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Maxillary Molars

Feb
2014
21

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Watch the video: http://www.learnerstv.com/video/Free-video-Lecture-4747-Dental.htm

In this presentation we will discuss the anatomy of the maxillary molars. Our objectives in this presentation will be to discuss the location and position of these teeth, to concern ourselves in relation to the occlusion, to study the morphology and the terminology on these teeth and to study identifying characteristics of the maxillary molars. We’ve got 3 maxillary molars which we will be concerned with. They are simply called first, second and third. I should say we have 3 in each quadrant: 3 on the right and 3 on the left. On the right there would be tooth number 1, 2 and 3 and on the left it would be 14, 15 and 16. Our first maxillary molar is the one that comes in about age 6, very frequently confused with deciduous, baby or primary teeth. Next one, second maxillary molar, comes in about age 12. Our third maxillary molar, frequently referred to as our wisdom tooth (read about wisdom teeth removal), varies in its eruption coming in anywhere from 17, 18 up to late twenties. It’s the one that has such a reputation as being a troublemaker and frequently, I shouldn’t say frequently, about 20 percent of the time it’s not found at. It seems to be disappearing in its presence. If we look at the cutaway scull on this we can get an idea of the root structure on it. Notice that we are seeing two buccal roots on each of these molars. And we’ll also notice that the angulation is a little bit forward on all of these teeth. They are coming a little bit forward on their angulation. We should start to take more specific notice in relation to the occlusion of these teeth and how they are actually occluding with mandibular. We may have mention that our bicuspids actually are what we call interdigitating.

We’ve got a cusp-fossa relationship but more specifically we can turn this cusp-embrasure relationship because the cusp of the bicuspids is actually coming up and touching on the marginal ridge areas in our premolar areas here. We’ll define embrasure more specifically for you but this is an area associated with the marginal ridges. We still have a significant amount of difference in the width of our arches here, our maxillary arch being much wider than our mandibular arch. And the difference in this width is measure term cold which is called overjet. Overjet is the distance the maxillary teeth overlap the mandibular teeth in a horizontal direction. It is also called horizontal overlap. And we can take a look at our gauge here. We can actually put on a gauge and measure this amount by using the back side of our boley gauge and measure the specific amount that we would have in overjet and measure right down to a tenth of a millimeter or so. We’ve noticed that with these maxillary molars as they are interdigitating we are getting the combination of cusp to embrasure or to our marginal ridge and we’re also getting cusps associated with the central portion of our teeth or the actual fossas. So we get a cusp embrasure and a cusp fossa relationship on these molars. We’ll break down a little further as we go. If we look at the other side here we’ll also notice one other relationship I think we should take note of and that is that we have a maxillary sinus [inaudible] and this is [inaudible] width about apex of our maxillary molars. If we were to take our skull part here a we’d note that these roots have a tendency to be directly in a relation to these [inaudible], these maxillary sinus. [inaudible] often can effect these teeth. Actually the lingual root of this maxillary first molar is penetrating into the floor of the sinus and sometimes the roots of second or third molars may also penetrate into the maxillary sinus. This can lead to confusing clinical symptoms. If we go to our individual teeth we’ll start to identify some [inaudible] marks here.

Actually we’re picking up a lot of new terminology with these teeth here now but the terminology is not really complex because it is associated with the mesial distal buccal and lingual. Those are our four basic surfaces so we probably should identify those first. If we look at the tooth in outlined form here, this is the easiest way to really identify the buccal and the lingual because our buccal surface has a height of contour that is closer to the cervical. This height of contour can also be called the buccal cervical ridge or the cervical ridge. It is a bulbous prominence down in here and frequently will be just called the cervical rage, meaning the height of contour. And then from this area up towards occlusal we have a tendency to flatten a bit through the middle third and actually into the occlusal third until we get up to our buccal cusp. On our lingual surface our height of contour is [inaudible] through the mid portion and our lingual surface is more evenly convexed. So this is the easiest way to identify our buccal and lingual. In identifying our mesial and distal I guess the best way would really be to look at your occlusal surface because you have one cusp which is prominently larger than the other. And this is the mesial lingual cusp. And this is always to the mesial surface. Actually we have 4 cusps on this tooth and they’re identified strictly by the surfaces. We got our mesial lingual being the largest in bulk, also being the largest in height or the farthest from the cervical. We have our mesial buccal, our distal buccal and our smallest cusp usually which is the distal lingual cusp. So we are basically talking about 4 cusp tooth when we are talking about our maxillary first molar. Our second and thirds have characteristics very similar to these and as a result we’ll spend much of our terminology identification on this and then just point out the differences in second and third molars. We have basically the same line angles at the junctions of the surfaces.

