Maxillary Molars P2

Mar
2014
01

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Distal marginal ridge is frequently just a little bit closer to the cervical. We have sometimes a groove that will come up to this mesial marginal ridge and occasionally will cross it just a slight amount and this again would a mesial marginal groove. Kraus text book talks about this groove. We haven’t found very many teeth in which this shows prominently enough to really point out. It’s not a really strong groove. Our real strong one is our central pit in our central groove that comes up to the mesial. Now we can look at these cusps and we find that we have ridges coming from the cusps, not only our triangular ridge that comes down into the central sulcus area. Again central sulcus would be a valley depression between our cusps and our central sulcus area pretty much includes our occlusal table. Remember our occlusal table is the portion in which our food divides and goes to the outside of the tooth or to the inside of the tooth into the central portion of it. So our triangular ridges will come down into our sulcus, central sulcus, area here. Now with our distal buccal cusp here our triangular ridge is what almost connects up to our ridge, triangular ridge from this mesial lingual cusp. We got several ridges, triangular ridges, coming down into the central area of the teeth. We also have ridges coming from these cusps which are cusp ridges but you have to be a little bit more specific in the terminology of these cusp bridges. Fact is we have two, for instance, two mesial buccal cusp ridges.

We got a mesial buccal cusp ridge on the mesial buccal cusp. And we got a, I should say, buccal cusp ridge…we got a cusp…mesial buccal would be…mesial buccal cusp ridge on the mesial cusp and a mesial buccal cusp ridge on this distal buccal cusp. So we may have to identify these further and say mesial buccal cusp ridge of the mesial buccal cusp or the mesial buccal cusp ridge of the distal buccal cusp. Let’s look at the root structure on these teeth. Actually as a group they are probably the most easily identifiable teeth in the mouth in so much as they have three distinct roots and they are the only teeth, maxillary molars, that have three distinct roots. And the root structure is quite characteristic between first, second and third molars but it doesn’t outweigh the prominence or characteristics of the occlusal anatomy.

The occlusal and crown anatomy is much more reliable than the root anatomy. Root anatomy varies. But on these 3 roots we’ve got specific terms for all 3 roots as we did for our multiple rooted premolars and even our multiple rooted mandibular cuspids. In the molars the roots are termed simply by the location. Now if we look at the occlusal to get our orientation mesially and distally here I would hope, we would find that one root comes out right under this lingual groove. And this is right in the center of the lingual surface and this is called a lingual root. Very same term and same type of location as we had in our maxillary premolars when we had the [inaudible] a lingual root. But on the buccal surface we usually have two roots. And these are termed by the area they are located at. We have a mesial buccal root and a distal buccal root. Now where these 3 roots join we have area which we are now calling a trifurcation meaning three roots joining. We called it a bifurcation when we had 2. Now we’re calling it trifurcation or sometimes abbreviated furcation, meaning division of roots but this is a trifurcation.  The actual shape of these roots I think is important for many reasons. Not only from endodontic standpoints but also from surgical standpoints, periodontal stand… many reasons. Our lingual root is usually the longest root on this tooth. It’s a single root supporting the lingual half so it’s little larger and longer than our buccal roots. And has a [inaudible] tendency to be round in its overall structure. It’s the large, round type root. Our mesial buccal root is rather a broad, flat root. This is more similar to our roots on our mandibular incisors. It’s kind of a ribbon shaped broad flat root. And actually occasionally you will have a concavity down the center of it. It’s so broad and flat on this mesial surface and very frequently it will have a concavity on the distal surface of these mesial buccal root, right down on the inside in here. And this becomes rather significant when you’re trying to remove this tooth because this really locks into some bone there and becomes quite a problem.

