WEBVTT 1 00:00:00.080 --> 00:00:02.160 You know, usually when you look at a piece of machinery, 2 00:00:02.359 --> 00:00:05.400 the engineering is like pretty obvious. You look at a hinge, 3 00:00:05.679 --> 00:00:07.120 you can see how it opens, right. 4 00:00:07.160 --> 00:00:09.000 You look at a shock absorber and there's a big 5 00:00:09.039 --> 00:00:10.560 spring right there exactly. 6 00:00:11.240 --> 00:00:13.839 But then you look at the human mouth and suddenly 7 00:00:13.919 --> 00:00:18.359 you're looking at this wild machine that has to crush 8 00:00:18.440 --> 00:00:22.000 rocks but also sense like a hair's width of. 9 00:00:21.960 --> 00:00:26.160 Pressure and survive a literal acid bath every single day. 10 00:00:26.399 --> 00:00:29.079 Yeah, and heal itself from the inside out. So today 11 00:00:29.160 --> 00:00:32.280 we're taking a deep dive into the dentin nbde Part 12 00:00:32.320 --> 00:00:35.359 one study guide. Our mission here is to help you 13 00:00:35.439 --> 00:00:38.079 master the foundational science of dentistry. 14 00:00:38.280 --> 00:00:41.159 Right. We're going to break down exactly how this biological 15 00:00:41.240 --> 00:00:44.240 marvel in your head actually works, from the macro anatomy 16 00:00:44.240 --> 00:00:46.520 of the jaw down to the microscopic cells. 17 00:00:46.719 --> 00:00:49.679 We're distilling everything down for you, whether you're a dental student, 18 00:00:50.119 --> 00:00:53.320 a young professional, or just you know, a curious self learner. 19 00:00:53.439 --> 00:00:55.640 So let's start big. If we open the mouth, we 20 00:00:55.679 --> 00:00:57.399 see the soft palette in the back. 21 00:00:57.320 --> 00:01:00.079 Which separates the oral cavity from the NASA fair. 22 00:01:00.520 --> 00:01:03.320 Yeah, right, But the real star of the show is 23 00:01:03.359 --> 00:01:06.040 the tongue. I mean, it looks like just a simple 24 00:01:06.079 --> 00:01:09.319 slab of muscle, but it is wildly complex. 25 00:01:09.439 --> 00:01:13.519 Oh, it's a massive bundle of intertwining fibers. And if 26 00:01:13.519 --> 00:01:16.079 you're trying to understand how this whole system is wired, 27 00:01:16.560 --> 00:01:19.920 the innervation of the tongue is a huge foundational concept. 28 00:01:20.159 --> 00:01:22.000 Okay, so what's the golden rule there? 29 00:01:22.079 --> 00:01:24.400 So the rule is that all the muscles of the tongue, 30 00:01:24.959 --> 00:01:27.519 the intrinsic ones that curl it and the extrinsic ones 31 00:01:27.519 --> 00:01:31.159 that move it around, they're all powered by one cranial nerve, right, 32 00:01:31.280 --> 00:01:33.439 the hypoglossal nerve. That's cranial nerve twelve. 33 00:01:33.439 --> 00:01:37.760 Okay, cranial nerve twelve. But I mean anatomy loves a curveball, right, 34 00:01:37.760 --> 00:01:39.840 There's always that one rogue element. 35 00:01:39.599 --> 00:01:43.959 Always, And here the notorious exception is the palatal glossus muscle. 36 00:01:44.120 --> 00:01:46.760 Even though it has glossus in the name, which. 37 00:01:46.560 --> 00:01:49.400 Means tongue exactly, it has glosses in the name, but 38 00:01:49.480 --> 00:01:53.239 it is actually innervated by the vagus nerve cranial nerve x. 39 00:01:53.560 --> 00:01:55.159 Oh wow, why is that? 40 00:01:55.280 --> 00:01:57.799 Because it pulls the soft palette down and elevates the 41 00:01:57.840 --> 00:02:00.359 back of the tongue to start a swallow. So since 42 00:02:00.400 --> 00:02:02.359 it bridges the throat and the tongue, it takes its 43 00:02:02.359 --> 00:02:03.680 wiring from the third snerve. 44 00:02:03.959 --> 00:02:06.040 That makes total sense. Now looking at the surface of 45 00:02:06.079 --> 00:02:10.000 the tongue, it's covered in these textural bumps, the lingual pipilla. 