Ideal Occlusion of Posterior Teeth

The following is an excerpt from my e-book, The TMJ and Occlusal Adjustment, which is available for immediate download.  The book tells the story of the occasional patient who has a temporo-mandibular disorder (TMD) that we can clearly link to an occlusal problem.  This specific disease, also known as occlusal-muscle disorder, can be effectively treated in your office as long as you know the fundamentals.  I review the essential anatomy, function, and dysfunction of the TMJ and share my philosophy of occlusion over the course of 40 pages.

In this excerpt we examine the occlusal marks left by articulating paper on posterior teeth.  What the heck should those dots look like?

Posterior Harmony

There are two popular theories of posterior occlusion that I will discuss.

Here are a maxillary right first molar and second bicuspid:

teeth
Figure 11: Maxillary teeth without occlusal marks.

 

My first study of occlusion was a philosophy known as tricuspidization.  The theory is that the most stable system for teeth is one in which three surfaces around the cusp tips occlude with the opposing teeth.  The cusp tips themselves to not occlude at all.  This results in a lot of dots left by articulating paper.

tricuspidization
Figure 12: Typical marks for tricuspidization.

 

As you might imagine, this is not a simple occlusal philosophy.  There are dentists that will defend it to the death and have achieved great success with it for their patients.  However I believe it is very challenging to create and maintain this occlusal scheme.  This is especially true when we consider a popular alternative: cusp-fossa occlusion.

Cusp-fossa occlusion is the occlusal philosophy adopted by many leading dentists, including The Dawson Academy and The Pankey Institute.  It is successful, simple to understand and easy to equilibrate.

Instead of the marks left by articulating paper representing contacts around a cusp, these dots represent the cusp tips themselves.  As we know, the supporting cusps are the maxillary palatal cusps and the mandibular buccal cusps.  So in our example we’d expect to see a mark on each of the three cusp tips:

cusp marks
Figure 13: Marks on the maxillary palatal cusps.

 

Of course, there will also be marks left by the supporting cusps of the opposing teeth, in this case, the mandibular buccal cusps.  Supporting cusps occlude in the opposing teeth in one of three areas: the central fossa, the mesial marginal ridge, or the distal marginal ridge.

opposing marks
Figure 14: Marks left by the mandibular supporting cusps.

 

So when a patient bites down on articulating paper, we should only see marks on the supporting cusps and the marks left by the opposing teeth’s supporting cusps.  Combining both Figures 13 and 14, we see what cusp-fossa occlusion should look like:

cusp-fossa
Figure 15: Cusp-fossa occlusion, occlusal view.

 

cusp-fossae cross
Figure 16: Cusp-fossa occlusion, sagittal view

I think you’ll agree that cusp-fossa is much easier to visualize and equilibrate than tricuspidization.  Just to drive the point home, here’s a picture of the two philosophies superimposed:

comparison
Figure 17: Comparison of tricuspidization (red) and cusp-fossa (black).  Note that the red marks form a tripod around the black marks representing the cusp tips or marks left by opposing cusp tips.

This concludes our excerpt.  If you’re keen to learn more, check out The TMJ and Occlusal Adjustment on this site.

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10 Comments

  1. Alaa says:

    seems very helpful book, thank u Doc for sharing

  2. Cuspy says:

    Interesting post. It seems, however, that natural anatomy and function is being sacrificed for expedience and simplicity. Just because one doesn’t understand something complex, doesn’t mean you can simplify it to make it easier to understand, ignoring what is difficult to comprehend or counter intuitive.

    The natural human tooth anatomy seems to indicate that the fossa and cusp shouldn’t occlude, and instead the inclines should make contact, and this makes more sense when looking at mechanical engineering principles, efficient mastication, wear over time, and how the nervous system works, something dentists rarely examine.

    Cusp-fossa occlusal design seems naive and over simplified to me, like a hack, or a shortcut, used to make treatment planning easier, not a reflection of how occlusion naturally works in the mouth. Millions of years of evolution is unlikely to be so completely wrong as the cusp-fossa design implies.

    • Chris says:

      Interesting. Thanks for sharing your thoughts. My question is which alternative occlusal philosophy you would prefer. It sounds like you are in favor of tricuspidization. Tricuspidization is not found in nature (or very, very rarely), regardless of the mechanical engineering principles behind it. Cusp-fossa, on the other hand, can frequently be found in nature. It’s not always found it its most perfect form of anterior guidance/immediate disclusion of the posterior in lateral function/etc., but pretty darn close.
      Adjusting a patient into tricuspidization is arguably more invasive because it sacrifices more natural anatomy. There are more slopes and contours that need to be adjusted throughout the dentition in order to achieve three equal points of contact around each functional cusp tip. It’s really more of a hypothetical concept in my opinion. There are dentists who have had success using it with their patients, so I think it’s perfectly valid. But one could make the argument that it makes things more complicated for the sake of engineering principles.
      It all comes down to the philosophy with which dentists and patients are most comfortable. I prefer the one that is less invasive, simpler to achieve, and closer to what is found in nature. I wouldn’t say that cusp-fossa is a simplified version of tricuspidization; they are different concepts. And evolution does not favor one philosophy over the other. Minor malocclusion does not prevent species from propagating.

  3. thanks for sharing.Ideal Occlusion of Posterior Teeth | The Curious Dentist gave me much help.

  4. Cuspy says:

    “Tricuspidization is not found in nature”

    I think you’d get an argument from many dentists on this point. I think of it like a camera on a tripod. You have three legs, which is a very stable situation, with force and wear distributed across the thickest part of the enamel with a large margin of error if things aren’t anatomically perfect. Its self adjusting too as one leg wears the others come into occlusion so its inherently stable.

