Partial Dentures P3

Feb
2014
07

posted by on Gum Disease Prevention

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Length of the span. This just sort of looks at that one situation  saying if we’re doing it front to back, if we’re doing like the upper fixture that is class 4 partial that things are going to seat here first and then rock down distally. The shorter the span is the more you got to block out. And further away you are so that radius, the radius of arch that you’re going on, as that gets longer you got less block out because the things are becoming more [inaudible] that’s upper or lower. If the rotational axis is fairly straight across the arch side to side, when looked at from the front it’s also fairly [inaudible]. What happens when this partial denture is going to rock in place is going to rock pretty straight down in place. Cause you see here depict is the situation in which posterior plane of occlusion was uneven from side to side. Let’s say for whatever reason this tooth sits farther in the air than this tooth. So instead of going like this, this plane goes downhill like that. Can you see that if the plane was tilted like this [inaudible] coming down. People follow that? So the height up and down of the posterior teeth [inaudible]. Cause if they are the same height things are made level level. They are at the same height. You see the posterior path you rock it down and your arch is seated very straight down. If the two teeth at the back that you’re using as your primary rest are significantly not at leveling height so that height runs this way. Can you see that when it arcs forward it’s going to arc that way and that can cause you problems on how you block out or how well it seats on the anterior teeth. It’s basically the position of your rotational axis both in terms of is it straight across and also is it leveled. Cause again imagine that you are on two different teeth here and it was pronouncedly angular that way.  So that would effect how the rotation happens. If it just sucked nobody would do it. The thing with this is labs really have to [inaudible] and the labs have to be up to speed to work really well.

Pretty much. The only thing in the question was are these so complex to put in that people have the hard time doing it? Not really. They go in as easy or easier than the conventional partial. Conventional class 3 in this situation right here you’ve got four sets of clasps all [inaudible] your teeth. So as far as how tight these things are going in you can see what’s seating it and taking it out. [inaudible] against the retentive features of four different clasps [inaudible] If it’s a rotational path then literally people toss them in after about 2 days they get really used to sort of feeling how it goes in. Cause it’s not that it’s a lot harder to put in. It just doesn’t go absolutely straight down. They got to consciously let the back part seat in first. But what really does wind up is that they’re really finicky to design and for the lab to do them so that they work well their finicky but if you find the lab that work that way they really work out well. In many of these cases [inaudible] mesially and lingually tilted molar, it’s really easy to do these kind of partials instead of trying to find some way to figure out how you’re going to get your framework to fit around those tilted molars. They are a little more challenging to design and your lab has to be on their game to make these things come out well but when they do they aren’t any harder at all for the patient to physically place or take out. Actually they are  little bit easier. And the shape of the arch. The more V shaped the arch is you block out different areas. If the arch is pretty much square and straight front to back you don’t have to block out that much on the lingual of the teeth. If the arch is real V shaped [inaudible] you got little more block out to do on the distal lingual. Again, all of this stuff is in your book. If you’re looking at your undercut then what you want to see is that this class 4 partial that you were going to do is just like the one that’s on the cover of the Krol book. [inaudible] I’ve got some undercut on the mesial proximal on these cuspids. The other thing you want to look at when the surveyor is at level is to see how much undercut do I have at that back tooth. Will anybody care to tell me if I have a problem with that undercut right there what’s my problem? I’ve got some undercut but what’s wrong with the nature of the problem? You can see that my height of contour is absolutely at my occlusal buccal corner and I’d like the height of contour a little bit further down on the buccal of the tooth. [inaudible] The occlusal buccal corner of this tooth a little bit so we still had undercut down here at the cervical but undercut was softer and it was more gentle curved. Cause again if your height of contour is absolutely at that occlusal buccal corner there is no gentle curve for the clasp to flex over and seat. And then you go ahead and tilt the cast so that you are looking for your secondary path of insertion you tilt the cats posteriorly till you see the surveyor shows that [inaudible]. If I say that’s my secondary path of insertion and that’s primary path of insertion there’s whole new amount of undercut I have available to use is the difference between the two surveys. In this particular case we used as illustration, I can pretty much work out the survey that will let me use entire proximal of that as my undercut on my rotational path. Its’ the difference between the undercut between the two paths of insertion. Go ahead and put a set of marks on your cast of the level survey and you put a secondary set of marks on the tilted posterior survey. Two sets of surveying marks on these casts. One [inaudible] level level. And the other has tilting [inaudible] and pretty much eliminated the undercut on which ever proximal surface you are using for your rotational path. The rest seat preparations on these mesially tilted molars or lingually tilted molars. [inaudible]  the reason we do elongated rest is because we are not having any reciprocal or [inaudible] or clasp on the buccal. When the framework engages this elongated rest over time the tooth will tilt and rotate. If I had just one tiny circle, this tiny dot for a mesial rest, over time the posterior tooth would [inaudible] around that rest but if it’s a long rest, if it’s a channel, the tooth can’t rotate or tilt at all. So in those situations where molars are [inaudible] So again if you look at these things if the teeth are tilted labially if you were to imagine taking a [inaudible] that would come straight down the lingual of that tooth, to have your framework clear on the surface of the tooth, it has a hard time resting against soft tissue. SO then your elongated rest will just use the occlusal and mesial proximal surface and you don’t care if there is no undercut on the buccal and you don’t care if the tooth is tilted labially. Here’s one of these sets of dividers that you can set up to different separations and if you can make two arms parallel to one another then you can look and set one arm [inaudible] and when you rotated down you’d see a block out. In these cases the area inside the dotted line or the area between the dotted line and the tooth, would be the areas that would need to be blocked out for the framework to be able to seat when it is rotating in. We’re going to show just some different examples of patients.  Here’s basically the back to front.