46 00:02:10.159 --> 00:02:12.840 Yeah, where your taste buds live. And they are definitely 47 00:02:12.879 --> 00:02:13.680 not all the same. 48 00:02:13.919 --> 00:02:15.759 Right, they have specific zones, don't they. 49 00:02:15.840 --> 00:02:18.360 They do so. At the very tip and along the 50 00:02:18.400 --> 00:02:22.360 sides you have the funderform pipillae. They look like well, 51 00:02:22.479 --> 00:02:24.840 little mushrooms, and they handle sweet and salty. 52 00:02:25.000 --> 00:02:27.000 Okay, sweet and salty on the mushroom yep. 53 00:02:27.479 --> 00:02:31.000 Then on the far lateral edges you have the foliot pipillae. 54 00:02:31.400 --> 00:02:35.560 Those look like leaflike folds and they pick up sour tastes. 55 00:02:36.039 --> 00:02:38.240 And then there's the bitter ones. At the back right. 56 00:02:38.120 --> 00:02:40.479 Right, drawing a big V shape at the back of 57 00:02:40.520 --> 00:02:44.000 the tongue are the circumvallet pipilla. These are huge circular 58 00:02:44.039 --> 00:02:46.520 structures and they sit in these deep trenches. 59 00:02:46.719 --> 00:02:50.400 Well, wait, if there are deep trenches, wouldn't like food 60 00:02:50.479 --> 00:02:52.479 just get stuffed down there? You'd be tasting that bitter 61 00:02:52.520 --> 00:02:54.240 coffee for hours, you'd. 62 00:02:54.039 --> 00:02:57.000 Think so, But nature solve that with von Ebner's glands. 63 00:02:57.159 --> 00:02:58.080 Okay, what are those? 64 00:02:58.159 --> 00:03:01.199 They are these purely serious salav glands right at the 65 00:03:01.199 --> 00:03:04.360 base of the trenches. Their only job is to constantly 66 00:03:04.479 --> 00:03:07.120 pump out watery fluid to wash the trench. 67 00:03:06.800 --> 00:03:09.000 Out like a biological reset button. 68 00:03:09.080 --> 00:03:11.680 Exactly, they flush the palette so you can analyze the 69 00:03:11.800 --> 00:03:13.960 chemical makeup of your very next bite. 70 00:03:14.000 --> 00:03:18.080 That is just brilliant engineering. But okay, tasting the food 71 00:03:18.120 --> 00:03:20.479 is only step one. Let's talk about the heavy lifters 72 00:03:20.479 --> 00:03:23.319 that actually crush it. The muscles of mastication. 73 00:03:23.639 --> 00:03:26.120 So there are four primary ones, and just like the tongue, 74 00:03:26.360 --> 00:03:29.560 these four are all wired to the same power source, 75 00:03:30.360 --> 00:03:34.159 the mandibular division of the trigeminal nerve V three. They 76 00:03:34.319 --> 00:03:36.800 also all get their blood from the maxillary artery. 77 00:03:37.159 --> 00:03:39.319 Okay, let's meet the big four. Give me the breakdown. 78 00:03:39.560 --> 00:03:43.199 First up is the temporalis. It's this massive fan shaped 79 00:03:43.319 --> 00:03:46.080 muscle on the side of your skull. Because of how 80 00:03:46.080 --> 00:03:48.879 it fans out, it elevates the jaw, but it also 81 00:03:49.080 --> 00:03:50.680 retracts it pulls it backward. 82 00:03:50.759 --> 00:03:51.680 Got it. What's number two? 83 00:03:51.879 --> 00:03:54.840 The massiter sitting right at the angle of your jaw. 84 00:03:55.319 --> 00:03:59.439 This is your powerhouse. The most powerful elevator of the mandible. 85 00:03:59.439 --> 00:04:00.840 I mean you can feel that one flecks when you 86 00:04:00.879 --> 00:04:01.400 clench your teeth. 87 00:04:01.479 --> 00:04:04.680 Oh. Absolutely. Then third is the medial terrygoid. It runs 88 00:04:04.680 --> 00:04:06.919 on the inside of the jaw. It basically forms a 89 00:04:06.960 --> 00:04:09.400 sling with the master to pull the jaw up and 90 00:04:09.439 --> 00:04:10.639 slightly side to side. 91 00:04:10.800 --> 00:04:14.360 Now, hold on a second. You just listed temporalis, massiter, 92 00:04:14.759 --> 00:04:17.639 and medial terrygoid. All three of those pull the jaw 93 00:04:17.680 --> 00:04:20.000 up right, they close the mouth. So how does it open? 94 00:04:20.240 --> 00:04:22.079 Like gravity can't do it all on its own. 95 00:04:22.199 --> 00:04:26.160 Well, the fourth muscle does the opening, the lateral terrygoid. 