    Cusp-fossa is like one of those one legged camera tripods. Yes the camera is still off the ground, but it isn’t nearly as stable. Simpler, and easier to manufacture, but not as stable or strong. If you were to look at the ground, instead of three shallow depressions in the ground you have one deep depression. You then have to rely on a few different teeth to get stability, which increases complexity and now there is more wear due to the singular occlusal point which then leads to increased loss of vertical dimension.

    Fortunately, over time as wear continues, as the cusp/fossa interface wears away, your cusp-fossa occlusion will end up with a three legged tripod or something similar.

    So it seems like tricuspidization or tripodization is unavoidable over time, and therefore perfectly natural, inevitable in fact. So evolution “favors” it, because over time, its mechanically inevitable.

    How is tripodization in any way more invasive sacrificing anatomy? I would say the opposite is true. You mention that it is but don’t explain why. I agree it might be simpler for a dentist to achieve, but don’t see how its more invasive or sacrifices anatomy. Can you explain why you think that?

    • Chris says:

      If we want to be accurate about what is found in nature, it isn’t cusp-fossa or tripod contacts. The occlusal scheme found most often in nature is malocclusion. If you want proof of that, just ask any orthodontist. So the nature argument isn’t very compelling to me. But even gnathologists like Albert Solnit agree that it is not often found in nature (check out his excellent book, “Occlusal Correction: Principles and Practice”).
      Leaving the nature argument to the side, my argument that achieving tripod contacts could be more invasive is based on the complexity of the adjustments required. More slopes and contours must be adjusted in order to produce three stable contacts around a cusp tip rather than simply having the cusp tip in occlusion. Personally, I don’t state that tripodization is an invasive procedure; I am stating that it could be argued that it is more invasive than cusp-fossa due to the cumulative effect of many, many small adjustments.
      This subject is one of those old philosophical battles in dentistry. We can both find board-certified prosthodontists on both sides of the aisle who will present research and arguments that one philosophy is better than the other. I can quote Dawson: “…there is no scientific research that tripod contact is more stable than proper cusp-tip-to-fossa contact. Development of ‘slides’ is common, even among the most meticulous of operators” (Functional Occlusion: From TMJ to Smile Design, pg 227). And you can quote Solnit or another gnathologist and we can go back in forth. What’s important is what works in your hands with your patients. If you are able to achieve stability and harmony with tripod contacts for your patients, then please do so. But there are many dentists who choose cusp-fossa as laid out by Dawson, Pankey-Mann, Christensen, etc. The cusp tip will be perfectly stable and will not wear as long as appropriate lateral function has been achieved.

  5. Cuspy says:

    “If we want to be accurate about what is found in nature, it isn’t cusp-fossa or tripod contacts. The occlusal scheme found most often in nature is malocclusion. If you want proof of that, just ask any orthodontist. So the nature argument isn’t very compelling to me.”

    Interesting perspective. Perhaps calling what is “normal” a malocclusion is a misnomer then. I’ve seen pictures of the most horrendous malocclusion in some tribesmen that don’t practice dentistry, and they function just fine, blissfully unaware of any problem, other than a perceived aesthetic one, which is obviously completely subjective. Personally, some “misalignment” or asymmetry of teeth adds character to a face, and in some cultures, creating what in the US would be called a “malocclusion” is all the rage for cultural, aesthetic, sexual or other reasons. IE: The snaggle tooth trend in Japan.

    Clearly there are subtle subconscious clues that humans pick up based on the shape and positioning of teeth, and perfectly symmetrical teeth is unnatural, especially given that the human face and jaw is also asymmetrical as anyone who has done the mirror reflection trick can attest to. Could it be that dentists are trying to force their convenient occlusal model into biology like early mathematicians tried to force PI into a rational number? Eventually they gave up and just accepted the irrationality. It must have been demoralizing for them, but at least their circles were now round.

    “I can quote Dawson: “…there is no scientific research that tripod contact is more stable than proper cusp-tip-to-fossa contact.”

    This means only what it says. There is no scientific research. I don’t think it implies that tripod contact is less stable than cusp-tip-to-fossa contact.

    “And you can quote Solnit or another gnathologist and we can go back in forth.”

    Does this imply that one philosophy is correct and one isn’t, or both philosophies are right, or both are wrong? Or that its really a religious argument, and perhaps the underlying assumptions have been misinterpreted leading to many opposing sects, like we see in religion? Or that each patient is unique and so any generalization of occlusion is wrong by definition? Or is it far more complex than has been realized so we are muddling along without much of a clue? How is a prospective patient to know which is the best model for themselves before undergoing invasive treatment?

    • Chris says:

      I believe that both the philosophies of tripod contacts and cusp-fossa can be used by an experienced dentist to successfully treat a patient. Personally, I do not believe that one is superior to another from the patient perspective. Both can be used to restore function. However, my point is that cusp-fossa does offer dentists the advantage of simplicity. The notion that cusp-fossa is easier to practice does not mean it is inferior to tripod contacts.
      For some dentists, however, this is like discussing religion. They will passionately defend their occlusal beliefs and bash the opposing side. I’m not of that mind set. What I am passionate about is that these philosophies are only practiced when necessary. If a patient is symptom free and shows no signs of TMD or occlusal disease, then I won’t suggest any equilibrations no matter what their occlusion looks like. Unfortunately there are dentists who will suggest equilibrations just because something isn’t perfect… whatever that even means. As long as a dentist is practicing their occlusal philosophy responsibly, then I have no concerns.

  6. Pingback: Simple Occlusal Adjustments to Treat Muscle Pain | The Curious Dentist

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