We’ve got basically the same point angles on this. If we look at the buccal surface of this tooth we can see our mesial and distal outline. Our most important characteristic in this view is the height of contour. Our height of contour is similar to our maxillary premolars. On the mesial it is usually found in the occlusal 1/3. On the distal the surface is usually rounding more and the height of contour is usually found in the middle 1/3. Our overall width on this tooth is about 1 millimeter wider from the mesial…no, it’s a 1 millimeter wider from the buccal lingual dimension than it is from the mesial distal. So the tooth is usually similar to the maxillary premolars, wider buccal lingually than it is from the mesial to the distal. But the tooth overall is about 2 millimeters wider both on the buccal lingual dimension as well as in the mesial distal dimension than our premolars were. We’ve got some other rather strong characteristics on this tooth that we should identify for you and start to put some terms in. Again terms are very similar to the surfaces and the cusps what have you but the most prominent features on this tooth is our central pit. One of the biggest problems in this tooth because this central pit is usually very deep and often times has a tendency to become carious. Now we have a fossa around this pit area. Sometimes these fossas will be called triangular fossas because of the…actually apexing into this single pit. And we’re getting  groove from the central groove and the other grooves that seem to apex right in this. We generally [inaudible] triangular terminology. We’re just calling it a central fossa or mesial fossa or distal fossa or whatever it is and leave the triangular out. It doesn’t seem to add a great deal to the term other than just carrying some additional jargon with it. We have a mesial pit which is usually not nearly as distinct or located quite as prominent that it would be towards the mesial aspect of the tooth. We have a distal pit which is usually fairly prominent in the distal portion of the tooth. We have a central groove that connects up to the mesial pit but it doesn’t connect to the distal pit very well because we have a rather strong ridge that crosses the tooth. Let me see if I can point out this ridge to you here.

This ridge runs from the mesial lingual cusp distally a bit and then crosses the tooth to our distal buccal cusp. And this ridge is termed the oblique ridge. It runs crossways of the tooth not straight crossways but goes to the distal and runs across the tooth. Remember on our mandibular first premolars we had a transverse ridge. That was characteristic of the first mandibular premolar only. This oblique ridge is characteristic of our maxillary molars and very prominently in our maxillary first. It’s sometimes also in existence in our seconds and occasionally in our third molars but very prominent in this first. This will be a very important characteristic particularly when we get into restorative dentistry and reconstructing these for crown and bridge and [inaudible] and the variety of other purposes so that’s one area I warn you we have to know and know very well, it’s this oblique ridge across through here. There are two very prominent grooves on this tooth which we should point out and identify for you. One comes out in the central pit and comes to the buccal and it’s simply called the buccal groove. And it actually crosses the marginal…or I should say cusp ridge and it divides the cusp ridge. We’ll go over these cusp ridges in a minute. And extends down on to the buccal surface about half the way down on to the buccal surface but it doesn’t cross this cervical ridge or height of contour. Actually it comes right down the center almost of our buccal surface here.  The other very prominent characteristic ridge, or groove I should say, is this distal buccal… distal lingual groove, excuse me. Which comes out of the distal pit and traverses at an oblique angle and comes to the lingual surface. And actually it does cross the height of contour of the tooth down on the center of the lingual surface. And in the outlined form you can see a little dipping that exists in this height of contour down here.  Fact is it not only crosses the height of contour but it frequently in the maxillary first will go down and groove right into this root surface. That’s a very strong groove, particularly in the maxillary first molar. We have the same marginal ridge basically on our molars. Got our mesial marginal ridge and our distal marginal ridge.

Partial Dentures P4

Feb
2014
14

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They’ve looked at that for the last 40 or 50 years. Here’s that case basically in the mouth. You look at the one side, you look at the other. They’ve got this one pictured…cause this is the other side of the mouth. And what they’re using here is the proximal [inaudible]. There’s the try-in and if you go ahead and get teeth processed [inaudible]. Another lateral that has a longer span. Same thing. You got a long span here. You can look at this and you can block across to the other side of the arch. The idea is when you’re looking at into a case where you might think about using [inaudible] Definitely what you want to do is talk to your faculty, take a look at the case and decide whether rotational path is the way… Now swinglock removable partial. Basically this is what the framework would look like. This fits around labial of the teeth  with these little eyebars that come out vertically.  These little eyebars will engage into labial surface of the lower teeth. I don’t use these all that much anymore. Pretty much now with high speed instrumentation you can reshape the contour of the teeth fairly easily [inaudible] restoration without crowding teeth you can also build up undercuts where you need them. The other thing you want to know is that these frameworks will cost at least $200-$250 more than your conventional framework. So from [inaudible] and those folks it’s not uncommon for the framework to cost alone between $650 and $800. If the framework cost alone, you haven’t added teeth on, you haven’t processed anything plastic on it, if your framework cost alone is pushing six to eight hundred dollars you want to make sure you are being remunerated enough for the partial that you are not losing money on it. Several years ago one of our grad students did for a nice patient Mr Traylor and so we got the whole thing done anatomically. It was a very complex framework that overlaid the occlusal surface and everything else. We did the case and we were charging Mr Traylor basically the graduate fee for the partial denture which is around $1250 and that framework cost us $1800.

