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.

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