Dental Anatomy | Occlusal Contacts | INBDE

[00:00] This video is sponsored by BootCamp.com. Check it out for INBDE prep and use coupon code mental dental for 10% off. Hey everyone, Dr. Ryan here and welcome

[00:20] back to our dental anatomy series. This video is entitled occlusal contacts. But first, I want to talk about biology. A core tenet of biology is the relationship between structure and function. At this point in our dental anatomy...

[00:40] anatomy series, we've covered the structure of every single permanent tooth in the mouth. And that's awesome. So now it's time to talk about how those teeth function together. Since the teeth function in

[01:00] three dimensions. There are three planes that we need to be familiar with. The first is the coronal plane, which if we go over to our diagram, that refers to this plane going from left to right. So coronal, this

[01:20] word comes from the Latin word for crown. So imagine this person, this patient, wearing a flat paper crown or like Mickey Mouse ears on top of their head. That crown or those ears would

[01:40] being the same plane as the coronal plane. So that's how I remember that one. The axial plane is shown here and this is a horizontal slice or a horizontal plane that splits into a superior half and an inferior

[02:00] For this one, I imagine a woodcutter wielding their axe chopping down a tree, and that axe is hitting the tree in a horizontal manner, the same plane as the axial plane. And lastly, we have the sagittal

[02:20] plane. This one is shown by this front to back plane. Now the word sagittal comes from the Latin word for arrow, and you may be familiar with the zodiac sign sagittarius, who is an archer. So, imagine

[02:40] sagittarius firing an arrow at this person's forehead, splitting it into a right and a left half. And sorry, it's kind of an aggressive metaphor, but hopefully all of these things help you remember the three planes. We have a crown, a

[03:00] wood cutting acts, and a bow and arrow, all of the memory tools that you need to remember those three planes. So let's start with the coronal plane, and this is a coronal slice through the back of the patient's mouth, showing just one half of the mouth of course. This is

[03:20] is the cheek out here, we have the buccal or facial surfaces of the molars, and then the tongue is in here, and then we have the lingual surfaces of the molars. By the way, this is identical to the other diagram that we saw earlier in some of the

[03:40] videos we did in this series. You may recall from those videos the functioning cusps are the ones that should be in contact with the opposing tooth and for that reason they are appropriately centered over the opposing tooth. The non-functioning cusps on a

[04:00] other hand, tend to be taller, sharper, and their job is not to contact the oppositing tooth, but rather to hold the soft tissue, the cheeks and the tongue, away from the biting surfaces so you don't constantly bite them. That's exactly

[04:20] By the way, why people with posterior crossbite tend to bite their cheeks and have annoying traumatic ulcers all the time. Now I also want you to always remember a simple rule we're going to call the bull run.

[04:40] rule. That stands for buckle, upper, lingual, lower. These are the cusps that should not be in contact. If either of those cusps are involved in the occlusion, that's when you're much more likely

[05:00] to see abfraction, recession, TMD, cheek biting, all sorts of problems when we have these cusp interferences. These are non-functioning cusps for a reason and they should not be involved in the ideal typical occlusion.

[05:20] So, on the left in this slide is the same coronal plane image we were just looking at, but this time I highlighted in blue and magenta the two functioning cusp contacts. Over on the right hand side is now the axial plane image.

[05:40] This is a horizontal view looking at an upper quadrant of teeth and a lower quadrant of teeth. The reason why I'm showing these two images together is to show you the connection of these blue and magenta curves with these blue and magenta dots.

[06:00] Based on the curvature of the palatal root, this one looks like a maxillary first molar to me, so let's just say this tooth corresponds to this tooth of that diagram. This tooth will say then is a mandibular first molar corresponds to this tooth of that diagram.

[06:20] Imagine painting blue dots on all of these functioning facial cusps of the lower teeth, and painting magenta dots on all the lingual functioning cusps of these upper teeth. Now after drawing all of those dots, let's say

[06:40] We connect all those dots. We draw one big blue curve on all the functioning facial cusps and one big magenta curve on all of those functioning lingual cusps. Then you close the teeth together so that paint spreads to the opposing arch.

[07:00] After doing that, you're left with the curves that you see in this image. What we're going to call the blue curve is the facial range of occlusion and the magenta curve. We're going to call the lingual range of occlusion. Feel free.

[07:20] Also to pause the video here to let that really soak in. If you can really understand the connection between these two images and how the teeth come together in this way, you have a great starting point for understanding the next video in this series when we make things a

[07:40] little bit more complex and talk about how the teeth move in function when we're talking about pertrusive and lateral movements. And lastly is the sagittal plane or the front to back sagittarius firing a bone arrow view. This is arguably the

[08:00] most important to memorize for the board exam. So definitely pay attention to this part. This is a great diagram showing you how the teeth fit together, like puzzle pieces or the spokes on a gear, but it has limitations. Primarily, it's not for the board.

[08:20] feasible to reproduce this diagram on a piece of scrap paper when it's time for you to take your test. So, I'm going to show you the famous picket fence diagram, which has been around longer than I have, and it's one of my all-time favorite memory tools. And you can follow along with me on

[08:40] your own piece of paper. So first, you're going to want to draw nine vertical lines, and they can be evenly spaced out from one another. I like to make the first four a little bit farther apart, and then the next five a little bit closer together. So we have one, two, three.

[09:00] four, five, six, seven, eight, and then nine. After this step, we're going to make some zigzag peaks and valleys, so to speak. So what we'll do first is draw one, two zigzags. We'll draw another two zigzags.

