So today we're going to be talking about premolars. Premolars are essentially just an intermediate between canines and molars. So the first premolar, so the premolars are named mesial to distally just like molars are. So the first premolar is going to be the one that's closest to the canine and the second premolar is going to be the one that's closest to the molar. So the first premolar is more similar to the canines.
They're sharp and they're better for ripping whereas second premolars are more flat and they're better for grinding similar to what molars are. They erupt around 10-12 years and like all of the permanent teeth, the roots, the finished developing around two and a half years after eruption. They're often called bicuspids, but that's kind of a misnomer because the mandibular second premolar can have three cusps, which you'll see later.
So start off with the maxillary first premolar. So it's going to have two roots, whereas the other premolars are more likely to have, either only have one root or less likely to have two roots. So the maxillary first premolar almost always has two roots.
It's different than mandibular molars in the sense that the maxillary first premolar, the roots bifurcate in the middle or apical thirds. So farther apically down the road, the root is where it's going to bifurcate, whereas mandibular. mandibular molars is going to bifurcate either in the cervical third or the first half of the middle third. So maxillary first premolars, two roots, bifurcates farther apically than mandibular molars. Because it has two cusps, they're going to have two pulp horns and two root canals, one for each root.
And then... We'll see soon that it's going to have a longer mesocuspal slope than distal cuspal slope. So in the canine video, I mentioned that all teeth except primary maxillary canines and maxillary first premolars are going to have a longer... shorter mesial cusp slope than distal cusp slope, we'll see here that this is one of the exceptions to the rule.
And it's the only tooth that will consistently have a deep mesial crown concavity. So we'll see that again soon. So let's start off with the buccal view. So remember here that the premolars are now posterior teeth whereas canines are anterior teeth. So we're going to say buccal instead of facial but occasionally I'll probably say facial accidentally but I really mean buccal.
So let's start off with the buccal. Buckle view, as you can see here, looks very similar to a canine. You can only see one cusp because the lingual cusp is a little runt and you can't really see it. So buckle view, you can see one cusp looks similar to a canine.
It's going to have a crown that's slightly shorter than a canine. And we can see the buccal cusp develops in two, or three developmental lobes. You can see the two developmental depressions here. So we're going to have a middle lobe, a mesial lobe, and a distal lobe.
So that's significant because the lingual lobe is only developed from one lobe, which is why the lingual cusp is much smaller than the buccal cusp. So the buccal cusp has three lobes which it develops from. So we'll see here that the mesial cusp slope of the buccal cusp is actually longer than the distal cusp slope.
And that is the exception to the rule that the mesial cusp slope is always shorter than the distal cusp slope when you have one facial cusp. And the other one that is an exception to the rule is the primary maxillary canine. So maxillary first premolar and the primary maxillary canine is the exception to the rule for mesial cusp slopes and distal cusp slopes. Moving on here.
we see as we mentioned the lingual view the lingual cusp is smaller than the buccal cusp and because of that when we're looking at lingually we can actually see both cusps whereas in the buccal view we can only see the buccal cusp and the lingual the lingual cusp is shorter mesio distally as well as cervical occlusal cervical e and when we're talking about embrasures we said the facial embrasure is always thinner than the lingual embrasure because a lingual side of tooth is thinner than the facial side of the tooth. So that's pretty obvious here. The lingual side of the tooth is shorter than the buccal or facial side of the tooth, which is why when we do lingual abrasures, they're going to be wider. Moving on max a first pre molars in the mesial and distal view or in a proximal view So let's start off with the mesial view right here.
This is going to be distal So one of the things we're going to have is a mesial marginal groove Which right over here you're not going to see that in the distal Another difference between the mesial and distal is the developmental depression that we're talking about It's going to be in a crown right over here, but also extends over to the root, but this shaded area area right here is the prominent developmental depression on the mesial side of the tooth and this is not just developmental variation but this will happen in pretty much all maxillary first premolars and the only other tooth with a crown depression like this is going to be the maxillary first molar, and that's going to be on the distal side of the crown. But mesial developmental depression is for maxillary first premolar. You're not going to find that on the distal side of the maxillary first premolar, so that's another way to differentiate between mesial and distal. And that distal marginal ridge right here is going to be more cervical than the mesial. You can see here it's more cervical than the mesial marginal ridge.
