Removable Partial Dentures
2014
see the video: http://www.learnerstv.com/video/Free-video-Lecture-4817-Dental.htm
Welcome to the University of Michigan Dentistry Podcast Series, promoting oral care worldwide.
So, what we want to look at today are design considerations for the various types of partial dentures. So, we run through the class I, class II, class III, and class IV partials. When we look at class I partials, generally, whether we look at premolar abutments or there may be canine abutments in either arch. Sometimes, we might have a premolar, a canine, or a lateral incisor, very rarely to have lateral incisor as an abutment.
So, if you look at different type so fulcrum lines again in your text, page 96 talks about different fulcrum lines. Rather than bore you and go over all that, what you want to look at is there’s going to be a fulcrum line axis for tissue-directed forces meaning when people bite down on hard foods, and if we have a free ended distal extension partial, we expect the distal extended portion of the partial to be compressed towards the tissue a little bit. Again, the tissue is more compressible than the teeth are in intrudable. So, if you think of biting down on a tooth and a tooth socket has got a periodontal ligament suspending, it literally intrudes in its socket a little bit.
So, if you’ve got a class I partial that has a bilateral distention and you’ve got bicuspid abutment, when you bite down on the partial, the bicuspid abutments intrude a little, and the soft tissue that supports the distal extension bases of the partial also squashes down. So, the compressibility of the tissue in several factors many magnitudes more than the intrudability of the teeth into their socket which results in a distal tipping a little bit of the partial. So, that’s your fulcrum line or your primary access on tissue word directed forces.
There’s also another fulcrum line. That’s the retentive fulcrum line meaning if you eat sticky foods, when you open your mouth and something’s sticking to the distal extension aspect of the partial trying to pull the partial denture away from the tissues. There’s also a fulcrum line for that, and that fulcrum line is typically going to pass through the retentive tips of the clasps.
So, if you have a clasp on either side of the arch and the object or the partial part of that partial denture that’s going to resist movement that would try to lift it out of the mouth are the clasps. Where is the retentive aspect of the clasp? It’s at the terminal third where they’re the most retentive and they go into the undercut. So, a line passing through the terminal third of the clasp tips would be the fulcrum line on a force going away from the tissue.
So, you’ve got a couple of different fulcrum lines, not just the one going toward the tissue but another fulcrum line for forces trying to take the partial away from the tissue. This is gone over extremely thoroughly on the chart on page 96.
Indirect retention. What happens with indirect retention is when you have a partial denture framework, the finished partial denture that’s trying to be taken away from the tissue, you’ve got your primary fulcrum line for retention, and the indirect retainer helps brace the base. Now, the biggest purpose for a third point of reference or indirect retention on distal extension partials comes in to play when we are doing realigns of the partials.
So, if you have a patient in for a periodic recall, how many people have had a patient in for just a checkup? You’re doing a prophy on them, and you’re going to go ahead and check them up. They’ve got either a combination case that’s either a denture versus a partial denture, or they’ve got a partial denture in one or both arches. So, how many people have had patients like that in just to do a follow-up? Three of you? A third of you?
The point is what do you look at when we say evaluate their partial? So, how do you evaluate partial? How is it doing? Okay, good. Did you evaluate a partial? How did you do that? “I asked Mrs. McGillicuty if it was doing okay”. What did she say? “She said it was fine.” Did you do anything else? So, one of the things that one would do in a distal extension partial is how would you determine whether or not a distal extension partial might benefit from a realign.
One of the things is PIP. A simpler way is if we know when the framework was constructed. Let’s say, for the sake of argument, that the lower partial denture was done so that the teeth we had for this lower partial that you’re imagining is we had first bicuspid through first bicuspid left in the patient. So, we made a lower partial denture framework. We made a lingual plate on it so we had an occlusal rasp and a clasp on the first bicuspids, and we had a lingual plate that went around the lingual aspect of the front teeth.
So, if I would say, “How do you know if the partial denture needs a realign or not?” Just try to make it go teeter-totter across the primary fulcrum line. Can you see if you take one finger, gloved-hand, of course, and hold the lingual plate across the teeth and put another finger on the first molar area of the partial? See if you can teeter-totter it front to back. Everybody with me now?
If you can see the lingual plate area that’s on the lingual area of the anterior teeth noticeably lift up off the teeth so that when you push down on the molar area, you can see that the back end of the partial tilts down. Then, that part of the partial framework that fit in the lingual aspect of the lower lingual teeth lifts up in the air and comes up away from the teeth.