96 00:04:25.800 --> 00:04:27.720 So it's like the lone rebel of the group. 97 00:04:27.959 --> 00:04:30.160 That is the perfect way to describe it. It's the 98 00:04:30.199 --> 00:04:35.160 only one that depresses or opens the mandible. It also 99 00:04:35.199 --> 00:04:37.639 protrudes it dragging the jaw forward. 100 00:04:37.800 --> 00:04:39.839 And because it's the only one doing that job, it's 101 00:04:39.839 --> 00:04:40.959 a big clinical clue. 102 00:04:41.040 --> 00:04:44.800 Is a huge clue. If the lateral terarygoid is injured 103 00:04:44.839 --> 00:04:47.399 on one side, when you ask the patient to open 104 00:04:47.439 --> 00:04:51.040 their mouth, the jaw will physically deviate toward the side 105 00:04:51.040 --> 00:04:52.040 of the injury. 106 00:04:51.920 --> 00:04:54.800 Because the healthy side is pushing forward, but the broken 107 00:04:54.839 --> 00:04:57.040 side is just dragging behind exactly. 108 00:04:57.120 --> 00:05:01.079 It essentially anchors the jaw toward the broken side. Simple mechanics, 109 00:05:01.160 --> 00:05:03.439 but incredibly useful for diagnostics. 110 00:05:03.480 --> 00:05:05.959 Okay, so we've mapped the oral cavity, we have the crushers, 111 00:05:06.319 --> 00:05:09.160 but before we crush anything, we need the actual teeth 112 00:05:09.319 --> 00:05:11.879 we do, so let's shrink down to the microscopic level. 113 00:05:12.439 --> 00:05:14.839 You start as an embryo. How does a clump of 114 00:05:14.920 --> 00:05:16.759 cells figure out how to build a rock? 115 00:05:17.199 --> 00:05:20.360 It starts really early, around the sixth week in utero. 116 00:05:20.800 --> 00:05:22.879 You get this U shaped band of tissue in the 117 00:05:22.879 --> 00:05:24.839 developing mouth called the dental lamina. 118 00:05:25.040 --> 00:05:27.959 Okay, the dental lamina, and it's basically two tissues talking 119 00:05:27.959 --> 00:05:28.879 to each other, right right. 120 00:05:29.079 --> 00:05:33.800 It relies on chemical communication between the oral epithelium, which 121 00:05:33.839 --> 00:05:37.879 is ectoderm, and the underlying connective tissue, the ectome synchime. 122 00:05:38.399 --> 00:05:41.560 And when they talk, they form the tooth germ, which 123 00:05:41.600 --> 00:05:44.000 goes through the cap stage and then the bell stage. 124 00:05:44.120 --> 00:05:46.959 Yeah. And during the bell stage, this tooth germ splits 125 00:05:46.959 --> 00:05:51.639 into three highly specialized factories. First, you have the enamel. 126 00:05:51.399 --> 00:05:53.879 Organ, which comes from the ectoderm. Correct. 127 00:05:54.000 --> 00:05:57.079 It forms a literal bell shape, and it's made of 128 00:05:57.240 --> 00:05:59.120 four distinct cellular layers. 129 00:05:59.160 --> 00:06:01.079 Okay, what the four layers. That sounds like high yield 130 00:06:01.120 --> 00:06:02.800 exam stuff, very high yield. 131 00:06:02.879 --> 00:06:07.040 On the outside, you have the outer enamel, epithelium, protective 132 00:06:07.040 --> 00:06:08.040 barrier and blood supply. 133 00:06:08.160 --> 00:06:09.519 It makes sense. What's inside that. 134 00:06:09.639 --> 00:06:12.519 Inside that is the stellet reticulum. These cells are star 135 00:06:12.600 --> 00:06:15.759 shaped and they trap a ton of water. They act 136 00:06:15.839 --> 00:06:19.160 like a spongy shock absorber to protect the delicate stuff inside. 137 00:06:19.199 --> 00:06:21.199 Oh nice. And the third layer the. 138 00:06:21.120 --> 00:06:23.879 Stratum inner medium. It helps nourish the cells that will 139 00:06:23.920 --> 00:06:27.519 actually make the enamel. And finally, the innermost layer is 140 00:06:27.560 --> 00:06:29.480 the inner enamel epithelium. 141 00:06:29.639 --> 00:06:31.199 Those are the ones that actually do the building. 