Maxillary Molars P3
2014
One other thing that starts to become rather prominent here is this distal lingual cusp. This entire mass starts to become smaller in overall dimension. And this groove that comes out, the distal lingual groove, as it crosses our cusp ridge here and starts to come down to the lingual surface, it doesn’t usually cross this height of contour on the lingual surface and we don’t usually get this deep groove crossing the height of contour. We don’t very often have any groove down the root here at all. Just comes down part way on the lingual surface and stops. It’s lost its characteristic prominence. Our buccal groove does carry on onto our buccal surface and carries down on the surface away but again isn’t quite as sharp and as deep and as prominent as it what would be on the first. I should make one comment in looking at these buccal surfaces here. Usually our buccal cusps, our both first and second, are approximately equal in size. Very similar in size being equal. Equal in their width as well as their height. And this buccal groove frequently will come right down the middle of the buccal surface. On the lingual we find that this is not true. Our mesial lingual cusp is usually about 2/3 width of our lingual surface, 2/3 the mass dimension and our distal buccal cusp is smaller.
Come to our second this occurs even more so. We may have three quarters of our lingual surface mesial lingual cusp. Maybe only one quarter our distal lingual cusp. And actually when we go to our thirds we’ll find out that frequently we have our entire lingual surface, maybe just this mesial lingual cusp or we may not have any or maybe very, very small distal lingual cusp area here. But one thing we also should note and that is when this groove does come down on the lingual surface by the time it crosses the height of contour on the first it’s usually pretty close to the mid portion of the tooth. It comes out at an oblique angle and by the time it reaches a height of contour it’s almost in the middle of the tooth. In our seconds this is not reaching the height of contour and we are not flattening [inaudible] our lingual root here. Lingual root is usually very round in this area as is our outline of our tooth because this groove just isn’t crossing. Our anatomy occlusally is basically the same as far as the terminology. We have all four of the same cusp, we have same surfaces, same line angles, same point angles, same marginal ridges with again mesial marginal ridge being closer to the occlusal, further the from the cervical, either way you want to put it. And our distal marginal ridge dipping closer to the cervical. One thing that is fairly characteristic about this oblique ridge in this tooth is that it’s not nearly as prominent in the second as we find that we’re losing a lot of our general overall prominency.
Often times this central groove will cross right through this oblique ridge. And this becomes important when we are restoring the tooth. We kind of like to know whether we want to follow that groove out or whether we want to stop on this sharp incline of our oblique ridge and very frequently this will cross right over the ridge into the distal pit, make a groove right through it. Our root structure on our second is usually contained within the crown and I didn’t really point this out too prominently in the first…let me show you difference here in existence….but within the first our root structure is said to be trifurcated very close to the crown and we have a short root trunk. In the second our trifurcation is not as close to the crown and we have a longer root trunk. In the first this lingual root in particularly usually extends well beyond limits of the crown. It’s much broader than what the crown is. In our second we usually we usually will see this lingual roots is contained beneath the crown, it doesn’t extend significantly out beyond the width of the crown. On the buccal surface of the first we find that the roots are trifurcated close to the cervical and that the roots are well spread. On the second these roots are generally not spread very wide. Sometimes they will be a little bit but certainly not as wide as they are in the first. Sometimes they’ll actually fuse and here we can see a fusion occurring in them. Actually a little bit of bone that was left in that fusion. This becomes a problem anatomically where our roots separate towards the middle portion of the root and then fuse again at the apex. Then when you try to remove these teeth you got a little piece of bone that grows right through this area and locks right in on it but they’re not nearly as widely spread. The root structure in general is shorter. But again our crown structure is shorter. If we compare these with our bicuspids we’ll find that a mandibular…pardon me…the maxillary first molar has a shorter crown. We just got done saying that the mesial distal dimension, buccal lingual dimensions are all greater but the crown height from the cervical line to the tip of the cusp is about a millimeter shorter than our bicuspids. And when we go to our second molars again our crown becomes shorter for half a millimeter or so. As we go to our thirds it becomes even shorter yet. But our root structure does start to vary rather significantly and this becomes rather important in relation to surgery, in relation to our building restorative restoration on these teeth because we like a nice, heavy, strong root structure to hold these restorations and bridges and partials and other structures into the mouth. Also becomes very important as far as periodontal problems. If we get infection down in this trifurcation area this is very difficult to control. We have to go a lot further down the root surfaces to get this in second premolar or second molar where as in first molar we got just a very short distance before a gingival recession and pocket formation [inaudible] before we get into this trifurcation. So frequently it’ll cause us quite a little difficulty.