So the cusp tips are going to be centered over the roots. So if you draw a line like that, sorry, but pretty much the tip of the cusp is pretty much going to be in center with the long axis of the root. So this is actually pretty poorly drawn, but you kind of get the gist of it. So something I want to clarify is the difference between a marginal ridge and a cusp ridge.
So this was less, I guess, prominent in anterior teeth, but as you go to posterior teeth, when we have a very complex occlusal anatomy, it's very important to differentiate between a mesial marginal ridge and a mesial cusp ridge. Right here is the buccal cusp. We see that it's bigger than the lingual cusp. So on the mesial side of the buccal cusp, we're going to have this right here, which is the buccal cusp ridge. Or the mesial buccal cusp ridge.
And then right over here, we're going to have... the mesial marginal ridge. So you can see that they go almost in different orientations and this is going to be like the ridge on the mesial surface of the tooth whereas the cusp ridge is going to be the ridge that goes up to form the cusp tip.
So we'll see that again in the cruzal view and then but I just want to make sure you know the difference between marginal ridge versus cup ridge because they are not the same. So, occlusally, this is pretty much a complete labeling of everything on the occlusal, so this is going to be, hopefully, after this session you'll be able to understand all of this. But we're going to start with this step by step. So, first things first, it's got a hexagonal shape, so we can kind of see that here. Looks like it's almost like a hexagon.
So let's orient ourselves. We see right here this is buccal cusp and this is lingual cusp because the buccal is bigger mesio-distally than the lingual. And so right here is a pretty good view.
If you had two of these side by side and you had to draw the embrasures, you can see here that because the lingual is shorter mesio-distally, that the embrasure angles are going to be much wider lingually than they are facially because here you can see it's much wider mesio-distally on the buccal side. So just a way to remember that the lingual embrasure is going to be wider than the buccal embrasure because the lingual side of the tooth is thinner mesodistally than the buccal side. So let's move on to the occlusal anatomy. So I want you, I think this is a good time to have a 3D tooth or a, you know, like a typodont or something because this is a 2D image of a 3D anatomy so it's not going to be the best picture to see a lot of things. So I want you to have a 3D image of a 3D anatomy.
things but I'm gonna it's probably the best picture I've seen so far it's from Wheeler so I'll just gonna work with it so let's start off with the cusper ridges so this looks like a really fat list but just remember that everything that happens on the mesol side is probably gonna happen on the distal side everything that happens buccally it's probably gonna happen lingually so if you kind of break this into quadrants there's actually not too much to see in one quadrant and then so when you go to this side it looks like a lot just just because you're doing the same thing, but you're multiplying it by 4, because everything you have on the mesial side, you're going to have on the distal side. Everything on the buccal, you're going to have on the lingual. So let's just start off with the cusp ridges.
So this is going to be this is why I think you should have the 3D tools, because actually, this is not the tip of the cusp. The cusp tip is coming out of the screen towards you, right over here. So right here, so this is mesial, this is distal, this is buccal, and this is lingual, right?
So this here is going to be the mesial cusp ridge and this is going to be the distal cusp ridge. And remember this is on the buccal cusp so this is going to be the distal buccal cusp ridge and this is going to be the mesial buccal cusp ridge. And then where they intersect is going to be the tip of the buccal cusp.
So this tip is coming out towards you. You can see that here also, this is the lingual cusp, so right here is going to be the mesiolingual cusp ridge and this is going to be the distal lingual cusp ridge and wherever they intersect is going to be the tip of the lingual cusp. So that's pretty standard.