142 00:06:31.439 --> 00:06:35.480 Yes, those cells ultimately transform into ameloblasts, which are the 143 00:06:35.600 --> 00:06:36.920 enamel secreting cells. 144 00:06:37.040 --> 00:06:39.360 Okay, so that's the enamel factory. What about the rest 145 00:06:39.360 --> 00:06:39.879 of the tooth? 146 00:06:40.120 --> 00:06:42.839 Well, inside the bell of the enamel organ you have 147 00:06:43.120 --> 00:06:46.639 the dental papilla that comes from the ectomessen chyme and 148 00:06:46.720 --> 00:06:49.800 it forms the dentin and the pulp. Okay, and wrapping 149 00:06:49.839 --> 00:06:53.720 around the whole thing is the dental sac also ectomisenchyme. 150 00:06:54.079 --> 00:06:57.759 It forms the periodontium you know, the cementum, the periodontal ligament, 151 00:06:57.800 --> 00:06:58.519 and the bone. 152 00:06:58.600 --> 00:07:01.360 I always wondered about the timeline here. If enamel is 153 00:07:01.399 --> 00:07:04.319 on the outside and dentin is on the inside, which 154 00:07:04.360 --> 00:07:05.680 factory turns on first? 155 00:07:06.079 --> 00:07:10.079 It's an inductive relationship. One triggers the other. First, the 156 00:07:10.120 --> 00:07:14.199 cells of the inner enamel epithelium physically elongate. Okay, that 157 00:07:14.279 --> 00:07:18.079 shape change sends a chemical signal across to the dental papilla, 158 00:07:18.600 --> 00:07:22.360 telling its outer cells to turn into adentoblasts. 159 00:07:21.600 --> 00:07:23.319 The dentin making cells. 160 00:07:23.480 --> 00:07:27.720 Exactly, and those odontoblasts immediately lay down the very first 161 00:07:27.800 --> 00:07:29.360 microscopic layer of dentin. 162 00:07:29.600 --> 00:07:30.759 So the dentin goes first. 163 00:07:30.879 --> 00:07:33.399 Yes, and only after that first layer of denton is 164 00:07:33.399 --> 00:07:36.120 down do the ammeloblasts finally wake up and lay down 165 00:07:36.120 --> 00:07:37.160 the first layer of enamel. 166 00:07:37.279 --> 00:07:41.560 So dentin fires the starting pistol. The inside triggers the outside. 167 00:07:41.560 --> 00:07:44.959 That's so cool, and that brings us to the materials themselves, 168 00:07:45.040 --> 00:07:49.480 the big four enamel, dentin, cementum, and pulp. Let's start 169 00:07:49.480 --> 00:07:51.759 with enamel, the fortress. 170 00:07:51.319 --> 00:07:54.839 The fortress wall. It is the hardest, most mineralized substance 171 00:07:54.839 --> 00:07:57.639 in the human body. Ninety six percent in organic, ninety 172 00:07:57.680 --> 00:08:02.759 six percent yeah, almost entirely tightly packed. Hydroxyapoitatee crystals, zero 173 00:08:02.800 --> 00:08:07.000 collagen and mature. Enamel is completely acellular, no living cells 174 00:08:07.000 --> 00:08:07.680 at all, and. 175 00:08:07.560 --> 00:08:09.959 It's not just a flap block of crystal either. The 176 00:08:10.000 --> 00:08:13.439 sources talk about lines of Retzius and hunter Sriger bands. 177 00:08:13.279 --> 00:08:16.279 Right, because ameloblasts don't build in one continuous pore, they 178 00:08:16.360 --> 00:08:20.240 rest periodically. This creates visible growth rings like a tree. 179 00:08:20.519 --> 00:08:23.319 Those are the lines of Rhetzius and the hunter Strigger bands. 180 00:08:23.439 --> 00:08:28.160 That's an optical phenomenon. The ameloblasts weave the enamel rods 181 00:08:28.199 --> 00:08:31.079 in different directions to stop fractures. When you shine a 182 00:08:31.120 --> 00:08:33.720 light on it, those alternating directions look like light and 183 00:08:33.840 --> 00:08:34.559 dark bands. 184 00:08:34.759 --> 00:08:39.480 It adds incredible fracture resistance. But let me push back here. Sure, 185 00:08:39.600 --> 00:08:44.679 if enamel is ninety six percent crystal, completely dead, no 186 00:08:44.840 --> 00:08:48.320 nerves from up, how can my tooth feel pained when 187 00:08:48.360 --> 00:08:51.639 I drink ice water? A rock doesn't feel cold. 188 00:08:51.879 --> 00:08:54.960 It's a great question, and it's because enamel is just 189 00:08:55.080 --> 00:08:58.000 the shell right underneath that dead Cortreus is the dentin, 190 00:08:58.279 --> 00:08:59.919 and dentin is very much alive. 