Partial Dentures


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Now the thing about rotational pass concepts is basically it’s the cover of your book .So those of you who have got Krol manual I mean the picture that’s right on the cover of your Krol manual shows both an upper rotational path and a lower rotational path. So that’s the cover straight off your book so we’re going to go over it. If this were a standard class 3 partial dentures, the lower picture. If you had a molar on each side and then you went up to a first bicuspid with this longer span. If it were a conventional class 3 partial it is a non-rotational path partial, the path of insertion for the partial would be straight up and down. Now sometimes some of you that had worked with [inaudible] partial dentures where you got these teeth at the back end for the lower partial, you may or may not be aware many times you got these situations in the mandibular arch this molar posterior tooth is very off and tilted mesially and lingually. How many people had one of those? [inaudible] You got this lone standing molar in the back and it’s sort of leaning mesially a bit and it’s leaning lingually a bit. So if you’re thinking of trying to [inaudible] to give you a nice straight path of insertion it’s reasonably difficult because many times where the tooth is leaning lingually if you’re trying to find a path of insertion that will let your partial denture come down past that lingual cusp of the tooth, when it gets down to interior edge of the framework it nowhere near the tissue and you say “Gee, I might have a hard time [inaudible] lingual of that tooth.” And similarly for a mesial tilt. In the upper case as it’s shown right on the cover of your book you can see many times if you have got clasp [inaudible] partial denture upper clasp [inaudible] replacing the anterior teeth, one of the downsides of in the upper partial or upper partial replacing the anterior teeth,  are these guys right here, that is the clasp.

Now I would argue that the way they designed the clasp on this particular partial looks reasonably good. [inaudible] The clasp is an [inaudible] clasp so it stays up fine and it contacts the tooth very near pregingival margin so that’s not an extremely ugly clasp as clasps go. But many times you may be able to find a situation in which you can do a rotational path partial and eliminate the clasp on the anterior aspect of the partial completely. In this case it would be front to back rotation. Then the lower example that you see for the class 3 it’s the posterior seats first and then once these rest seats are in place you just [inaudible] the anterior down in and [inaudible] posterior rest seats first, [inaudible] the anterior down in and when it’s totally seated, the proximal plate back down the molar literally takes advantage of the fact that there’s a undercut on these molars. It uses it. So you start to seat the partial in the back first, rock it down so now that it’s fully seated they back can’t come up because you have engaged the proximal undercut. Then the situation here is a similar situation only from front to back and we’ll talk more about that later. So what are general considerations? If you got a rotational path all of your seats do not necessarily seat simultaneously. It’s not a straight path of placement. It’s a curved path of placement. Many times you can eliminate unesthetic clasps.  The clasps are replaced by rigid retainers is what we need. In the case that we’ve talked about before in the posterior aspect no need for a clasp here because the rigid retainer being the proximal plate of this partial denture framework, once the partial denture rocks down in place there is a good occlusal rest on this and then the proximal plate rocks in to the undercut. So as long as the partial denture can’t move mesially, this can’t come up. It’s rocked in. As long as this stays down this is rocked in. So clasp in this case would be replaced by a rigid retainer [inaudible] proximal plate and the occlusal rest. So we don’t plan on the retainers flexing. If it’s a clasp you plan on the clasp flexing over the height of contour and coming to rest at the desired [inaudible] undercut. If it’s a rotational path that part of the rotational path framework it seats first and then you rock it to place. That’s what really [inaudible] rigid retainer just by going in and rocking to place [inaudible]. So the rigid retainers do engage undercuts and with many of these there is little tolerance for error because if these are off just a bit there can be problems. How many people so far have delivered as definitive partial, I mean the partial that’s got a metal framework and the [inaudible] teeth on half of it? Little less than half. So for those that have or for the people that are about to deliver some partials what [inaudible] is you try the partial denture framework in to make sure it fits okay if you take a bite registry.

