The canted plane revisited: One thing you MUST check

Dr. Halligan

Dr. Halligan

The mysterious 25%; the Princess and the Pea

Mrs. Hightower (not her real name) came to me last month for a TMJ exam. According to her dentist—and according to Mrs. Hightower herself—she had no history of TMJ pain. She had never had jaw clicking or limited opening and never had a problem chewing.  And then her dentist did a single composite filling to replace an old amalgam on an upper left molar. At that point “all hell broke loose,” according to Mrs. Hightower. Her bite felt totally wrong. She had jaw muscle pain. She had pain when chewing.


So, I proceeded with a TMJ exam. One of my first steps was to observe the frontal occlusal plane. To do this I simply place a tongue depressor sideways, left to right, just behind the canines, and ask the person to close. Mrs. Hightower’s occlusal plane was obviously off. The tongue depressor slanted up on the right side. As most of you know, this means there is probably joint pathology.


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How strong is the probability? Seventy-five percent, or thereabouts. Why is that? Because a canted frontal occlusal plane is usually the result of unequal ramus length. And unequal ramus length is usually caused by a disruption in one of the two growth centers of the mandible (the epiphysis). The disruption is usually caused by partial or total disc displacement sometime before the growth spurt that occurs in mid-to-late teen years. In other words, the disc displacement happens first, then the unequal ramus length follows. Even if the patient is unaware of the problem for years or even decades. “Oh, I always had a clicking jaw;” the patient might say, “ever since I was a kid. But it didn’t hurt like this until now.” How many times have we heard that one?


Oh, and by the way, I use the word usually three times in the above paragraph. Some authors of peer reviewed research papers would confidently substitute the word always. I happen to think that Always is a very big word and I’m much less likely to stretch credibility quite that far. Sometimes there are other, less obvious causes.


Also, all of the research on this subject uses the word, “Obvious” when describing the canted frontal occlusal plane. What constitutes obvious isn’t always made clear in the literature, but it appears that the occlusal plane when viewed from the front must be at least 3 degrees off, and sometimes much more than that, to be called obvious. Therefore, we are not talking about subtle facial asymmetries that most would agree are quite common and fall within the norm.


If a canted frontal occlusal plane is the number one predictor of a TMJ problem, then obviously all dentists should do this simple 10 second screening step with a tongue depressor. And if the patient has a history of clicking or locking, if the patient has tenderness in the muscles of mastication or in the joint itself, a thorough TMJ evaluation is a must. Ignoring that and doing those 6 to 8 veeners you’d like to do in the presence of joint pathology is simply not a good idea.


But what if your patient has a canted frontal occlusal plane, and you find that there is no joint pathology at all?  What if you find that your patient is one of the lucky 25 percent? What now? Can you just proceed as you would with any other patient? Until recently, I would have said yes. If the temporomandibular  joints are normal on x-ray and a thorough exam rules out joint pathology, then there should be no cause for special concern.


But over the past year or so, I’ve come to another conclusion. This is not scientific. I base this instead on my experience and observations. My bank of experience though is growing rather substantial. So, here’s my opinion: a person with an obviously canted frontal occlusal plane is one of those unusual dental patients who is exceedingly sensitive to occlusal changes. The canted plane needs to be seen as a warning sign whether you are doing restorative dentistry or orthodontics.

I suspect that the young lady in the fairy tale The Princess and the Pea had a canted frontal occlusal plane.

Anybody who can feel a pea through 8 mattresses is also the person who can feel the slightest high spot on a filling. This is the person who can tell when a new restoration causes even a small change in her occlusion.


I think we’ve all had patients who, after we’ve placed even the most conservative restoration on an occlusal surface complain that it just never felt right. You check occlusion with articulating paper and it looks normal, at least on first glance. And yet clearly something is wrong. You may have decided that it must be a psychological problem. Here’s a suggestion, the next time that happens, reach into your box of tongue depressors. You will often (always?) find that this very sensitive patient has a canted frontal occlusal plane.


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Again, this is speculation. The following however is not speculation. If your patient has a canted frontal occlual plane, and is one of the 25% who does not have joint pathology, my experience says there is still something noteworthy going on. Perhaps it is as simple as laxity of the ligaments that should hold the disc in place. But I have seen this situation often enough to make me believe that even in the absence of true joint pathology, there is some underlying problem that has the potential to make life difficult for the restorative dentist or orthodontist.


When I discussed this subject with Dr. Michael Miroue, a local orthodontist, he had this input: “What transpires is the mandible is the primary driver of the occlusal plane cant. The maxilla secondarily adapts to the canted mandible and via sutural growth becomes canted also. The mandibular position thus becomes the template for the maxilla. If the cant is mild, ortho can treat it via TADs (mini screws or implants). If the cant is more severe, surgery is indicated.”


For a more detailed look at how orthodontics can correct a canted occlusal plane, please click here to see a 1MB PDF attachment.


What about the patient I mentioned at the beginning, Mrs. Hightower? T-scan showed that #15, the tooth with the new composite, was the first tooth to contact when the patient closed. It also had contact when she went into left lateral excursion. The composite actually included enough of the buccal cusps that it forced the mandible to shift to the right when the patient closed. The result was TMD symptoms with no joint pathology. And just to make life more interesting for the dentist, the occlusal problems were not especially obvious when I checked with articulating paper.

I could have reached for my QuietAir handpiece and corrected the occlusion myself, and sometimes I do. But I prefer not to touch another dentist’s work unless he or she requests I do so.

But I can print out the result of T-scan and send that to the treating dentist as a kind of road map or guide to the correction needed. And getting rid of high spots and areas of interference usually solves the problem.


The take-home message? Be very suspicious when you see that obvious frontal cant. First be sure you’re not dealing with overt joint pathology. For the person with a canted plane and normal joint health, beware that the person in your chair may be the Princess who could feel the pea. When you place a restoration for this person, check and double check for any prematurities. Lateral interferences can be difficult to spot. Of course I have the advantage of T-scan. But I also use a technique I learned more than 40 years ago at USC. I check centric occlusion and lateral excursions with two different colors of articulating paper. I use a standard blue or black to mark centric occlusion, then red Accufilm for all other excursions. If you dry the teeth and then look very carefully you’ll probably spot an interference that you didn’t know was there. Then get rid of it. Then check again.


I’m sure future research will find a reason why the Princess is so sensitive. It’s not her (or his) fault and most if the time it isn’t psychological either. Future research may also provide treatment options not yet thought of. But in the meantime, take your time and be extremely careful with these folks. And maybe remember one of Omer Reed’s famous maxims: sometimes the best dentistry is no dentistry.



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