191 00:09:00.080 --> 00:09:03.559 So Denton is the sensory system and the shock absorber. 192 00:09:03.720 --> 00:09:07.320 Exactly, It's only about seventy percent inorganic. The rest is 193 00:09:07.320 --> 00:09:09.759 mostly organic material, primarily type. 194 00:09:09.519 --> 00:09:11.639 One collagen, which gives it flexibility. Right. 195 00:09:11.720 --> 00:09:14.440 It has a lower modulus of elasticity than enamel, so 196 00:09:14.480 --> 00:09:17.200 it can flex slightly and absorb the crushing forces without 197 00:09:17.200 --> 00:09:18.600 shattering the enamel on top of it. 198 00:09:18.840 --> 00:09:20.039 How is it alive. 199 00:09:20.120 --> 00:09:23.799 Because it's riddled with millions of tiny tunnels called dentinal tubules. 200 00:09:24.200 --> 00:09:26.480 Reaching up into every single tube is a living piece 201 00:09:26.519 --> 00:09:28.559 of a cell called a tomes fiber, which. 202 00:09:28.399 --> 00:09:30.240 Is an extension of the odonta blast. 203 00:09:30.399 --> 00:09:33.360 Yes, the main cell body sits in the pulp, but 204 00:09:33.440 --> 00:09:36.919 this long, fluid filled arm reaches up into the dentin. 205 00:09:37.679 --> 00:09:41.600 Changes in temperature or pressure shift the fluid, which tugs 206 00:09:41.600 --> 00:09:42.919 on the nerve endings. 207 00:09:42.559 --> 00:09:45.759 In the pulp, and that registers as pain exactly, And 208 00:09:45.840 --> 00:09:48.759 since it's alive, it can adapt, right, Yeah, I read 209 00:09:48.799 --> 00:09:50.279 there are four types of dentin. Yeah. 210 00:09:50.320 --> 00:09:54.039 Primary dentin forms the initial shape. Secondary dentin is formed 211 00:09:54.080 --> 00:09:55.759 slowly but continuously for. 212 00:09:55.759 --> 00:09:58.399 Your whole life, which means the pulp chamber gets smaller 213 00:09:58.440 --> 00:09:59.440 as we age. Right. 214 00:10:00.159 --> 00:10:02.120 If there's an attack like a deep cavity, you get 215 00:10:02.200 --> 00:10:06.720 tertiary or aperative dentin. The odonta blasts rapidly throw down 216 00:10:06.799 --> 00:10:10.039 this chaotic layer to physically wall off the decay like 217 00:10:10.200 --> 00:10:15.440 barricading the door exactly, and finally, sclerotic dentin. In older teeth, 218 00:10:15.519 --> 00:10:20.159 the tubules actually calcify and plug themselves solid to block bacteria. 219 00:10:20.480 --> 00:10:23.360 That is wild. Okay, moving down, we have cementum on 220 00:10:23.399 --> 00:10:24.799 the root and the pulp inside. 221 00:10:24.919 --> 00:10:28.639 Cementum is about fifty percent inorganic. Heavily resembles bone, but 222 00:10:28.679 --> 00:10:31.919 it's totally a vascular no blood vessels. Its only job 223 00:10:31.960 --> 00:10:32.919 is attachment. 224 00:10:32.600 --> 00:10:35.120 And the pulp is the vascular center, packed. 225 00:10:34.840 --> 00:10:39.440 With blood vessels, nerves, connective tissue. Its primary job is formative. 226 00:10:39.840 --> 00:10:41.679 It keeps those odonta blasts alive. 227 00:10:41.879 --> 00:10:44.639 Now, the study guide makes a huge clinical distinction about 228 00:10:44.639 --> 00:10:47.399 pulp capping, right, saving an exposed pulp. 229 00:10:47.559 --> 00:10:50.399 Yes, it's way more successful in young teeth than in 230 00:10:50.480 --> 00:10:51.399 older adults. 231 00:10:51.519 --> 00:10:53.240 Why is age such a big factor there? 232 00:10:53.360 --> 00:10:57.240 It's purely about blood supply. In young tooth, the opening 233 00:10:57.279 --> 00:10:59.200 at the tip of the root, the apical form in 234 00:10:59.399 --> 00:11:02.600 is wide open. The pulp is bursting with blood. 