Repairing Complete & Partial Dentures P4
2014
Now, the secondary things that happens is if you look at this, here’s some cross-section. Look at it from the top. Tuberosity, palatine fold here midline. So, what happens basically is when you talk about the depth and the shape of the posterior palatal seal, right at the midline and right at the laminar notch, the carpet padding under the mucosa is fairly thin. If you take a ball burnisher and you go push on these areas, if you push here and here and here, it’s not all that squishy. The carpet padding’s fairly thin so when you’re making the depth of your post dam, the butterfly shape, we come not to but through the laminar notch and we give a little blip up here, come back, a little blip, come back around here.
Why are the blips going around here? Two reasons. These are the areas where we’re most likely to get the air leak because, again, of the shrinkage of the denture. When it went up, it pulls away. Those are also the areas where the carpet padding’s the thickets. The accessory salivary glands, the submucosal fatty tissue, those kinds of things are thicker in here and in here. So, sometimes, if the soft palate moves up in the air, it tends to drag up the tissue just a little bit. Can you see that the thicker the tissue is, the squishier the tissue is?
Here’s my hard palate. There’s my soft palate moving up and down, and this fist is the back end of my denture. So, my denture back end of it ends right at my knuckles. So, here’s your hard palate. Here’s your soft palate. Here’s your denture and soft palate. It moves down. When the soft palate moves up, can you see that the thicker the tissue is here, it might pull that tissue up a little bit more and let air leak over the top?
So, the thicker the subcutaneous tissue is in those areas, the more compressibility exists on this very back edge of the hard palate. You’re still on the hard palate, but you’re at the very back end of it, and there’s some thickness to the end, especially some thickness to the subcutaneous connective tissue.So, the thicker it is, if this flexes up a little bit, it’s going to drag that tissue up a little and let air leak over the top. That’s why we make these things a little bit deeper and a little bit broader in these areas.
Now, the other thing that people want to remember is, again, for even some of my colleagues that will do this with fluid, some of my colleagues, if I look at the shape of the maxillary denture, in the old days I’ve seen them do it. So, when they get done with the fluid wax under this thing, they say, “What in the hell is that?” They’ll say, “I’ll get a better seal. I’ll get a better seal.” Basically, if we want this denture to displace this tissue just a little bit, can you see the only thing keeping the denture in place is interfacial surface tension and spit?
There is no wing nut that this thing’s screwed up in there with. So, can you see that there’s a limit to how much soft tissue you can displace? So, if the air’s going to leak, where is it going to leak? It’s only going to leak to this very, very back edge. So, these post dams don’t need to be that wide in an anterior and posterior direction because you displace that much tissue up because all you’ve got holding the denture in is spit and interfacial surface tension.
So, by trying to cover up a much broader area with your post dam, you get the net effect of what I call this then acts as cross country shoes or snow skis. So, you don’t compress the tissue at all because you can’t compress the tissue that much. So, what happens basically is it touches up here by the incisive papilla. It touches back here and is in contact with a lot of these areas. You wind up with not that great a retention. So, making post dams extremely wide in the A-P direction is not necessarily a great idea, and making them really deep isn’t a real great idea because I’ll take my bur and I’ll just cut this sucker here really deep. We’ve got a groove in here. It’s just kicking butt.
What do you supposed you’re going to see when the patient comes back for their first? Maybe when you deliver it, it’s got good retention. What do you suppose you’ll see when they come back for their first post-insertion adjustment? Their tissue is redder than this marker is right there. It’s bleeding. It’s ulcerated. It just hurts like hell, and for you just to make them comfortable, you can’t just go zzz, zzz. No, no. You’ve got to hog and grind and hog and grind until finally they can tolerate having it back in because the tissue’s all red as heck and it’s all swollen. It hurts like a SOB.
You finally grind it back enough so that they can tolerate having it in. Now over the next two days, what happens to the tissue? It shrinks back down and settles down. Now, how retentive do you suppose your denture is? Not at all. So, areas that you don’t want to screw around with too much are the post dam areas because it’ll cost soreness post-insertion. Then, when you try to adjust it, you’re going to overshoot the mark and the denture’s going to lose retention. Then, you’re like a dog chasing his tail or a snowball rolling down the hill trying to get this thing back to where it should have been in the first place.
