The truth is we change the occlusion every time we use a handpiece on a occlusal table or incisal edge, Fortunately the changes we make are within the adaptive range of the majority of our patients and go unnoticeable. There are many occasions where we set out to alter the occlusal scheme a patient presents with. We can accomplish this through a variety of means including appliances, equilibration, restorative dentistry, orthodontics and orthognathics. These alterations are done with the intent to “improve” the patient’s occlusion. First and foremost “improvement” looks like eliminating symptoms, but beyond that are the signs of occlusal disease. For me, the concept of improvement, brings up a quote from Dr. Bob Barkley. He told us that our job was “to help our patients get worse at the slowest possible rate”. This is true of all we do, and absolutely true with occlusion. I have no belief that by altering how their teeth touch I will alter what they do with their teeth. Yes it does seem to happen sometimes that patients parafunction less on an appliance or after an equilibration, but those results are not predictable and often transient as those activities ebb and flow over time. What I can do in the face of the patients parafunctional and functional activities is alter the tooth contacts in order to minimize the stress to the joints, muscles and teeth into the patients adaptive range.
Occlusal adjustments can only ever accomplish two things. One of the primary reasons we alter how the teeth touch is to change the amount of force the person can apply. We have very good science that supports that posterior tooth contact increases the activation of the elevator muscles, thereby increasing the amount of force or load they can apply. This happens in both intercuspal position and excursive movements. When a patient presents with signs or symptoms that stem from forces or load that is too great, one aim of therapy would be to reduce this load. If we look at some general numbers adding in tooth contacts in the bicuspid region doubles the force over anterior contact. If we add contacts all the way back to the second molars, the force can be as much as five to eight times more than when we have canine contact. The force or load is shared by the teeth and joints, and experienced by the musculature. The percentage of the load distributed between the dentition and the joints is also altered relative to where the teeth contact anterior or posterior, but generally said lowering the amount of force is beneficial therapeutically.
The second thing we do when we alter a patients occlusal scheme is we design which teeth touch, and the shape and size of those contacts. In this way we can work to distribute the load across multiple teeth and broad surfaces, or focus it on a few teeth. One of the primary concepts in adjusting edge to edge position is to create big, broad flat contacts to distribute the load and protect the teeth or porcelain. The concept of canine guidance is to eliminate posterior tooth contact in excursions, thereby minimizing the force. This force is placed all on a small number of teeth. I’m sure you can see in your mind;s eye a few patients for whom this would not be a desirable situation. Group function on the other hand distributes the force over a larger number of teeth (canines and bicuspids), but the addition of the posterior teeth increases the total amount of force. There is no perfect solution, just the one that is most appropriate for each individual patient.