Getting The “Sharpness” Right on Your Restorations

Have you ever had a patient say they have a hard time chewing, yet their teeth are clearly making contact? Maybe they even said their teeth are not "sharp" enough, as I had a new patient tell me some years ago.

So why are they having problems chewing? Typically this issue is due to the occlusal anatomy being too flat, meaning that the cuspal inclines are too shallow or flat. If these inclines are too flat, the patient may have a hard time chewing efficiently. However, if they are too steep, they will bump these inclines, which won't work either – as they will likely end up with sore teeth and/or broken restorations. The complicating factor here is that there is no one magic angle to set these inclines that will work for all your patients. Figuring out the right angle for each of your patients is what I would like to discuss in this article.

The first thing to remember is that our patients' teeth do not actually touch when they are chewing; rather they chew by a series of near-misses. This is the whole reason we must get the steepness of the occlusal table right. The next question is, why do some people need a steep occlusal table while others need a flat occlusal surface? The reason behind this comes from movement of the condyle against the eminence in the fossa, referred to as the posterior determinate, which creates posterior guidance. Patients with a flat eminence will need a flatter occlusal table, while patients with a steeper eminence will, you guessed it, need a steeper occlusal table.

So the question now is, how do we determine the slope of our patients' eminence and take that into account when evaluating our patients' occlusion and having our restorations fabricated?

While it may seem like the steps needed to account for this would be complicated and involved, the good news is it is not. In fact, it is really quick, simple and easy. All we have to do is take a protrusive bite or photograph of our patient biting in protrusive with their lips retracted and use them to set the condylar inclination on our articulator which mimics the angle of our patients' eminence.

When using the bite to set the condylar inclination, you simply seat the bite registration between your mounted models and adjust the condylar setting until the base of the condylar housing is just in contact with the mandibular element of the articulator. It is important to note that you need to make sure the contacts only lightly touch. If you want to use the photograph to set your articulator, simply move the mounted models into the protrusive position you photographed and then adjust the condylar settings until the models mimic the teeth in your photograph.

If you are asking yourself, "How can I be sure I get the angle exactly right using these methods?" rest assured, you just have to be fairly close and this will provide the level of accuracy you need.

For even more details on this check out this article by Dr. Gary DeWood.

John R. Carson, DDS, PC, Spear Visiting Faculty and Contributing Author [ www.johncarsondds.com]


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