So, don’t make your post dams way too wide A-P. Don’t make them grossly too deep. As wide as they make the post dams are half the diameter of the medium skinny acrylic bur. You know your tall one looks like a tall, skinny Christmas tree. Half the diameter of the tip of that bur is deep enough for the post dam. Maybe slightly more than half a diameter in these fleshy areas, but, for sure, not more than half the diameter of the midline and where it goes through the [42:25] areas.
So, if I stop anybody in the clinic in the next six months and say, “How come we do a post dam? What’s the function of a post dam for your palatal seal?” “To make the denture’s stay in.” Yeah, from what? So, what are the two things we’re compensating for? One is processing shrinkage of the denture. Remember when I talked about that when it shrinks to the middle, and if I’ve got a steep palatable vault, it may pull away from that in this area? Yeah? Processing shrinkage, don’t be a bit surprised if this shows up in the exam. Don’t be a bit surprised.
So, posterior palatal seal will help compensate for processing shrinkage, what else will it help compensate for? Movement of the posterior aspect of the tissue in the hard palate because of the flexion of soft palate. So, when the uvula and the soft palate flex up, it can compress or cause that tissue at the very back edge of the denture to move up just a little bit away from the processed surface of the denture and let air leak over the back.
So, it’s basically for soft tissue compression or movement where the back of the hard palate goes up and down or compresses a little bit because of the movement of the soft palate and dimensional change or processing shrinkage of the denture after processing. That’s why we do posterior palatal seals.
So, here’s one. If we poured a case out, we just grabbing that posterior palatal seal in. I’ll typically cut it in. Wow, I’ve really got you folks now. Talk about sleepy time. So, we’ll go ahead and cut it in with a bur and smooth it out with a number 7 wax spatula. It works really nicely. Here’s a different phases of we poured our index so we cut the back off. Here’s two different ones actually. They look the same.
Again, the color doesn’t match perfectly if I put the pink triad on, but it’s in area where it’s not seen. It makes a really, really nice contact with the tissue. It does a very nice job.
Class, prepare. We’re going to go over very quickly. What we’ve got here is we’ll ahead and take an impression. We’ll pour the impression out in medium or heavy body PVS. We get things poured up. We say, “Gee. In this area, we’re going to add a tooth, and we’re going to take this eyebar clasp and move the eyebar clasp from here up to here.”
So, we go on the inside of the partial and take a high speed round diamond, and we cut the eyebar clasp out of the way so it’s now free. I’m going to cut little tiny divots on the side of it to set things in. It’s going to go back on my model so what do I do? We add acrylic and we put the tooth in so the acrylic and tooth gets put in. The eyebar gets moved forward to the lateral incisor.
Can I always do that? No. What if they have some other clasp? They have these free made clasps that are either for the left side or the right side. So, I can go ahead, get a model, take one of those clasps and get some ortho pliers. Bend a little loop on these things. When I get the little loop bent on them, they can go ahead and be embedded in self-curing acrylic. So, we embed them in the self-curing acrylic, and we can add these little clasps on here. These are available at the desk.
So, here’s one where we’ve added clasps on the side. Here’s one where we’ve added a tooth and moved an eyebar. Again, this is our old friend the PVS model injected right into an alginate impression. Why? Because I don’t have to block out any undercuts, and I can take the partial off and on this model without breaking any teeth on the model.
A crown to fit your pre-existing partial, a tough thing to do. If we have a really good impression of the crown, we prep the crown, and we can go ahead, sometimes and just make a duplicate. This happens to be a DC pattern resin. Take an impression, a single impression of the tooth margin and wax our impressions on, cast the thing up. So, here’s our recast crown fitting the pre-existing partial. It only works if the crown is all gold, and it’s in good shape before we ever start.
Many times to do a tooth, a crown to fit a pre-existing partial, what the lab wants you to do is reseat the partial in the mouth is prepared and tissue packed, and when you take the impression of the tooth, go ahead and take an impression. Pick the partial in the tooth, and have everything up and send that to the lab. Disadvantage is what? The patient’s got to be without their partial during the entire time the crown is fabricated.