That’s a great business plan, isn’t it? If you’re losing money on each one of these you’ll make it up on the volume. Here’s accentuation also or some of these as I say [inaudible] the number of teeth missing or number of defects you’re trying to fill up is very extensive, it may be that the extra grip with the swinglock may be worthwhile. Now this is basically just a set of duplicate cast that goes through the sequence of how long these frameworks would be made, the standard blocking out they are going to go ahead and duplicate it. Here’s our study model and we go ahead and say how we’re going to watch the framework up. Here’s the wax up of the framework. Frameworks are waxed up as there are these  stainless steel spindles that are incorporated into the wax up and the reason this stick up into the air as far as it does is just so that it can fit into a dental surveyor, like a surveying tool, but what’s going to happen is after casting all of this stuff that sticks out into the air will get cut off. So all this is for is extra things to use it in the tool that seats these down so that the bottom part of these spindles will be incorporated into framework but the top 80% of these things will be just cut off [inaudible] and made smooth finishing of the partial denture framework. Here’s another view of the framework. Here’s your labial plate, here’s your maxillary labial view, here’s your two spindles. One side is going to be the gate side. That’s going to be the hinge. The only difference on these things is which side is the gate and which side is the hinge. After way up stage if you look at the cast metal this vertical part right here is the bottom part of the spindle right here. This part of the spindle right here is what you see here. The top part of where the spindle was here has been cut off and polished so this has been cut off and polished it’s what stands up in the air. Now on one side when they do the wax up of this they carry the waxing all the way around that vertical spindle. On the other side there’s going to be the snap in gate.

The wax up on that side is only going to surround about little more than 180 degrees. It’s not going to surround all the way around that spindle. So one side is waxed up all the way around it and that becomes the gate side. On the other side the waxing over here wraps around part of this spindle but doesn’t go around the 180 degrees. Then when it’s cast there is just enough surface contamination on these they will allow these things to open up and swing. Here is your hinge side so you can see when the waxing was done here unlike on the hinge side on the other side this waxing didn’t warp all the way around this spindle. Again this spindle used to go up into the air or up in the surveyor but the top part of it was cut off. So the only difference is instead of being waxed all the way around the spindle, it was only waxed partly around the spindle [inaudible] The other things is because these are totally interchangeable which side do you want to wax all the way around and which side you want to wax partly around, you should make these things open either way. Just depends how they’re waxing up [inaudible] If you’re thinking of doing one of these you want to ask if the patient is right or left handed. Which side will be easier for him to get a hold of this gate and snap them open, if they had a preferred side.  Here’s the situation clinically in which you look at the teeth from the anterior. We go ahead and basically have our partial denture here. Here’s examples of them. Here’s a swinglock .Again, we don’t need to do these so much anymore because nowadays there’s a high speed instrumentation [inaudible] materials that can alter the contour of these teeth to make them more favorable fairly easily. So if you see these used at all they will tend to be used in maxillofacial situations for the most part. These are ugly. Doesn’t this bite into patient’s lip? And isn’t that the food trap? We find with most patients that these have been done on [inaudible] Isn’t that the food trap?

Yes. But because partial can be taken out and cleaned and that’s your hope that the patient will continue to clean these things. Surprisingly a lots of patients when they smile these eyebars are located fairly close to the pregingival margin, they are not esthetically unsightly. So typically… here’s a nice lady, there is her upper denture but you don’t see lower swinglock partial at all. If you’ve got the same thing but with modifications face, the modification faces can be fitted on the partial and the gates just spin around the modifications face. Again with the materials we have available to us today I can’t justify anymore spending many hundreds more dollars for a framework like that when I can recontour the teeth to get a conventional partial pretty much the way I want it. These situations might be a little more challenging when you’ve got all the teeth on the one side. Again this shows a situation where you’re trying to clasp those teeth a little more firmly. You got these teeth clasped pretty firmly and this is our replacement teeth. Again the thing that is not available during your practicing lifetime. But I’ve been thinking about rather than taking a real expensive framework would be in a situation like this…over in this area is considering putting one or two dental implants over there strategically located. And then you can have partial denture in this area here it’s just under the partial denture in this area you’d have couple of [inaudible] attachments that were just snapped on. Again when these frameworks were involved we did not have that as one other option. Here’s another one that clasps teeth in two different ways. Again these are very expensive frameworks. They worked out okay but like I said I want to show you the swinglock partials as much as anything. If you heard of them you sort of know what some indications might be. Mostly maxillofacial. And nowadays when we have dental implants available to us and the possibility of recontouring teeth much more easily either by [inaudible].

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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