So we go ahead at either one of these you just seat the framework from the back to the front, there’s your framework with set teeth on [inaudible] this seats first and rotates down the place with the clasp. We go ahead and get the teeth set up on it. So right away you see it’s all processed. We just got this elongated strap rest on the posterior molar. We got a clasp up front of these seats. [inaudible] forward, clasp goes down. So as long as this is seated the back arch can’t pull out. Front to back. You go ahead and look at these many [inaudible] We go ahead and get things set up. Here’s a framework. So this framework engages the mesial proximal of those teeth next to dentulous area. And then it locks posteriorly and seats over the posterior teeth. Here’s your replacement teeth and what you’ve got is no clasp. So you’ve got a situation where you are not showing any clasp. Here’s AP category one meaning that [inaudible] completely here and then just rock the clasp down in place. Here’s the same thing with longer spans. Then go ahead and front part of the framework seat is done. You see the distal down. No clasps. [inaudible] We got a clasp back here where it doesn’t show. Lateral. It’s the same thing that they show you in that book. Here’s one [inaudible] Basically you’re missing some teeth here so we are planning on laterally rotating from here across to here and so we will be clasping on these teeth. Here’s our edentulous span. We get our framework made. Again the framework engages the proximal [inaudible] so what do you? You first survey is what everything lateral and what you’re looking at there [inaudible] You are looking for where is your undercut on this tooth [inaudible].

How much undercut? [inaudible] More is better so that if we got much in excess of ten thousands we may not need more than ten thousand, fifteen at the most. But let’s say in the ten. If you can see some daylight when everything is levelled we see a nice undercut here and we can see daylight on either of these proximals. And when we do or secondary tilt, we tilt the laterally and I’m tilting it laterally to see if daylight disappeared and these things become perfectly parallel the that’s our secondary path of insertion. So the total amount of undercut available to you on those proximal surfaces is the difference between levelled and tilted.

I do because they’ve done many studies both for fixed partial dentures and for removable partial dentures. Depending on how tooth is tilted. [inaudible] and the tooth is tilted this much or it’s tilted more severely this much if you go ahead and [inaudible] if you are touching at all at the marginal ridge, even if there’s one undercut that you can use [inaudible] as long as it engages at that marginal ridge coming around the corner a little bit this tooth cannot fit mesially because it’s got a block there. And when they’ve done photo elastic studies on it vertical pressure right down here on these mesially tilted teeth [inaudible] fixed partial denture or removable partial that touches right there photo elastic studies tell you that the forces are directed along the long axis of the tooth. Cause it can’t lean over any more mesially if something’s in the way even if it’s just the first millimeter and a half to two millimeters up by the marginal ridge. So if it can’t fall mesially no matter how much you push down on, the forces are directed along the long axis of the tooth.

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