Welcome to the University of Michigan Dentistry Podcast Series promoting oral health care
worldwide.
Let's briefly review our maxillary molars again starting with the first molar. This
is usually in about six, primarily a grinding tooth. We've got the largest occlusal table
on it of any tooth in the mouth. Frequently it's referred to as the most important single
chewing tooth in the mouth a six year molar or the first permanent molar. We will sometimes
call it permanent in contrast to the deciduous molars. Our first maxillary molar. We have
our four cusps on this, very characteristically. Each turned by the surface in which they're
located. We won't go over them specifically here now. We have sometimes have a fifth cusp
which protrudes or develops off the largest cusp on here on the mesial-lingual cusp. Our
two buccal cusps about even in size. Our lingual cusps. The mesial lingual being considerably
larger than our distal lingual which has a tendency to get smaller and fade out as we
go to our second and thirds here. Not a lot of new terminology per se in so much as we're
just surface orienting our pits and fossils and grooves and what have you. But we do have
this oblique ridge which we indicated to you ran from the mesial-lingual cusp to the distal-buccal
cusp. This being a very important ridge in this tooth. We do have our central pit surrounded
by the fossil. We do have a buccal groove. This just has one term it comes out straight
to the buccal and crosses down onto the buccal surface not crossing the height of contour.
This is all called buccal groove. On the distal pit we have a groove coming out to the lingual
and this groove has two terms really. When it's in the occlusal portion of it it's called
a lingual groove and when it crosses our cusp ridge here and comes down the lingual surface
it's called just the lingual groove so it can be called either the distal lingual or
the lingual groove. Kinda depending upon which surface it's prominently located on and this
frequently does cross the height contour of the lingual surface and oftentimes down onto
the root.
We've got the rhomboid basic shape but our other pits and grooves, fissures, mesial marginal
ridge, distal marginal ridge, our triangular ridges, our cusp ridges, we have to identify
them according to the cusps now. All are basically just turned to the particular cusp and surfaces
they're located on. Roots are three and have the terms according to the root surfaces are
located on. The largest root, usually the lingual root, and a big, somewhat rounded
character although the first has a tendency to flatten as this groove comes down here
and actually sometimes grooves right onto the root. Otherwise, basically a round are
all very flat mesial buccal root and our smaller, smallest of the three, distal buccal root
which is kind of cold and tucked under the crown a little bit more than the rest of them
and makes this distal buccal line angle very prominently rounded in the cervical portion
here like we had indicated. That should review your basic terminology. Let's look at some
of the differential characteristics between our first, second and third. One thing we
should identify here and meant to do this before and that is the term "embrasure". The
term "embrasure" refers to the area located between the marginal ridges and the contact
point. This is an area in which when you're chewing the food comes into this area and
then has to go out either to the buccal or the lingual. So we've got a, kind of a triangular
area bordered by the marginal ridges of our two adjacent teeth and the apex of our triangle
being the contact point. This whole area through here is termed an embrasure area. That is
a term that we should put into our vocabulary here now. If we look at the differential spotting
characteristics of these teeth we find that our first is generally a little wider from
the mesial to the distal and our second becomes a little smaller as does our third in the
mesial distal dimensions. Our first is rhomboid a little bit sharper on the corners. Our second
still is rhomboid but is started to become rounded a bit. Our first has a very prominent
strong oblique ridgeů traversing obliquely across the tooth. Our second oblique ridge
is not as strong and frequently is crossed by this central groove coming from the central
pit into the distal pit. Our first has a much larger distal lingual cusp and our second
distal lingual cusp gets proportionally smaller. Our first frequently has this distal lingual
groove and actually as it gets under the lingual, the lingual groove, crossing the height of
contour and coming down under the root portion of the tooth. Whereas in the second, this
generally lingual groove does not cross the height of contour of this tooth. It generally
stops and we do not have a groove on the root. The root is usually nice and round in this
area and doesn't actually flap into the groove. We have the differences of the root structures
themselves. The first one having a higher trifurcation or a trifurcation closer to the