One thing I should point out here as I see these rings of calculus. This is kind of a ring of hardened calculus on here and this is a ring of calculus on this tooth here…little soft tissue. We showed you some bone and what have you. One of the things that’ll occur on these teeth are little white lines like this and this isn’t a surface deposit of any nature. And if you were to take your explorers and go over these teeth you’d find that some of these little areas you can’t feel. They just feel completely smooth. What we have here is what is called a decalcification line. At one time when this child evidently was 6 probably 8, 10 years old, before the second maxillary molar came in, he lost his toothbrush for 6 months or something and we got a plaque formation and a generalized beginning decalcification of this tooth, right at the gingival line. This is evidently where the gingival line was at that time. And this has started to decalcify which is the first beginning stage of our decay. But evidently he found his tooth brush, gingiva tissues receded and it stopped at that point and never did become a problem not having gone any further. Our outlined form, at least from the occlusal, on our third molars is no longer referred to as being rhomboid. Because of the prominent lack of this distal lingual cusp and a very large mesial lingual cusp we pick up more of a heart shape. So frequently we hear the maxillary third molars referred to as heart shaped teeth. If you look at the inner occlusal on these…we’ve got couple of them sat here… we find that they are rather distinctly irregular. We don’t find prominent pits, prominent grooves, we get just a lot of accessory fissures what we call supplementary accessory fissures and grooves developed in all types of irregular directions. We have some of our characteristics still prominently present including our three basic cusps on this. On the lingual having mainly our just mesial lingual. We’ve got very little distal lingual cusp on this. Our marginal ridges are still present though. we got… and our central fossa is still rather prominently present. s to if we have any oblique ridge or mesial distal ridges…we certainly have very little of any distal lingual groove or no lingual groove down the lingual surfaces of tooth at all. We looked to the root structure on these teeth. We frequently find that they are often times becoming fused and that they can be separate or they can be fused. If they are fused you’ll find that there’s usually grooves in between where the roots should be.
This sometimes frustrates student because they have difficulty identifying maxillary mandibular unless the can count 1 or, pardon of me, 2 or 3 roots. When they’re all fused into one this creates a problem. We have basically the same type of a situation with a very broad, flat, mesial surface as we have this broad, flat, mesial root and on our distal we have this much shorter, smaller or rounded distal buccal root which is usually distinctly different than other roots on it. We’re not going to spend a lot of time as I indicated studying these third molars because of the large variation that does exist. Because really the lack of importance in the mouth and many times they’re not present in the mouth at all but you should be able to identify first and second rather characteristically and if we haven’t got a first or a second then we generally toss it into third category. If we look at the pulpal anatomy on these maxillary molars you can see that in order to get into the pulp chamber of these molars we need to place our opening into the central and mesial fossa. Here you can actually see the lingual root canal exiting out of the pulp chamber. This opening is actually mesial to oblique ridge. Actually I should mention that this oblique ridge sometimes is referred to as a transverse ridge. Technically it is an oblique ridge and on our examinations and the State Board examinations, national boards it will be ab oblique ridge but in common daily terminology occasionally it’ll be referred to as a transverse ridge. So if somebody talks about a transverse ridge in a maxillary first molar you’ll know that they are really discussing the oblique ridge. It’s kind of a interchangeable term. You can see the type of opening that is needed in this tooth. You can see some of the pulp canals starting under the basal chamber.
Let’s look at the cross section here. We have a mesial distal section of the tooth which shows our two pulp horns in this section. Actually this tooth has four cusps now so it’ll have four pulp horns. We got our mesial buccal pulp horn and our distal buccal pulp horn. Our pulp chamber, very well defined in these teeth and then our two canals. We have our…oh, let’s see…we got to get our orientation right here. I think I called this one the mesial buccal…it will be over here…is our mesial buccal pulp horn. This is our distal buccal pulp horn. Distal buccal is a little bit smaller. We’ve indicated that our two buccal cusps are usually of equal size. Actually the mesial cusp is usually a little bit larger and not a lot and certainly it doesn’t have the variation in size that our lingual cusps have on our maxillary first molar. So this is our mesial side. We have our mesial buccal pulp horn pulp chamber and our mesial buccal root. Usually this mesial buccal root will have a little bit of a gentle curvature towards the distal line whereas our distal root is frequently straighter. And both these roots are protruding towards the distal a little bit. These canals are basically rather narrow from the mesial to the distal. If we look at a buccal lingual section on this tooth we find that we can just see one of our buccal canals. And this is our mesial buccal one here.
This is the largest root, the flat one, quite wide from the mesial to the distal. As we indicated sometimes this will have a concavity. Occasionally in a small percentage of these this will actually be two separate canals but most of the time it’s just one canal which is a little bit broader from the buccal to lingual sine our root is broader. We have to remember our external morphology on it. Our lingual root which is usually the longest root although we’ve got the tip on this one broke off here, is round and our canal frequently is round in this tooth. And it’s usually the largest canal on the tooth. It’s also the largest root usually on the tooth. Our maxillary second molars are usually very similar in our mesial distal section. We’re sectioning through our two buccal roots here again. We got our two pulp horns which are prominent, mesial buccal and distal buccal. And we’ve got our chamber and our canals which again are very narrow from the mesial to the distal. In this instance we got a little piece of bone that actually came out and stayed with this tooth. As the apex of our teeth became closer together it kind of pinched off a little piece of bone right in here. We look to our buccal lingual section on our second and we should have identified our pulp horns or mesial buccal pulp horns since we’re going through the mesial buccal root here, mesial buccal cusp… this will just be our mesial lingual pulp horn. This is the largest cusp on the lingual. We have a mesial lingual pulp horn we’re actually sectioning through here. But again we’ve got our round, rather long, fairly good sized lingual canal, lingual root canal. Then on the mesial we got our mesial buccal root canal. And again there’s a possibility that this could be two separate canals on this tooth although we usually just have one. They usually will constrict just before they come out the apex of the tooth at the apical foramen on these.