I want to draw the marginal ridges on the same side so that we can see the difference. So while these cusp ridges are coming at you through the screen, occlusally the marginal ridges are going to be in the same plane as the screen because they're not coming occlusally but they're just going they're just on the distal surface right here so this here is a distal marginal ridge and this is the mesial marginal ridge and remember that the distal marginal ridge is is more cervical so it's actually technically into more into the screen than the mesomarginal ridge but you can't see that on the clues of view whereas you can see that here the distal marginal ridge is more cervical than the mesomarginal ridge so let's continue so we really got this we got this and we got this right so let's talk about the fossa's so purple right here So purple over here, this is going to be the mesial triangular fossa and the distal triangular fossa. So a fossa, as we know, is a depression, a 3D depression though. So the way it's actually going to look is if we were to draw a triangle shape like this, With the marginal ridge being the distal wall and then your buccal cusp and your lingual cusp as the other wall, this right here is going to be a 3D piece.
pyramid triangle shape. 3D triangle is a pyramid. Yeah, so this 3D depression is going to be the triangular fossa. And since it's on the distal side, it's going to be the distal triangular fossa.
And you can do the same thing here. It's going to be using the lingual cusp and the buccal cusp. And then...
And then pretty much this wall of the mesial marginal ridge wall, you're going to see this 3D pyramid almost shape triangle. This is going to be the mesial triangular fossa. And again, it helps when you have a 3D tooth to actually see this whole fossa.
So we'll just figure that. So the BTR and LTR, so that's going to be the buccal triangular ridge and the lingual triangular ridge. And it's not very, you can't actually really see, I mean I can't see it on this picture, but it is there.
If you had to type it out, it would probably be there too. But it's much more prominent in the mandibular first premolar, so we'll definitely revisit that again so you know what I'm talking about. But for now, the buccal triangular ridge, so it's going to be on, so a triangular ridge, is going to extend from the central groove here to the cusp tip. So the buccal triangular ridge is going to go from the central groove over to the cusp tip of the buccal and then the lingual triangular ridge is pretty much going to do the same thing.
It's going to go from the central groove over to the lingual cusp tip. And then so this is going to be the buccal triangular ridge and it's going to be the lingual triangular ridge. And so the The intersection of the two triangular ridges is going to form one of two things.
Either a transverse ridge or it's going to form an oblique ridge. So for premolars we're mostly going to see transverse ridges and then for molars we're going to see both oblique and transverse ridges. So what's the difference?
A transverse ridge is going to be 90 degrees. So this 3D wise, the buccal triangular ridge is going to be 90 degrees. and the lingual triangular ridge is going to intersect in a 90 degree angle and that intersection is going to be called a transverse ridge.
Whereas in if it's not 90 degrees then it's gonna be called the oblique ridge and that's something we'll see when we talk about molars. But until then again you can't really see in this picture so I'll mention triangular ridges again when we get to the mandibular premolars. So grooves, we all know what a groove is. It's just a nice line and indentation. I'll draw it from here.
So right here we can see the central developmental groove or the central groove. is in the middle right here. So mesial buccal developmental groove. Mesial groove on the mesial side of the tooth towards the buccal cusp. Right here is the mesial buccal developmental groove and the same thing on the distal developmental groove.
Distal buccal developmental groove. And then the mesolingual developmental groove and the distal lingual developmental groove is going to be pretty much the same thing only on the lingual side. So mesolingual developmental groove and this here is the distal lingual developmental groove.
So the difference between a pit and a groove is a pit is a point it's going to be like a point depression at the intersection of more than one groove. So right here we're going to have a distal developmental pit and a mesial developmental pit. Yeah, so the mesial developmental pit is just going to be the intersection of the mesial grooves and the distal developmental pit is going to be the intersection of the distal developmental grooves.
So as you can see, it's actually not that bad. It just looked like a lot because it's all on one tooth. But if you just remember, if we just had one quadrant drawn with the quadrants being formed by the triangular ridge here, your cusp slopes here, or the cusp slope, the central groove, you have a developmental groove, and your mesial marginal ridge. That's pretty much the anatomy that was shown right here. but in all quadrants.