235 00:11:02.360 --> 00:11:04.559 Vessels, so it has a massive immune response. 236 00:11:04.639 --> 00:11:08.159 Right, it can fight inflammation and heal. But as we 237 00:11:08.240 --> 00:11:11.799 age that secondary dentin shrinks the canal the form and 238 00:11:11.960 --> 00:11:15.559 narrows and the pulp gets fibrous. It just lacks the 239 00:11:15.559 --> 00:11:17.200 blood supply to mount a defense. 240 00:11:17.360 --> 00:11:19.799 That makes perfect sense. Okay, so we've got this living 241 00:11:19.919 --> 00:11:22.360 sensing tooth. But if you just drop a tooth into 242 00:11:22.360 --> 00:11:24.519 a hole in the jawbone, it's not going to stay. 243 00:11:24.639 --> 00:11:26.440 It'd be like setting up a tent with no pegs. 244 00:11:26.679 --> 00:11:28.960 Right, first bite of an apple and the tooth is gone. 245 00:11:29.039 --> 00:11:30.120 So what are the tent pigs? 246 00:11:30.320 --> 00:11:34.840 That's the periodontium, specifically the periodontal ligament or PDL. It 247 00:11:34.919 --> 00:11:37.559 sits in a tiny space, usually less than point two 248 00:11:37.600 --> 00:11:41.159 millimeters between the root cementum and the alveolar bone. 249 00:11:41.240 --> 00:11:43.080 And it's not just passive glue, No. 250 00:11:43.200 --> 00:11:48.200 It's a highly cellular vascular Hammock type one collagen fibers. 251 00:11:48.600 --> 00:11:51.919 The terminal ends of these fibers embed directly into the hard. 252 00:11:51.759 --> 00:11:53.159 Tissue, the sharpiees fibers. 253 00:11:53.279 --> 00:11:56.879 Yes, they are calcified into the cementum on one side 254 00:11:56.919 --> 00:11:59.440 and the bone on the other. An incredibly resilient anchor. 255 00:12:00.480 --> 00:12:03.799 If the tooth is glued into solid bone with calcified ropes, 256 00:12:04.159 --> 00:12:06.960 how do braces work? Like? How do you drag a 257 00:12:07.080 --> 00:12:09.279 tooth an inch across the jaw? Without just ripping the 258 00:12:09.360 --> 00:12:09.759 root out. 259 00:12:09.919 --> 00:12:14.240 It relies on a fundamental biological discrepancy. Cementum is more 260 00:12:14.320 --> 00:12:17.039 resistant to being broken down than alveolar bone. 261 00:12:17.080 --> 00:12:19.120 Is okay, So how does that play out? When you 262 00:12:19.279 --> 00:12:20.000 tighten the wire. 263 00:12:20.279 --> 00:12:23.080 When you apply a continuous pressure, you compress the PDL. 264 00:12:23.200 --> 00:12:26.759 On one side, that's the pressure side, osteoclasts wake up 265 00:12:26.759 --> 00:12:28.919 there and start dissolving the jawbone to get out of 266 00:12:28.919 --> 00:12:31.320 the way. And on the other side, the tension side, 267 00:12:31.559 --> 00:12:34.559 osteoblasts wake up and lay down new bone to fill 268 00:12:34.600 --> 00:12:35.679 the gap behind the tooth. 269 00:12:35.960 --> 00:12:38.840 It's literally like dragging a hot wire through a block 270 00:12:38.879 --> 00:12:41.840 of ice. It melts ahead of the wire and freezes 271 00:12:41.919 --> 00:12:42.519 right behind it. 272 00:12:42.720 --> 00:12:46.000 That is a phenomenal visual and because the cementum is 273 00:12:46.080 --> 00:12:50.080 highly resistant to those osteoclasts, the root stays intact while 274 00:12:50.080 --> 00:12:51.879 the bone melts and reforms around it. 275 00:12:52.039 --> 00:12:55.279 Unbelievable and ceiling. The top of this system is the gingeeva, 276 00:12:55.559 --> 00:12:56.519 the gums. 277 00:12:56.279 --> 00:12:59.279 Right the biological seal. You have the free gin jieva 278 00:12:59.360 --> 00:13:03.879 forming a call and the attached gingeeva bound to the bone. 279 00:13:04.000 --> 00:13:07.360 But the critical barrier is the junctional epithelium. How does 280 00:13:07.399 --> 00:13:10.679 that attach the soft tissue physically glues itself to the 281 00:13:10.840 --> 00:13:16.000 enamel using microscopic hemidesmosomes and a basal lamina. It stops 282 00:13:16.159 --> 00:13:18.519 oral bacteria from diving down into the bone. 283 00:13:18.720 --> 00:13:22.240 Speaking of the teeth themselves, the sources highlight some specific 284 00:13:22.279 --> 00:13:24.440 clinical quirks that just ruin a dentist day. 285 00:13:24.519 --> 00:13:28.120 Oh. Absolutely. The classic trap is the maxillary first premolar. 