You might want to pick up a couple of basics before beginning this short article if this is foreign territory for you. My earlier article, TMJ Pain: Whose Fault Is It? would be a reasonable place to start. Knowing even a simplified version of the anatomy will help you picture what occurs when the disc is gone.
When the articular disc of the TMJ is displaced long enough, it will eventually perforate or—more likely– break apart. When that occurs, the mandibular condyle will actually contact the inferior surface of the glenoid fossa. In simpler terms, the top of the lower jaw bone—the mandible—will actually touch the temporal bone. Put those two bones in contact long enough and they’ll both appear to be wearing away.
Does that condition also change the patient’s occlusion? Definitely!
When discussing this situation with a patient, I often simplify things by saying, “The top of your lower jaw bone actually rubs against the temple bone of the skull, and the two bones can wear flat. The bone is literally going away and it hurts.” Now, I admit that’s an over-simplification and if you want to review the osteoclastic activity of bone under pressure that will give you a more realistic picture (Google: “Osteoclast”). But if you want to think of it as two bones grating against each other—and that’s certainly what it sounds like, that’s okay.
Also, if you research the subject of degenerative arthritis of the TMJ on the internet, you’ll find that most sites say that the condition almost always affects both joints at the same time. In my experience, that is simply not true. I generally find that only one of the two TMJs has degenerative changes. The other joint may be normal, or it may have varying degrees of disc displacement—but I generally don’t see the condylar beaking and flattening on both condyles at the same time.
When degenerative osteoarthritis affects another joint such as a hip or knee, there is not much to be done aside from daily pain medications and then surgery: total joint replacement.
Your patient with degenerative arthritis of the TMJ, however, can actually be helped with a properly designed oral appliance.
My approach with the arthritic patient is to design an appliance that will center the condyle or condyles in the glenoid fossae and, perhaps even more importantly, create some space between condyle and temporal bone. This accomplishes four important things:
- Pain is reduced and sometimes eliminated.
- Comfortable, stable occlusion can be achieved
- With space between the condyle and temporal bone maintained, the body will actually produce new soft tissue in place of the cartilage disc. Will this be a healthy cartilage disc? NO. The patient will never have a cartilage disc again. The new tissue growth will be more like scar tissue. But it will suffice. It will prevent the two bones from grinding against each other.
- The destructive degeneration of bone stops—no more wear and tear on the bone.
When discussing this condition with a patient, I tell her that the joint is arthritic and always will be. But, I can stop the degeneration of bone. I don’t promise to reverse the destruction, and usually don’t even suggest that can happen. Reversal however, meaning the return of a nice rounded condyle where there was a worn off flattened one, is possible. It takes years for that to occur though, and I do not count on it.
Once an oral orthotic is placed and the condyle-fossa relationship looks reasonable on x-ray, what then? First of all, I see the patient regularly to be sure that the occlusion is well balanced, the discomfort is decreasing and range of motion is improving. At some point, the condyle-glenoid fossa space will be maintained even if the orthotic is removed. This generally requires several months at least. Nine months to a year is not unusual. When the disc space is holding, I then check occlusion with T-scan. Because there is now some separation of the two bones, occlusion is usually improved. But is it improved enough? Occasionally, the answer is yes, and the patient is able to gradually wean off the oral appliance and still maintain disc space and comfort. However, more often the answer is no. In that event there are two choices: restorative dentistry or long term appliance wear. Some of my patients are perfectly happy to simply keep wearing the oral appliance. Their pain is gone, they’re chewing well—the appliance is essentially an overlay partial denture—and they know the destructive pressure on the bones has stopped. The second choice is restorative dentistry, and most patients prefer that option. Sometimes three or four posterior crowns on one side is all that is required if the overall vertical dimension is acceptable and the arthritis has created excessive occlusal force on that side. More often, it means a full mouth restoration. I let the patient and her dentist know when I believe she is ready for this step. When is the patient ready?
- If the TMJs cannot comfortably accept firm loading, find out why.
- Even if the TMJs can accept loading, ensure that they are stable before completing occlusal therapy.
~ Dr. Peter Dawson, Functional Occlusion From TMJ to Smile Design, Chapter 25.
Yes, that’s the answer. I make sure the joint can accept loading and also ensure that the joint is stable based on joint imaging and stable T-scan results.