We're going to answer some questions regarding the webinar that I did the other night on anterior guidance, and we have some very good questions.
What about group function? Is it only for dentures?
The answer to this is that group function is routinely, very applicable to dentures, but not typically for natural teeth, with the exception of patients who do not have an anterior guidance. If they don't have an anterior guidance to disclude the balancing side in excursions, then we have to use the working side in group function to disclude the balancing side. As long as we have an anterior guidance though, we do not want group function. We want just lines in front, dots in back with the anterior guidance separating all the posterior teeth in all excursions.
How is an implant in a maxillary canine position influenced by the principles of anterior guidance?
The canine in an implant case is still going to be used to disclude teeth posterior to that, whether they're implants or natural teeth. The one thing you want to be very careful of when you're using a canine implant is that it wants to be as flat as you can make it in the lateral excursion. And if you can bring in natural teeth to help in lateral excursions, you would want to do that.
What about guidance in class III cases, edge-to-edge bite or cross-bite?
Very good question. We want an anterior guidance to disclude the posterior teeth in all excursions whenever the jaw has a horizontal pattern of function. In class III cases, the patients go chop, chop. So it's a vertical envelope of function, and they don't really protrude. So in that case, we don't even need an anterior guidance to disclude the teeth in protrusive because the jaw doesn't typically protrude.
For edge-to-edge bites, you want a lateral excursion contact on the edge-to-edge parts of the teeth, which you can do. But in protrusive, you will just accept the amount of contour contact that you have as the incisal edges meet from centric to the slightly forward position. They still will not have a tendency to protrude.
Class III patients just don't protrude their jaw in a horizontal pattern of function. If you can't get that anterior guidance because of a Class III bite, again, that would be a reason for using group function on the working side to disclude the balancing side because these patients do have a tendency to go a little bit laterally in their function.
What kind of wear would you expect from a perfected occlusion just from tooth-to-tooth contact during mastication? Granted, it should be a very small amount, but to what extent: micrometers or nanometers?
You're close to being right, because number one, we don't expect any concern for wear in a perfected occlusion.
A perfected occlusion just does not wear out, because you can't wear what you can't rub. And if you have a perfected anterior guidance, then it won't wear out. So you can just go forever with that type of an occlusion, and you will never run into a problem from wear unless the patient is chewing on some abrasive materials.
Nevertheless, you will have some nanometer pore of wear probably from abrasion on food. But it will not be noticeable or of any concern at all.
How do I determine where to put incisal edge if all the teeth are missing? The patient has splayed teeth, inclined forward, and we want to eliminate an 'ape-like' appearance.
The answer to that question would take almost a little, mini-seminar here. So I'm going to recommend that you go to my book, Functional Occlusion: From TMJ to Smile Design, and look at chapter 13, Vertical Dimension (pgs 127-128). In that chapter I describe a method for establishing the exact incisal edge position of upper and lower anterior teeth as part of the method for determining the vertical dimension. It's well illustrated.
I highly recommend you study these pages because this information is a very important thing to know, and you'll use over and over. That's the easiest way to answer that question in light of how long it would take to describe the process without using those illustrations.
Regarding any patient who has splayed teeth, a lot of times the splayed teeth are in a neutral zone position because the lower lip gets locked in behind the upper anterior teeth. And so when you bring those teeth back into alignment, where the incisal edge of the upper incisors contacts the inner vermillion border of the lower lip (in the F and B positions), you're actually changing that neutral zone to where it should be. So there again, you want to understand how the neutral zone affects the position of the anterior teeth and use the methods described in our discussion during the webinar for locating that incisal edge.
The same with vertical dimension of occlusion, if we miss the correct vertical dimension of occlusion, for example, by implants or total dentures, is it possible that the bone around will somehow react to change it?
The answer is no. That's why we try not to miss the VDO with implants. With natural teeth you can increase vertical dimension and it will re-adapt to where the muscle wants it to be. But implants don't respond that way because all those changes in vertical occur in the alveolar bone on natural teeth, but you don't get that change when there is an implant in that identical position.
So it's extremely important that you get the vertical dimension absolutely correct if you're going to be using any implants in the mouth. You might also refer back to that chapter I just told you about. Because if you are doing an implant case on a edentulous patient, you have to determine that VDO very carefully, and this is the way we would do it. So I'll refer you back to that same chapter I just suggested a minute ago (vertical dimension).
How to moderate anterior guidance development by children, if it does not look conveniently?
I don't quite understand the question. How do you moderate anterior guidance development by children? Let me try to understand the question.
The one thing that you want to be very observant of in children--number one is airway. A child who has an airway problem because of enlarged tonsils or adenoids is going to be a mouth-breather. And as a mouth-breather, the tongue is going to be postured forward, which takes it out of the vault and pushes the anterior teeth forward, and that's a way of having buck teeth. By having the tongue out of the vault, the buccinator band can squeeze the arches into a narrow vault, also.