crown. Therefore having a shorter root trunk. The roots being widely spread and particularly
this lingual root extending out beyond the width of the crown. Our second, our crowns
are usually underneath, pardon me, our roots are usually underneath the crown and our roots
are not as widely spread. Sometimes they actually become infused. Here's a mesialů broader
flap mesial buccal root that's fused with the lingual root of the distal here they're
still somewhat separate. But they do come down under the crown rather distinctly and
haven't got this groove here. Our third molars are difficult to characterize because they're
so variable. We generally say if we haven't got first or second characteristics then there
will be a third. The third's generally more heart-shaped, more irregular in its crown
anatomy, occlusal anatomy, having a very small, if at all, distal lingual cusp. One of the
things that has formed in these is if we find that we have a contact point such as what
we're showing along in here, on the distal of a tooth then we know it's a second. Certainly
couldn't be a third if we had a contact point on this surface. So occasionally somebody
will come up and say this is a third molar, isn't it? And we'll look at it and find a
real distinct contact point we know that it has to be a second even though the other characteristics
will vary towards a third. It's a gradual gradation from tooth to tooth as these changes
occur and there's no characteristic that you can say outweighs or is more important than
the other characteristics. Characteristics I think are probably most important are the
oblique ridge, this lingual groove, the size and squareness of our crown, and our actual
root being the last main characteristic as far as its being under the crown or extended
out beyond the crown and the height of the trifurcation in relation to our cervical line.
I don't think you should have a great deal of difficulty distinguishing these if we kind
of toss out and don't concentrate on distinguishing our third molars, we've tried to, in the teeth
that we're furnishing to you eliminate most of the third molars. These are the ones we
always get sent to us in great numbers. In fact, as we got just gallons and gallons of
third molars in our tooth room but we tried to separate them out and give you just mainly
first and seconds with a few occasional thirds so that you don't spend a lot of time studying
the very highly irregular teeth whose roots often fuse on them. Let's outline these a
little bit in sketch form here. One of the things I think we should be able to do is
to sketch these teeth.
And the occlusal anatomy becomes fairly distinct in these teeth. If we were to sketch a maxillary,
say, first molar, the first thing we'd want to do is identify the central pit. The central
pit is almost exactly in the center of the tooth. We'd also have a mesial pit. And a
distal pit. We'd have a groove connecting up these two but not necessarily the central
and the distal because of our oblique ridge. Let's identify some cusps here. We have a
mesial buccal cusp and a distal buccal cusp. Approximately evenly oriented in their segments
and these are separated by our buccal groove. It comes straight out the buccal surface not
at an angle but straight out the buccal surface down onto the buccal but not over the height
of contour. So this separates it fairly evenly on the buccal surface. On our lingual surface
we've got two cusps. Our mesial lingual is not directly in line with our mesial buccal.
Actually, it's a little bit to the distal and a little bit towards the center. So we
may expect to find it along here but actually, but it's a little bit towards the middle of
the tooth and a little bit more towards the distal. It's the largest one of all of them
not only in mass but in height. Our distal lingual being the smallest located in the
area here. We've got one other very prominent groove in this tooth. And this is our distal
lingual groove which comes out and actually comes at an angle comes over and comes down
our lingual surface to the point that it crosses the height of contour so that if you look
at this tooth you'll find an actual dipping in the outline form of the tooth right here
where this is crossing the height of contour. We would hope that you'd be able to identify
that. Now we've got our oblique ridge. This is something that is frequently confusing
to students because they like to draw the oblique ridge right straight between our mesial
lingual and our distal buccal cusp and it doesn't go right straight across. It actually
comes off and goes rather significantly towards the distal of the tooth before it traverses
over to the distal buccal cusp and it kind of divides our tooth into a mesial two-thirds
and a distal third so it's not sectioning right through the center of the tooth. It's
going toward the distal and dividing it into a mesial two-thirds and a distal third. We
may have grooves that will come up just a little bit but they generally don't cross.