286 00:13:28.480 --> 00:13:29.200 What's wrong with it? 287 00:13:29.200 --> 00:13:33.240 It features a severe mesual root concavity, basically a deep 288 00:13:33.440 --> 00:13:35.919 trench like groove on the side facing the front of 289 00:13:35.960 --> 00:13:40.600 the mouth. Biologically, plaque hides deep in there, huge periodontal 290 00:13:40.679 --> 00:13:42.840 risk and klindically if you have to do a filling there. 291 00:13:42.840 --> 00:13:45.039 Trying to adapt a flat metal matrix span into that 292 00:13:45.080 --> 00:13:47.360 deep depression is incredibly frustrating. 293 00:13:47.440 --> 00:13:49.039 I can imagine. What about the lower jaw. 294 00:13:49.200 --> 00:13:53.879 The mandipular first premolar is structurally fascinating. It's technically a 295 00:13:53.919 --> 00:13:57.840 bicuspit meaning two cusps, but its interlingual cusp is so 296 00:13:58.039 --> 00:14:01.480 tiny and non functioning. It way more like a canine 297 00:14:01.480 --> 00:14:02.240 than a pre molar. 298 00:14:02.320 --> 00:14:04.080 It tears food instead of crushing. 299 00:14:03.799 --> 00:14:07.960 It exactly and moving further back. The maxillary first molar 300 00:14:08.080 --> 00:14:12.320 is a giant, prominent oblique ridge crossing the surface, and 301 00:14:12.399 --> 00:14:15.039 it frequently has an extra little mini cusp on the 302 00:14:15.039 --> 00:14:17.519 inside front corner, called the cusp of carabelly. 303 00:14:17.919 --> 00:14:20.639 Good to know. Now, if you listening right now, run 304 00:14:20.679 --> 00:14:24.080 your tongue along your teeth, you'll notice they aren't flat squares. 305 00:14:24.399 --> 00:14:27.320 There are these triangular spaces between them called embrasures. 306 00:14:27.480 --> 00:14:27.720 Right. 307 00:14:28.000 --> 00:14:29.559 Why do we have those? Why not just have a 308 00:14:29.559 --> 00:14:32.039 perfect solid brick wall of teeth. 309 00:14:32.200 --> 00:14:34.720 If they were flat squares, every time you bit down 310 00:14:34.759 --> 00:14:37.159 on tough food, it would be driven straight down like 311 00:14:37.200 --> 00:14:40.519 a wedge, crushing the delicate gums between your teeth. 312 00:14:40.559 --> 00:14:43.399 So the embrasers act as like spillways. 313 00:14:42.879 --> 00:14:46.080 Yes, biological spillways. They direct the crushed food out to 314 00:14:46.120 --> 00:14:48.759 the sides, away from the gums, makes the teeth self 315 00:14:48.799 --> 00:14:51.799 cleansing and prevents frictional trauma. 316 00:14:51.240 --> 00:14:53.559 Which brings us to how the upper and lower arches 317 00:14:53.639 --> 00:14:59.639 meet cocclusion. The textraws a huge line between maximum intercuspation 318 00:15:00.159 --> 00:15:02.600 or MIICP and centric relation. 319 00:15:03.000 --> 00:15:06.840 Okay, so MIICP is purely tooth guided. It is just 320 00:15:06.919 --> 00:15:09.759 the position where your upper and lower teeth fit together 321 00:15:09.840 --> 00:15:12.120 the tightest you bite down the gears lock. 322 00:15:12.279 --> 00:15:14.320 That's MIICP and centric relation. 323 00:15:14.840 --> 00:15:17.879 Entirely joint guided has absolutely nothing to do with the teeth. 324 00:15:17.919 --> 00:15:21.120 It's the most superior stable position of the condyle in 325 00:15:21.159 --> 00:15:22.200 the TMJ socket. 