Parts of the digestive system
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Voiceover: So now that we've talked about the mouth in general, let's put a smile on that face and take a look at the teeth in a little more depth. What we have here is an image of the lower jaw. Another term for the lower jaw is the mandible. This is your mandible right here and then this is your left side of the mandible so I'll put left, and this is your right side so you can follow along as we talk about your teeth. As you can notice here, things are pretty symmetric, right? I can draw a dividing line right down the center and as we go through and talk about every little tooth that we have, we'll see that we have the same tooth not just on the other side but also in your upper jaw, also known as the maxilla. This tooth right here? We have a mirror image of it here, and for this pair that we have, there's two of them in your upper jaw. Keep that in mind when we're going through and doing the math at the end. Every tooth has a specific function to it, or every set of teeth. Let's go through the different types of teeth we have. This first one we have is called the central incisor. The central incisor. Again, we have four central incisors in total. We have the one I've pointed out here, the second one here, and then two others in your upper jaw. The central incisor is mainly used for cutting. This is the tooth that you use to cut your food. The way you remember that is the reason why we call these incisors, just like in surgery we say we're about to make an incision, is we're about to make a cut. So the central incisors make incisions. The same thing is true when we talk about the lateral incisors. We've got four of them in total, just like the central incisors. There's only one on this side so I'll write 4 in total here. Again, they're also used for cutting our food. Now that we're done talking about our incisors, let's move on to talk about our canines. This is our canine tooth and we've got 4 of them in total. The canine tooth, they're also known as fangs and you'll see why and I'll show you in another image. They're the sharpest, longest teeth that we have and they're actually used for gripping. They're for gripping. You can imagine when you're going to a restaurant and they give you a bread basket at the beginning. You put a piece of bread in your mouth and you kind of pull away at it and you tear it apart because your teeth, the canine teeth that you have, all 4 of them are gripping on the bread that's in your mouth as your hand pulls the rest of it away. So I'll put 'pulling' in here just as a little cue as well for how we use our canines. Now that we're done with our canines, we can talk next about our premolars. So the premolars, we have two on each side, which means that in total, we have 8 of them. We have 8 premolars and the way to think about what these guys do is in two parts. One, if you see the word 'mola' over here, that's a reference to the Latin word 'mola' which just means to grind, or it actually represents grindstone. If you ever look at what a millstone is or a grindstone, those are called 'mola' in Latin and that makes sense because our premolar teeth are used for grinding down our food as we chew it. The other thing to keep in mind is this first part of the word, 'pre.' We call is 'pre' because these two premolar teeth come before these final three molar teeth. So we have three molar teeth right here, which means that we have a grand total of, you guessed it, 12 teeth. Just like the premolars, these guys are here for grinding as well, to break down our food as we chew on it for the same Latin root we discussed above. At this point, now that we've talked about all the different types of teeth, the interesting thing is that this textbook picture of what your lower jaw should look like is actually what it looks like in only 28% of people in the population. Why is that? I've got a nice panoramic image here. You might recognize somebody familiar whose image was taken here and it's nicely situated. This is your right side and this is your left side. This is actually a panoramic X-ray of me looking right at you. This is the front of my, as you now know them, the central incisors and these are the central incisors on my mandible down here. For reference, this top bone that holds your upper jaw is also known as the maxilla. So why don't we clarify that? This is my maxilla up here, and as you guys already know, this is my mandible. So I'll write mandible right here. What's interesting is when you look at the teeth that I have here, they're a little different from the image we saw previously. It's because if you count them, here's my central incisor, this is my lateral incisor, the canine, this is my first premolar, this is my second premolar, that's my first molar and this is my second molar. There's something missing here, and it's not just here, but it's actually missing on this side, this side and this side. I think you guessed it. All four of my third molars are gone. The reason why is because they were my wisdom teeth. Your third molars are called your wisdom teeth. Often people get these removed. In fact, 72% of people get these removed. 72% of our population removed the wisdom teeth. There's actually a pretty simple explanation for why that occurs. If you take a look at the gums that I have right here, so I'm just going to draw a rough drawing of my gums, and I'll try to make sure I exclude my teeth as I do this little tracing right here, but if you look at the gums that are surrounding every tooth I have in my mandible or my lower jaw right here, they have just enough space for every tooth to erupt or come out. Let me color that in. The way the tooth comes out is that there's a small designated hole. Let me draw one here for my second molar or if I want to draw one in over here for my lateral incisor, so that's the hole the lateral incisor erupted or emerged out of. The hole for the third molar sometimes ends up being pretty small. In fact, in 72% of people, it ends up being pretty small. The problem is that when my third molar is here, let me just draw this third molar in, and it wants to grow, naturally what you would want to see happen is for the third molar to go this way and then out and erupt through that hole. Unfortunately, this isn't what happens in most people. Instead, the third molar commonly tries to erupt through your gum or through your gingiva, which is an important term. I'll write that down. Your gums are also known as your gingiva. If they try and erupt through your gingiva, you can have things like inflammation or tearing of the gum or gingiva, or even an infection that occurs if it happens for an extended period of time. This commonly occurs in people within the age group of about 17 to 25 years old. That's why we call them wisdom teeth. By the time you gain a little bit of wisdom, you start having all four of your third molars erupt right through your gingiva. You want to get them removed before you can have some type of bad reaction like inflammation or infection that can occur that can mess up the neighboring teeth that have erupted or grew out so well. That's pretty cool if you can recognize that because the same X-ray that my dentist used to see that my wisdom teeth were removed correctly and safely, is something that you can now read and interpret by yourself.