Our distal buccal root is the smallest root and it’s kind of in between. It’s not really round and it’s not really flat and has a tendency to be a little bit on the broad side towards the occlusal but it has a tendency to round off as it gets down towards the apex. I really should say cervical. It doesn’t really come close to the occlusal. Usually referred to the cervical portion of the root here. Make sure I get my terminology straight here too. We have one section of this root here that we should’ve pointed this out on our premolars. Before the roots trifurcate here or bifurcate which is called the root trunk. That’s actually a new term for you. The root trunk is that portion of the root before we get a division. We have a root trunk. Actually if we go back and look at our occlusal outline on this tooth, this is often referred to as being rhomboid in shape. Mesial distal surface are somewhat parallel but not necessarily at right angles to the buccal and lingual surface. And we’ll make a drawing of this or if you make a drawing of it I should say we can make this rhomboid basically in its shape. That’s what they referring to. One other prominent characteristic I think we should point out to this and that is that even though we have four rather distinct line angles, our buccal line angles are more prominent or I guess you can say sharper. A little bit sharper than our lingual line angles which have a tendency to round more. We have one line angle which rounds very sharply as it gets toward the cervical. And this is your distal buccal line angle. Right as it gets to the cervical it becomes very rounded. In fact as the whole tooth has a tendency to tuck in in this area and this again becomes quite a problem in restorative and periodontal [inaudible] and should be noted. We had this present on the distal cervical area of our mandibular laterals and cuspids. We’ve pointed this out. For this rounding occurs very sharply and prominently on the cervical third of the distal buccal line angle area here. Sometimes this tooth is referred to as having a fifth cusp. When we have a fifth cusp present it kind of joins is and grows with the largest cusp on this tooth which we indicated to you as what? Mesial lingual being the largest cusp. Sometimes we’ll get an additional cusp which will occur in this area right here and I have a few of them. Sometimes it’s not present at all as in this tooth. And it can be present in varying degrees here. Again we find none here. It’s being our mesial lingual here. We find a small crevice right in here which indicates a very tiny cusp development.

Here this is getting just a little bit larger. Here our cusp has gotten so large that we’re actually creating a pit between the mesial lingual cusp and this fifth cusp. In this one you can see we have a very large fifth cusp and again a deep pit. I find that this pit frequently has a tendency to become carious and actually requires a separate restoration right in this pit that occurs between the mesial lingual and this fifth cusp. This is usually called just a fifth cusp or it could be called a cusp of Carabelli. It seems to be a jingling term that has gotten quite a lot of popularity. Cusp of Carabelli or just plain fifth cusp. Not always present and it’s rather highly variable in its amount and degree in size but generally always occurring when it does appear on this mesial aspect of this mesial lingual cusp. One thing we could point out to you also is our contact areas. Sometimes on these molars they start to become rather prominent and often times they will stain quite dark. And this becomes a problem occasionally when you lose the deciduous teeth that are in front of these and parents look into mouth and find a dark contact area and they rush Johnny in because he’s got a cavity. And you get to checking it and you find that it’s hard and stained and it’s just simply a contact area that has become stained. Here again we got a contact area on this tooth right in here that has stained up a bit. Notice how this calculus is collecting here. Notice where that is. It has a big tendency to collect there. That’s where we get that tremendous rounding of that distal buccal line angle right in the cervical. Very prominent area for calculus to collect because tooth just takes a sharp dip in that area. If we go to our 2nd and 3rds we’ll do more of a comparison study here, maybe pick up a few additional terms on it. We have differences in size and within the same mouth this becomes most important. This difference in size is about a millimeter in mesial distal width within the same mouth and our 2nd molar. And within the third molar, well, this can vary. Again about a millimeter smaller than the second [inaudible] in the mesial distal width. But this third molar becomes so variable and is so highly irregular and sometimes not even present. We are not going to spend too much time in studying this.

We’ll give you a little bit of information identification of it but we’re certainly not going to spend the time on it that it justifies in relation to the amount of a variations it has because it’s got a thousand and one variations. Our second molars are usually fairly characteristic in their occlusal anatomy. They are fairly sound in their anatomy. We have about the same width from the mesial to the distal, pardon me, from the buccal to the lingual as we do in our first molar within the same mouth that is. But we’re a little shorter on the mesial distal dimension as I indicated about a millimeter. We still have the basic rhomboid shape in it although our line angles, and particularly on the buccal here, are becoming rounded. Remember this was a characteristic between the first and second premolars. Our second premolars started to get quite  a little rounding in the line angles while our 2nd molar does the same thing in comparison to first. It just starts to round out in our general anatomy. In our anatomy occlusally again it’s not quite as sharp and distinct and prominent as was our first molar. That’s the same basic characteristic between the second and first premolars.

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