Occasionally we have a little groove coming out the mesial pit and up to our mesial marginal
ridge. The mesial groove, the mesial marginal groove. But not real characteristic. Now if
we were to take in and draw our marginal ridges on this. We'd find we have a mesial marginal
ridge,
our mesial buccal cusp ridge,
distal buccal cusp ridge,
distal marginal ridge,
distal lingual cusp ridge,
mesial lingual cusp ridge,
and this gives us our occlusal table. Basically the area in between our cusp ridges, marginal
ridges would be the occlusal table of the two. We could also continue to identify some
grooves, some ridges on it. The most prominent ridge beyond this is our mesial buccal triangular
ridge. It comes down into this central groove here. This is probably the most prominent
of our triangular ridges. Actually coming into the central area of the tooth. Our triangular
ridges here are kind of connecting up into our oblique ridge and actually I guess that's
fairly prominent but we're not calling this a triangular ridge anymore it's an oblique
ridge. Our triangular ridges are mesial buccals certainly the strongest. But basically speaking
the things we would be looking for in an outline sketch of this is that we have the rhomboid
shape of the tooth. Our sides here are somewhat parallel but not at right angles to our buccal
or lingual surface. We got basically a rhomboid or square tipped to the side here a little
bit. We've got our central fossil right in the center of the tooth. Buccal groove coming
straight out the buccal surface but not crossing the height of contour. Lingual groove coming
out obliquely, cross would be distal lingual and lingual, coming out obliquely crossing
the height of contour. We expect a buccal cusp to be the same size and approximate location
in proportion to the mass of the tooth. We'd expect to find our lingual cusp to be the
largest and not located directly opposite our mesial buccal but a little bit towards
the center and distal. So this gives you basic ideas on our occlusal anatomy. Now you may
say, why so much talk about occlusal anatomy? Well, these teeth, we get involved in restoring
the occlusal anatomy to a rather significant extent. And these are old amalgam restorations.
They've tarnished with age and turned rather black. But quite frequently we're required
to replace this anatomy with amalgam restorations in a matter of five minutes or less which
means you have to carve back the entire occlusal anatomy in five minutes or less. So you've
got to know exactly where that central fit goes, exactly where the grooves are going
to be, and know it so well that automatically you go right to it and put it into shape rather
rapidly. We're using wax in the laboratory now and I don't think that any of you are
going to produce a quality wax carving in five minutes but when we get to our amalgams
and in a mouth of this size they have to be done in five minutes. Now obviously these
are extremely poor. And many of those that you find in the extracted teeth are extremely
poor and that's probably one of the reasons why they're in the extracted teeth because
the overall quality of dentistry has been so poor that these teeth just you know, didn't
make it. And this is not always the patient's fault. It's sometimes the fault of the dentist
not being capable of producing anatomy and if they don't know it then certainly they
can't produce it. We looked at this piece of jaw bone that had the posterior teeth here
in it a while back but you might just look at this in relation to the overall outline
form of these teeth. As far as the rhomboid nature particularly of this first molar, it
worn rather significantly on the occlusal but it's a rather sharp rhomboid outline.
Notice how this second is starting to round and it's getting a little smaller in its mesial
distal dimension, buccal labially about the same. Getting a little smaller mesially distally
but it's still has the basic rhomboid nature. Our third smaller yet and because of our smaller
distal lingual cusp it's having a tendency to become on the heart-shaped form. But within
the same draw you can get the idea of the different teeth. Very frequently we're called
upon in the mouth to identify these molars by looking at their occlusal anatomy because
this is basically all you see on them is their occlusal anatomy and if one of them is missing
or if only one is present you have to kind of figure out which one is which. Basically
our crown length is totally shorter than our bicuspid length and it gets continuously shorter
as we go to the posterior. Actually, our third molar crown length is almost two millimeters
shorter than our bicuspid length. We have broader dimensions in some areas but shorter
dimensions in the total crown length. The crown is short and fat but they're getting
broader in their mesial distal buccal dimensions and shorter occlusal cervically. Well we made
you take a quiz here this morning, we made this review rather brief. We spent time on
our original lecture here this morning.
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