation and tightening of previously mobile posterior teeth. The firmer or firm condition of those teeth allowed me to clinically identify those teeth as the initially contacting teeth and an observable slide from centric was seen that had not been present at the patient’s initial occlusal assessment. To simplify the description of this patient experience I began to describe it as “permissive intercuspation.” The movement of mobile teeth allows closure to or closer to maximum intercuspation than could occur if that tooth were tight.
I have had the advantage of taking multiple courses at Dawson and Pankey and while teaching at Pankey for over 20 years to verify my ability to be able to direct patients into repeatable centric relation, so a complete occlusion examination is a routine component of my care for patients. Likewise I have learned the value and necessity of diagnostic casts accurately mounted on a quality articulator in (or extremely close to) a patient’s actual centric relation. Fortunately stone models demonstrate very little mobility of their stone teeth so a reliable reference for initial contact in centric relation is always available.
The clinical image (Fig. 1) is of a patient who closed in their centric relation arc, then squeezed firmly and attempted excursions in what some call a “power wiggle.” The numerous surfaces marked seem to indicate the presence of multiple potential centric contacts and multiple excursive interferences. The image of that patient’s articulated casts (Fig. 2) showing the initial contact in centric relation and the mimicking the clinical excursions by releasing the articulator’s mechanical condyles shows few contacts.
The best interpretation I can offer is the second molar or molars were the initial contacts and they moved to permit maximum intercuspation. The marks on the cuspids suggest they were the next in contact when excursions occurred, but they were mobile enough to allow the extensive marking in the patient’s power wiggle. For those of us who are firmly convinced that occlusal trauma can amplify and even direct bone damage for a patient experiencing the inflammatory state of periodontitis, this seems a critically valuable diagnostic reference.
Ironically perhaps, it appears that periodontists could enhance their diagnostic regimen and accuracy if we all gained the necessary training and skill is accurately mounting diagnostic casts on articulators and learned to find the apparent initial contact in the centric relation closure arc of our patients with periodontal disease. Check this out and see what you find, you might be surprised, as I was.
1. Dawson PE: Functional occlusion from TMJ to smile design, St. Louis, 2007, Mosby.
2. Okeson JP: Management of temporomandibular joint disorders and occlusion, ed 4, St Louis, 1998, Mosby.
Michael J. McDevitt, DDS, is a Contributing Writer for Spear Education www.periogeorgia.com