When you're looking at designing centric stops for implants, whether it's a single implant crown or a full-arch fixed prostheses, it's very important first to understand the difference between implants and teeth.
One of the main problems we see when we are restoring an anterior tooth that's just recently chipped is that we always have to adjust occlusion. Whenever you see a chipped tooth you have to ask yourself why. Why is that chip there?
When delivering a single crown, probably the toughest tooth we can prep for is the second molar.
There are a couple things to be aware of when prepping second molars:
1. Limited Opening
One, usually, there's a limited opening in that area, so when you are prepping the tooth, you have to give the patient breaks because you're going to have to ask them to open quite a bit.
2. Wear and Tight Neutral Zone
The second thing, which is more of a concern, is the wear in that area and also the tight neutral zone.
When looking at implants versus teeth, it is very important to consider the differences between them. There are many differences.
One difference that's very important for us as Dawson Dentists to consider is that a tooth has a periodontal ligament, the PDL. An implant does not.
An implant is essentially an ankylosed unit.
Fremitus is the perceived vibration of a tooth when it comes into contact with another tooth.
This is very important for a number of reasons. It is something we should look at in our new patient examinations and is something that we have to check and make sure that is not present when we are finishing occlusal equilibration.
Muscle exams are a very important part of our new patient examination process. There are several muscles that we look at, and it's in the Dawson Diagnostic Wizard ®. And they're very important to know if they're sore, and what is it telling us.
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As Dawson-trained dentists, one of things that is most exciting and fun for us is going over specialty treatment. Taking our patients to records and going over the checklists, the photos, and the Wizard, and figuring out a long-term treatment plan for them.
The problem is, that we experience at our office, is getting our patients to records. Some of the terms that we use are confusing and we lose them in the process.
As Dr. Dawson told us, a word such as equilibration is a word we should never use. There are a lot of ways, both Dr. Dawson and the lead faculty communicate to patients in layman's terms to help simplify the process.
In our smile design process, we have learned from Dr. Dawson how to develop incisal embrasures. And also from Dr. Dawson and the American Academy of Cosmetic Dentistry, how to develop the apparent contact zone between teeth.
So between two centrals it should be 50%, a central and lateral, 40%, and a lateral and a canine, 30%.
There are times, though, where, depending on the restorative interfaces, say, for example, two implants, we cannot create an apparent contact zone that falls in those parameters. And if we want to keep the incisal embrasures developed, as Dr. Dawson's taught us, we need to have a long contact zone.
One of the things that can negatively affect the result and success of our cosmetic cases is the appearance of black triangles.
There were two landmark studies and papers that were released in '92 by Tarnow, and Garber and Salama in '98 that talked about where to set the contact points depending on the restorative interfaces relative to the bone to prevent black triangles from forming.
Say, for example:
- Tooth to tooth set at 5 millimeters or less
- Tooth to implant, four and a half millimeters or less
- Implant to implant, three and a half millimeters or less.
- And there are other combinations.
The key is from our end, we have to communicate to the lab and let them know where to set that contact point relative to the margin.
For example, if you're restoring teeth numbers eight and nine and you want to prevent a black triangle from forming between those teeth, you have to let your lab know where to set the contact relative to the margin.