You see the only thing that can cause that is if the gum tissue on the underside of the distal extension base has remodeled, as resorbed and reshaped itself. So, the gums under the distal extension base don’t lift up under the partial as good as they did when it was first made. So, when a brand new partial is put it and you look at it and you look at it to see if it will teeter-totter front to back if it’s a bilateral distal extension, you don’t expect to see a lot of this tipping back and forth on a new partial.
Over time, a year, two, three, four, what’s going to happen is the soft tissue’s going to remodel a little bit so when you go to do that same pushing back and forth, the tissue isn’t supporting the back end of the partial. It goes down, and your indirect retainer is your point of reference because if that lifts up off the teeth, it’s telling you that you’ve got teeter-tottering. Question?
The question was, “If you have a class III partial that’s hypothetically supported at all four corners,” so there’s no distal extension and at least according to the record, as much as we can believe the record, the provider at the time said things fit well and everything was okay at the time it was delivered. You are now the poor sucker who’s doing the recall a year later when you’re cleaning their teeth or doing whatever and you try this class III partial denture in, and it seems like it rocks quite a bit. It just doesn’t fit on the teeth very well.
We’ll go over class IIIs in a little bit, but if basically your partial denture is tooth-supported all the way around, would any change in the soft tissue, if the gums reshaped a little bit, would that, in theory, have any effect on the fit of a class III partial? That has nothing to do with it because it’s tooth-supported all the way around.
Now, typically, if a patient is being compliant and wearing their partial on a regular basis, would you expect that the partial denture framework fitting on the teeth will help stabilize the teeth on that position when the partial’s delivered if, in fact, things fit well, which they said it did in the record? Is that a reasonable assumption? So, if a patient fits like socks on a rooster, there’s nothing really bad. When you eliminate the impossible, everything left, however improbable, is probably the cause.
So, the patient was either non-compliant and didn’t wear it, which allowed the teeth to shift. I don’t know how many of you have undergone orthodontics, and for those of you that did orthodontics, did you wear retainers for some period of time? If you got lazy because you’re just a human being and you went several days or a couple of weeks without wearing your retainer, when you put your retainer back in, it felt like it didn’t fit so good. It fit pretty bad, in fact. Just after a day or two, things seemed to settle in, and the teeth readjusted to fit your retainer. Same thing happens with a partial denture.
So, if I have a situation like you have, I either assume one of two things, the patient was non-compliant and didn’t wear their partial for some period of time. It’s been the dresser drawer for some period of time, and they put it in for when they came in to see you. Now, it’s your fault because it doesn’t fit, or they dropped it or the dog got a hold of it because patients lie.
It’s like You’re stopped by the cops or you see the gun machine come up in your rearview mirror, right? So, what’s the first words out of his mouth? “Do you know fast you were going, ma’am?” “No, officer. I didn’t have any idea. I’m the Virgin Mary here. What happened?” You know, people are not the best as saying, “I was doing 20 over. I’m in a hurry. It’s my fault. Put the cuffs on me. It’s my fault.” Probably, if you said that, you could blow the officer over with a feather, and they’d let you off with a warning just because they’d be so blown away that somebody was just so upright honest with them.
So, to answer your question, my greatest suspicion in that circumstance is they were either non-compliant and the teeth shifted or they dropped it and they got banned. Go ahead.
Did the tooth in question that had this sort of miniscule resin on this tooth, did it have any buckle or lingual dressing on the tooth? So, the point is that you can have somewhat of a minuscule resin, but if there’s some sort of a retentive arm, bracing arm, or a clasp arm on the buckle lingual part of the tooth, it’s unlikely that it’s going to shift that much if it’s being worn on a moderately regular basis. Again, if the partial’s being worn on a regular basis. If they’re not wearing it, absolutely.
It’s probably going to keep tilting it, but if the partial’s in place, it runs slant into the approximate on the partial. Even if the occlusal were to break off, you might get a little tissue irritation around that tooth because in that area the partial would be freely sliding up and down around the tooth, but because of the proximal plate on the partial, the tooth would have a heck of a time tilting more easily if the partial was being worn.
So, again, when I see those things, especially with an all-tooth supported partial and with students because they push you all over the place. I can’t tell you how many years it’s been. That’s one advantage in dentistry of getting gray hair. I can’t tell you how many times over the years I come into the cubicle, and I tell the patient verbatim exactly what you just told them six minutes before I got there, and they’re going, “Yes, doctor. Okay, doctor. Yeah. Uh huh. Okay, doctor.” Then, they leave, and then you come up to me after clinic. You go, “I want to send that person to the moon because I said exactly the same thing you did, and they said, “Are you sure? I don’t agree with you.”