Oh, I guess also the pit right here that I forgot to mention. But see, it's actually not that complicated. Just this times 4 and you'll get the entire occlusal of the occlusal anatomy of the max-wave first premolar. Moving on to maxillary second premolars, there's not as much talk about them there. They're pretty much similar, very similar to the first premolar, so we're mostly just gonna talk about the difference between the two.
So there's actually a lot of anatomical variation in the maxillary second premolar, much more than the first premolar. So sometimes you'll see that the crowns are bigger than the first premolar. Sometimes you're gonna see that the crowns are smaller than the first premolar.
So I don't think it's a rule to say that the crown is bigger than the first premolar, which some people say it was, just because you have more variation with the second premolar. Something that's more common that you're gonna see is that the maxillary second premolar, the crown is gonna be less angular, or in other words, flatter, and it's gonna be more rounded. So pretty much it's gonna look more like a molar than a canine as the maxillary first premolar was.
So the second premolar, it usually has one root, but it can have two roots also. So pretty much one or two roots. But even if it has one root, a lot of them, like about half of them, are still going to have two canals within that one root. So let's just move on.
So the buccal view again, it looks similar to the maxillary first premolar, so it's going to look similar to a canine in the sense that when you look at a buccaly, you can't see the lingual cusp. But, so the difference between the maxillary second and the maxillary first is that you're... So this is no longer an exception to the rule.
So the mesial cusp slope is actually going to be shorter than the disal cusp slope. You can't really tell as well in this picture because they're almost equal, but generally it's going to be slightly shorter than the disal cusp slope. And it's going to have a rounder cusp tip than the first premolar.
And when we look at it lingually, we'll see that the lingual cusp is actually not as small as the... Compared to the buccal cusp, they're almost the same size. It's still slightly smaller, but much less so compared to the maxillary first premolar. And you can see that more right over here actually.
In the inner proximal view, we can see here that the cusps... The buccal cusp here is pretty much almost equal to the lingual cusp. It's slightly taller. Mesodistally, sorry, buccalingually, it's slightly thicker, but you can't really tell.
It's not as... prominent as the difference is not as prominent as it was in the max a first premolar so the mesial side we're not going to get the the mesial marginal groove that we had in the max a first premolar right here we're not going to have a very prominent depression in the crown. You might have a depression in the roots, but in terms of the crown you won't have that prominent mesial development depression.
Other than that, it's pretty similar to the maxillary first premolar. The main takeaway is the lingual cusp is not as small. It's almost the same size as the buccal cusp whereas in the maxillary first it's very different.
Occlusally, it has an oval shape more than a hexagon shape, and it looks wrinkled. And the reason for that is you're going to have a short central groove and a lot of supplemental grooves. Whereas, remember, in the maxillary first premolar, we have...
had a long central groove and the only supplemental grooves we had were the mesial, buccal, mesolingual and on the other side the distal, buccal and the distal lingual. Whereas here this thing's got grooves everywhere. So I'm not even going to start talking about the anatomy just because there's so many developmental grooves they don't really have names. So main takeaway, short central groove, lots of supplemental grooves, which makes it look like a wrinkled thing that you don't want to memorize.
So mandibular first premolars. So some things about a mandibular first premolar. It is a smallest premolar.
It's going to have the narrowest and smallest roots of the shortest roots of all the premolars. They're typically going to have one root and usually only have one root. one canal but 30% ish will have two canals so not as much as a max rate second which is almost half so this is about 30% and as we said earlier it's going to have most prominent transverse ridge so hopefully after looking at this occlusal view we'll know what transverse ridge really looks like. It is the only tooth with that mesiolingual groove and the only tooth with the MMR at a grossly different angle than DMR.