So airway problems are a potent trigger for ugly malocclusions. So you want to be sure and correct an airway problem in a young child as soon as you can logically do it.
Another problem that you have in children is disc derangements in the joints. If a disk becomes deranged on a young child in the early growth stages, that condyle will probably not grow to the same height as it should. So you will have a deviation on closure and opening towards the side with the deviated disc. If both discs are displaced, then that's when you have a retrognathic mandible. It's almost 100% that a displaced disc in a growing child is going to produce a malocclusion.
The implants in front do not have perception, so the strength are 100% like on molars, are not they?
Again, I don't quite understand that question, but implants in front don't have this sensory perception that natural teeth would have. So you just have to be very sure that they're placed exactly where natural teeth should be placed.
That's why you must determine exactly where the anterior teeth should be and the anterior guidance, and all that, and incisal edge position, has to be pre-determined before you put your implants in so that your fixtures are going to be aligned where you can then have the restorations that go in the implant are where they should be.
What's so often missed in implant cases is that implant prostheses is a prosthodontic discipline, and you have to make the determination of exactly where the teeth should be before you design where the implants go.
Should bruxers, who have been restored in ceramic, wear a B splint because of continued activity derived through the central nervous system?
Well, I think it's overblown that bruxism is going to continue to wear teeth if the occlusion is perfected.
Even with a bruxer, a perfected occlusion is not going to create a lot of problems with the wear if the anterior guidance is proper because there's not going to be any tendency to push or rub against a correct anterior guidance. And if the anterior guidance is doing what it should do to disclude the posterior teeth and all excursions then you're not going to wear out your posterior teeth.
So the question is again is going to back to getting the occlusion perfected. That's always the answer for preventing any excessive wear problems in any mouth.
What treatment approach do you take with patients who have a natural open bite?
Very good question. Number one is, you have to determine what's the cause of the open bite. Because if the open bite is purely the result of breakdown of the condyles, then that's a progressive open bite, and you're going to have to figure out how to get the joints stable before you make any determinations on what you do with the occlusion.
But the anterior open bite that is the result of a tongue thrust biting problem can be a very stable relationship. How would you know? Well, if you have the patient close to maximal intercuspal position, and they cannot touch the anterior teeth in maximal closure, then you can make that patient's occlusion in centric relation retain the anterior open bite. This is because the tongue is probably going to stay in there to stabilize it. There are many patients who can have a stable dentition with an anterior open bite if the tongue substitutes for the missing contact which should normally have.
This raises a question about, "Yes, well then what about anterior guidance and disclusion of the posterior teeth?" Well, here again, anterior open bites, typically, are chop-choppers because they get no benefit from protrusion.
You have to look in the patient and see if they're protruding, and if they are, then you're going to see wear, on posterior teeth, and figure that out, accordingly. But there are many anterior open bite patients that can be very stable because of a substitute of the tongue taking the place of tooth contact.
How does the anterior guidance relate to the articular eminence that drives the condyle down? Does it matter?
It seems that it does not matter so long as you get the posterior teeth cleared out of the way to allow the joints to fully seat and that no posterior tooth can rub so that the elevator muscles shut off.
I was thinking before the webinar that you might still put excess pressure on the front teeth if the condyle was not against the eminence while translating down the eminence.
That's a very interesting question because there's several things here that you have to understand. Let me take that last comment first: the idea that the condyle can go down the eminence without contacting the eminence. That doesn't happen. Your condyle disc assembly is always loaded against the eminence. Always. Because muscle always pulls across the joints, and this is a law of joint physiology. So the condyles are going to slide up and down that eminence regardless.
And the question of whether the articular eminence has any effect at all on anterior guidance, it does not. And that's been very clearly proven. Niles Guichet did an excellent study showing there's no relationship between the anterior guidance and the condylar guidance. And this flies in the face of an old belief of the gnathologist that said the anterior guidance had to be an analog of condylar guidance. And then they changed it to, it had to be within five degrees of condylar guidance. That's all wrong. Doesn't matter.
You can have a flat anterior guidance and steep condylar guidance or a flatter condylar guidance and a steeper anterior guidance. They're totally unrelated. And the reason for that is because the condyles can rotate as the mandible slides forward. So it can follow a different path than the anterior guidance without any interference.
The part you got really correct in this discussion was that you don't want the posterior teeth rubbing. And so that is going to be the result of both the condylar guidance and the anterior guidance to separate those back teeth as the jaw moves from centric relation.
Well, this about covers all the questions that we got.
I hope you enjoyed the webinar, and I really want to urge you to do a little more studying on anterior guidance. And I'd really urge you to go to my book and study those chapters on anterior guidance because there's a lot of nuances there that can make a huge difference for you as you start working with patients. So good luck, and I hope you got a lot from the webinar and the answers to these questions.