I know even the mention of the words centric relation probably has some readers bristling, as this is a much argued over topic. With that said the research by Lundeen and Gibbs at the University of Florida shows that we do seat our condyles into the fossa during the chewing stroke. This seated condylar position is often used as a reference position to treat patients whether as part of reorganizing their occlusion to alleviate TMD symptoms or for restorative or orthodontic treatments. The next question is do people seat their condyles other than during normal function as part of the chewing stroke. I believe the answer is yes. One of the pieces of evidence is the number of patients that I have with wear facets that correspond exactly to their first point of contact with their condyles seated. These same patients do not mark this area with articulating paper in intercuspal position or when following their excursives.
I ask the question “Is Wear Normal?” at almost every lecture I do on occlusion. Usually the response is a small number of mumbled replies. A good follow up question is ” How many eighty-five year old patients have you seen with mammelons?” I hope your thinking not many, if any at all. So yes tooth wear of some amount is normal. A combination of attrition, erosion, and abrasion we all lose enamel over a lifetime. The more important question is when is the wear age appropriate and when is it advancing at a pathologic rate? We don’t have the data to know how many millimeters of enamel lose is appropriate at every decade of life. In order to help with this answer in my office I play a mental game. With the picture of the patients current wear in mind and a knowledge of their age I imagine if the wear continues at the same rate at what age will their teeth be in jeopardy or need restorative dentistry to be saved?
Patients who have worn teeth can be some of the most disconcerting. Often we are unsure of when to talk to patients about wear and uncertain about how we treat it and how predictable the results are. I believe that some wear is normal. I base this on the fact that I have very few if any patients who are in their seventies or eighties and still have mammelons on their incisors. Wear is a concern when the amount of tooth structure being lost is out pacing the patient’s age.
I had a new patient come in for an emergency appointment with a fractured lower incisor. This is probably the best example I have seen yet of someone shearing off tooth structure down the lingual of a lower anterior. The patient was of course confused at how it happened. He did wonder about biting his nails, and sheepishly admitted to doing that, with good reason as he can’t play his guitar with nails. He wondered about possibly biting down on a fork many years ago, but really was reaching for some explanation.
I have heard different reasons for this type of fracture over the years. My intuition tells me it is a combination of different things, one being the patient’s occlusion. If I search my memory I would feel comfortable claiming I have never seen this type of fracture without wear on the incisors. So one piece of the puzzle may be damage to the tooth from wear.