So not to get confused with the mesiomarginal groove in the max-ray first premolar, so I'll show you when we get to the interproximal view. So let's start off with the buccal and lingual view. So again, on the buccal view, because the lingual cusp is shorter than both mesiomars. mesiodistally and occlusal apically than the the sorry the lingual cusp is shorter mesiodistally and occlusal apically than the buccal you can't really see the lingual cusp on the buccal view however the on the lingual view you can actually see four surfaces you can see both the mesial surface here you can see the distal surface here you can see the occlusal surface and the entire lingual surface of the crown from the lingual view and the reason for that is is as you move lingually, your crown is going to taper lingually.
So it's going to get shorter mesodistally drastically as you move more lingually. So right now, and because the lingual cusp is drastically shorter than the... buccal cusp you can practically see a lot of the occlusal anatomy. So that's something that's very noticeable with the mandibular first premolar, whereas the other ones, even though you had a short lingual cusp, it wasn't as skinny mesodistally and occlusal apically it wasn't as short. Sorry about the sirens.
But yeah, so that is something that is more unique with the mandibular first premolar. So... mesolingual developmental groove separates the mesial marginal ridge from the lingual cup. So right here you're going to see a deep developmental groove on the mesolingual side and it's pretty similar to the mesial marginal groove on the maxillary first premolar.
The difference is this is going to be much deeper, so much so that it's actually completely separate the mesial marginal ridge here from the cusp ridge here. So let's say the cusp ridge goes like this. Now your mesial marginal ridge is going to look like that too.
And so it's going to be this groove right here is going to completely separate the mesial marginal ridge from the lingual cusp. And because of the mesial marginal ridge now, going down cervically as you move lingually it's going to be at a totally different angle than the distal marginal ridge here and that's what it means by the mesomarginal ridge, it's a different angle than the distal marginal ridge in approximately So again we're going to have the developmental groove. This picture isn't as good. Some pictures you can actually see this huge valley of developmental groove and that's immediately very easy to separate.
the difference between the mesial side and the distal side is because of that developmental groove. So the tip of the buccal cusp right here is going to be centered over the long axis of the root. And then the lingual tip of the cusp is going to be in line with the lingual aspect of the root right here.
And so that's pretty much what you'll see in a proximal layer. There's not that much more. You might have some crown concavity here on the mesial side, but it's more of a variation than a strict rule, whereas a maxillary first premolar, you're always going to have a very prominent developmental groove on the mesial side. And the distal marginal ridge is going to be... Sorry, the mesial marginal range is going to be more cervical than the distal marginal range, as you can see, because this goes down cervical.
The distal marginal range is more occlusal, the mesial marginal range is more cervical, and the distal marginal range is going to be more... Developed because you don't have that Developmental groove that's going down So in the Koolso view There's gonna be a lot of variations. So it's tough to say what one's gonna do the other I Mean you guys look at here.
This thing looks nothing like this and partly because, I mean, honestly this picture just blows, so sorry, wheelers, but your wheeler certainly has pretty good pictures, but that one, I don't, that doesn't look like a tooth. But let's use this picture right here. So one of the main things is going to have prominent triangular ridges, and because of that, it's going to have the most prominent transverse ridge out of all the premolars. So again, what is a triangular ridge? So we talked about this in the occlusive view of the max-ray first premolar, but it's going to go from from the central groove up to the tip of the cusp.
So in the buccal triangular ridge, we're going to see right here from the central groove up to the tip of the buccal cusp, we're going to have this elevation. So this is going to be, you can tell from the shadows here that this is coming up. So this elevation here is the buccal triangular ridge. And so the triangular ridge is more prominent in the buccal than the lingual side. but you can still see in the lingual side.
Right here, the tip of the lingual cusp to the central groove, central groove to the tip of the lingual cusp is going to be your lingual triangular ridge. And where they intersect is going to form a transverse ridge. And you can see because it forms almost like 90-degree above, the 90-degree intersection of the two triangular ridges is going to form a triangular ridge.
transverse ridge. So what that is going to do is it's going to separate mesial from distal. So if you get a question what does the transverse ridge of the mandibular first premolar separate, it's going to separate your mesial pit here from your distal pit because that's essentially going to be like your midline. So other than that, there's not too much else to know. We have the mesomarginal ridge curved cervically.