So you say “Gee doctor this framework fit pretty good, we got the occlusion adjusted and we took a bite.” Now you come back and you go to deliver the partial with the teeth processed on. And very many times when you go to deliver the partial now that the teeth are processed on you come and get me “Gee, my partial denture won’t seat. I can’t get it into place.” What’s the only thing that’s changed? It’s that we got teeth and plastic on it. So in many of those situations what happens is where the plastic has being processed meaning where there is a tooth set out here and there is pink plastics processed in here, many times as you are trying to seat partial the pink plastic plate interferes with the undercut you are trying to engage. As with many of these there’s not a lot of tolerance for error. Why do we always have you people [inaudible] or your partially [inaudible] on the surveyor table?  So that it’s leveled front to back and leveled side to side. We talked about this over and over. Sometimes in the preclinic even, and in the books they were talking about at the time I was in school, I was always sort of left with the impression when I took partial denture undergrad that if you put a cast, just took a model out of the patients mouth, took an alginate [inaudible]. If I fiddled with this thing enough on the surveyor [inaudible] I can find some orientation of this cast that will satisfy all the requirements necessary to make a nice partial denture framework. I was just always too dumb to find it. But supposedly if I [inaudible] enough…well what really what should have been happening is just orient the cast  so that the occlusal plane is leveled front to back and leveled side to side, draw a design that would be my most ideal framework design that I would like to draw, forget the contours and the teeth. Just draw a nice design.

Now go back and look at the teeth. Now if you got your design drawn you say “Which areas in the teeth are going to work with the design I’ve drawn? And which contours on the teeth, typically axial contours, are fighting me, are not working with the design I’ve drawn?” Now the reason we want to orient the cast leveled front to back and leveled side to side is if I want an undercut where I’m looking for the desirable undercut for the clasp, again, where do we want those clasps to engage? We want the clasps to help hold the partial denture in place, to resist the tendency for the partial to be pulled out of the mouth when people eat sticky foods. So any time you’re eating sticky foods once your teeth come together when you start to open your mandible, open your lower jaw, during the first millimeter to two millimeters of opening of your lower jaw can everybody see that the direction that your lower jaw is going to be in is pretty much perpendicular to the occlusal plane. I know the jaw opens on the arch. I know that. But can you see just the first 2 millimeters of movement? That first bit is pretty perpendicular to the plane of occlusion. And once you’ve opened 5 or 6 millimeters, the partial is already off the teeth be it a jujube or a gummy bear for the time your front teeth are 5 millimeters apart, the partial is already completely unseated. So it’s just during the first couple of millimeters of opening is when you want that resistance to displacement. So since during just the first millimeter or two of opening if there’s [inaudible] the direction of the vector is pretty nearly perpendicular so I got to find out what the desirable and undesirable undercuts are for my proposed partial perpendicular to the plane of occlusion. See if I can do a lot of gymnastics, if I can really orient the surveyor table all over the place to try to find some orientation where I can [inaudible] the point is that‘s not the direction that people are going to chew.  Okay?

When they open their jaw the vector is not going to go over this way somehow, it’s going to come straight up here.  So if I orient my cast in some odd orientation to find an undercut but when I bring my cast back level level front to back and side to the side, if that undercut now goes away that’s a false undercut. Because a false undercut is one that you can orient the cast somehow to find it, the question is does this still exist when the occlusal plane is leveled front to back and side to side? Cause that’s the direction that the removal [inaudible] is going to fall on the partial. People call that [inaudible]. as easy as can be. Put it on the darn framework, level front to back and level side to side and then start analyzing the contours of your proposed [inaudible] teeth. [inaudible] do they tilt lingually? Do they tilt lingually so far that it would be difficult to seat the framework? Cause there is difficulty if you’ve passed the tooth and still haven’t touched the gum. Many times if they lean lingually so that the lingual of the tooth is in the way, what do you suppose is the situation out at the buccal of the same tooth in terms of undercut for your [inaudible]? It ain’t there. There are things leaning lingually so  just looking at the orientation of the teeth when we got things oriented when we…when basically our cast is leveled front to back and leveled side to side. Then again these pictures. I’m not going to go over these things [inaudible] because these are all straight out of your book. I just stand them. So the thing here we’ve talked about if you got linear path of insertion everything goes up and down at the same time. If there is a mesial undercut here we brock it out parallel. If there’s an undercut here we brock it out parallel.

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