[09:20] and then another two zigzags. At this point we're going to switch to just one zigzag for all the next lines. Alright so then we have completed one half of the diagram.

[09:40] All we have to do now is add in the lower lines and then label the diagram. So what we'll do for the bottom half is we're not going to start from back here. We're going to start from the first valley, the first downward-pointing zigzag we'll call it. And so let's draw one line from there.

[10:00] We're going to skip one zigzag and then draw another line down. We're going to skip another zigzag. And although it's tempting to want to draw the line right on that line, this is the one that's going to be a little bit weird. We're going to back up about halfway up this zigzag and draw it here instead.

[10:20] Then we're going to return to our normal pattern. So we'll skip one zigzag here, draw a line down, and then since we now have four lines, all the remaining ones are going to be just one zigzag away. So we'll do one, one, one, one. And in this one, we don't have enough.

[10:40] pointed down zigzags to draw from, so we just make it flush with the upper line. That is your completed diagram. So now all we have to do is label it. What this diagram is showing you is a simplified version of the diagram up here. So each of these little segments of the fence represents one

[11:00] of these teeth. If we start from left to right, this is going to be your third molar, this is going to be your second molar, your first molar, your second premolar, your first premolar, and of course this is all for the macro.

[11:20] axillary arch. Here's your canine, your lateral incisor, and then your central incisor, which I'm just calling I2 and I1. And then here is the mandibular arch. So hopefully your diagram looks something

[11:40] like that. So now if someone asked you on the exam what contacts the central fossa of the mandibular first molar, we can easily figure it out. First, thanks to the bull rule, we know which cusps should not contact.

[12:00] So by process of elimination, we know which cusps do contact. We know that it's the lingual cusps of the upper teeth and the buccal or facial cusps of the lower teeth that should be in contact with one another. So again, our question is what contacts

[12:20] the central fossa of the mandibular first molar. So here's the mandibular first molar. This is the distal cusp, the distofacial cusp, and the mesiofacial cusp of the mandibular first molar. And from our mandibular first molar video, we know the central fossa is located between the

[12:40] two cusps. Okay, so what part of the picket fence is contacting that point? It's going to be the mesiolingual cusp of the maxillary first molar. And that's your answer. We're done. We got it.

[13:00] So let's do another one. If someone asked what contacts the distal marginal ridge of the mandibular first premolar, we just have to find mandibular first premolar. Here's the distal marginal ridge. Okay, so it has to be the lingual cusp of the

[13:20] maxillary first premolar. And that's it. How about the distal marginal ridge of the maxillary lateral incisor? Here's the maxillary lateral, here's the distal marginal ridge. Oh, it's gonna be the cusp tip of the mandibular canine. There you go. That's it. So that's as easy

[13:40] as we can possibly make it thanks to this diagram. And so if you can reproduce this on your scrap paper, you're going to be in great shape. Now, the other thing that I want to point out, this diagram also reveals two very good high-yield facts to remember for the board exam, separate from...

[14:00] these kind of questions I'm asking you right now. So in an ideal class 1 occlusion, which is what this is showing, the maxillary canine, this tooth right here, is the only tooth that contacts both an anterior and

[14:20] a posterior antagonist. So these are all the anterior teeth and then these are all the posterior teeth, premolars and molars. And so the maxillary canine, not the mandibular canine, the maxillary canine is the only tooth that contacts both an anterior tooth and a posterior tooth.

[14:40] in an ideal class 1 occlusion. And the second high yield fact is that all teeth occlude with two other teeth. So this tooth contacts this tooth and this tooth, this tooth contacts this tooth and this tooth, this tooth contacts this tooth and this tooth, except

[15:00] for the mandibular central incisor and the maxillary third molar. Both of these teeth only contact one other tooth. All right, so with all of that said, I would love for you to give these examples a try.

[15:20] Keep in mind, now I'm adding in specific tooth numbers, so take your time identifying where on the picket fence that tooth number would appear. And just so you know, DMR stands for distal marginal ridge, MMR is mesial marginal ridge, and DF is distal

[15:40] facial, mesialingual, and distalingual. So pause the video, give these a try, and then resume the video once you're ready to check your answers. Alright, so three, two, one, here are all the answers. And notice that all of the numbers in

[16:00] each row, 20 and 13, 19 and 14, 3 and 30, add up to 33. And so that's a pretty cool, fun fact here. And it's not a coincidence because nine times out of 10, these two

[16:20] numbers will in fact add up to 33. Otherwise it will add up to either 32 or 34, depending on where you are in the arch. And so that's just a nice little thing to double check yourself. Most of the time it will be 33, or it could sometimes be 32 or 34.

[16:40] for, but it will never, unless you're of course not in a class 1 occlusion, it will never add up to something that's not one of those numbers. Alright, so that's it for this video everyone. I hope you enjoyed it. I love doing it. This is a cool topic and we'll see you next time when we talk about working.

[17:00] movement, and we make things a little bit more complex. So make sure you understand these foundational principles first before going on to the next video. That's it for this video. Thank you so much for watching. Please like this video if you enjoyed it, and subscribe to this channel for much more on dentistry.

[17:20] If you'd like to support me, please check out my Patreon page. And thank you to all of my patrons for their support. You can unlock access to my video slides to take notes on and practice questions for the board exams, so go check that out, the link is in the description. Thanks again for watching everyone, I'll see you in the next video.

[17:40] Bye!