You can kind of see that here because you're going to have the mesolingual developmental groove right over here. So this is like a valley shape. You almost have like a little mini embrasure here. because of the mesial lingual groove.
So your mesial marginal ridge is going to curve cervically down. And then the lingual cusp ridge is also going to curve down that way. And other than that, that's pretty much what you need to know for the mandibular first premolar. So mandibular second premolar.
So... This is the only premolar that can have three cusps. and that is why a bicuspid is technically a misnomer for premolars. They're pretty much going to be bigger than mandibular first premolars. It's pretty much transition from the first premolar to the molar so again similar to the maculary single premolar they're going to be a little bit flatter less angular because it's going to look more molar like than they are premolar more molar like than they do canines.
premolar most likely to be congenitally missing, third overall. So remember, your third molar is going to be the first for congenitally missing, your maxillary laterals are going to be the second, and your second premolar is going to be third. The premolar is most likely to have a central pit. The premolar is most likely to have one root and one canal. So remember the mandibular first premolar, like 30ish percent, might have two canals.
Your maxillary second premolar, like half of them have two canals. And your maxillary first premolar have two roots and two canals in pretty much all of them. So...
Let's start off again with the buccal view and the lingual view. So the mandibular second premolar, in comparison to the first premolar, it's going to have a shorter buccal cusp and a taller lingual cusp with the first premolar. Actually, you can see right here, it's going to have, this tooth has two lingual cusps because this is the three cusp type.
And... Just to help you differentiate it, this is the distal marginal ridge. This is your distal buccal cusp ridge.
And this here is your distal lingual. cusperid so this isn't like four cusps this is a cusp here this is a cusp here and this is a cusp there again because they are more molar like than the canines they are going to have rounder ladder ridges on the cusps and they're going to have two lingual cusps one or two lingual cusps so if it has two then you have one mesial one distal and the mesial lingual cusp is always going to be bigger than the distal lingual cusp so looking at it in approximately It's going to have a longer root than the first premolar, but it's going to be more blunted apex, so not as sharp. You're not going to have the mesolingual developmental groove like you had in the first premolar. most posterior teeth the crown is going to point lingually but this is very much more so than the max mandibular first premolar so this one points more lingually it's angled more lingually than the manual first premolar and a way to differentiate between the mesial marginal ridge or the mesial surface versus the distal surface is your DMR is going to be slightly more cervical than your Beazle marginal range. And so the clues of you.
Not to confuse you, but these are actually flipped. So this is mesial, this is distal. For this side, this is going to be mesial, and this is going to be distal, and then buccal-lingual. And the way I know that is because we said earlier the mesial-lingual cusp is always bigger than the distal-lingual cusp.
And so pretty much... The way that it's shaped in terms of the grooves is if you had a two cusp premolar, then you're not going to have this extra groove here that's splitting the two lingual cusps. So you're going to just have this red crescent shaped, whereas a three cusp is going to have a Y shape.
So you can see that right here. You have a Y shaped like this, but if you don't have this, then you'll just have a crescent. And we also mentioned that is the most premolar most likely to have a central pit. And the reason for that is a pit is formed by the intersection of at least two grooves, right? So right here, we're going to have a central pit.
Let's change colors. Because you're going to have your central groove, but you're also going to have your groove right here, the splitting between your mesiolingual and your distal lingual cusp. So that is why you can have a central pit with a mandibular second premolar. So that pretty much covers...
All the premolars. So I made this table just to help you differentiate between mesial and distal because that's typically going to be harder than buccal lingual just because the lingual cusp is typically smaller than the buccal cusp. It's so obvious which side you're looking at. Buccal lingually. But mesial distally sometimes it's more similar.
So I just made this table to help you. But yeah, so this will pretty much sum up the difference between mesial and distal. So most of them, the mesial side is going to have either marginal groove or developmental depression, which will help you differentiate between the two. But I hope this video helps. And I'm going to make one more video in this series, and it's going to be for molars.
So look out for that next week.