326 00:15:22.320 --> 00:15:25.200 So a dentist's goal is usually to align the bite 327 00:15:25.240 --> 00:15:28.399 so your tightest tooth fit naturally happens when the joint 328 00:15:28.440 --> 00:15:31.399 is in that stable cr position exactly. The text also 329 00:15:31.440 --> 00:15:35.440 contrasts bilateral balanced decclusion with mutually protected occlusion. Right. 330 00:15:35.440 --> 00:15:38.159 A bilateral balanced declusion is for complete dentures. If a 331 00:15:38.240 --> 00:15:40.960 denture patient slides their jaw left, you actually need the 332 00:15:41.000 --> 00:15:43.039 teeth on the right side to stay in contact. 333 00:15:43.200 --> 00:15:44.840 Why wasn't that getting the way? 334 00:15:44.919 --> 00:15:47.279 If they separate, the denture tips up and falls out 335 00:15:47.279 --> 00:15:50.320 of the mouth, you need simultaneous contacts everywhere to keep 336 00:15:50.360 --> 00:15:51.679 the acrylic plate stable. 337 00:15:51.840 --> 00:15:54.360 Ah okay, but you absolutely do not want that in 338 00:15:54.399 --> 00:15:55.679 a mouth with natural roots. 339 00:15:55.879 --> 00:15:59.919 Correct for natural teeth, the gold standard is mutually protected occlusion, 340 00:16:00.639 --> 00:16:02.159 also called canine guidance. 341 00:16:02.200 --> 00:16:04.919 So if you slide your jaw to the side right now. 342 00:16:04.799 --> 00:16:08.120 You should feel your upper and lower canines touch and 343 00:16:08.159 --> 00:16:12.120 physically force all your back teeth apart. Canines have massive 344 00:16:12.200 --> 00:16:16.159 roots designed to absorb those sideways grinding forces. 345 00:16:15.879 --> 00:16:18.960 So they protect the back teeth during lateral movements, and 346 00:16:19.000 --> 00:16:21.559 the back teeth protect the front when chewing straight up 347 00:16:21.600 --> 00:16:21.919 and down. 348 00:16:22.039 --> 00:16:23.799 It's an incredibly elegant. 349 00:16:23.360 --> 00:16:26.799 System, but not invincible. Let's look at pathology. What takes 350 00:16:26.799 --> 00:16:27.679 this fortress down. 351 00:16:28.039 --> 00:16:31.679 The primary architect of smooth surface cavities is a bacteria 352 00:16:31.720 --> 00:16:33.240 called Streptococcus mutants. 353 00:16:33.440 --> 00:16:35.799 And it doesn't just eat the enamel directly, does it. 354 00:16:35.960 --> 00:16:38.559 No, it's basically throwing a chemical weapon at the wall. 355 00:16:39.360 --> 00:16:43.879 S Mutants consumes fermentable carbohydrates, mostly sugar, and it secretes 356 00:16:43.960 --> 00:16:44.960 lactic acid as. 357 00:16:44.840 --> 00:16:46.639 A byproduct, which drops the pH. 358 00:16:46.840 --> 00:16:50.679 Right. Enamel is strong but very vulnerable to acid. When 359 00:16:50.679 --> 00:16:53.919 the oral pH drops below five point five, the acid 360 00:16:54.000 --> 00:16:58.279 leaches calcium and phosphate out of the crystals, demineralization exactly. 361 00:16:58.279 --> 00:17:01.279 If it stays below five point five, the structure collapses 362 00:17:01.320 --> 00:17:02.720 and you get a cavity and. 363 00:17:02.720 --> 00:17:06.319 Decay in the mouth rarely stays isolated. Right. The guide 364 00:17:06.400 --> 00:17:09.599 emphasizes systemic links, especially diabetes melitis. 365 00:17:09.640 --> 00:17:13.400 The link is absolute. The classic triad of uncontrolled diabetes 366 00:17:13.440 --> 00:17:15.880 is polydipsia excessive. 367 00:17:15.400 --> 00:17:17.599 Thirst, polyphagia excessive. 368 00:17:17.200 --> 00:17:22.519 Hunger right and polyuria excessive urination. But the dental reality 369 00:17:22.559 --> 00:17:27.720 is severe. Diabetics lose twice as many teeth as non diabetics. 370 00:17:27.279 --> 00:17:30.519 Twice as many. Why is the bone laws so aggressive? 371 00:17:30.759 --> 00:17:34.519 It comes down to microvasculature. Chronic high blood sugar causes 372 00:17:34.599 --> 00:17:38.440 proteins in the blood vessels to glycate. This physically thickens 373 00:17:38.480 --> 00:17:40.400 the walls of the tiny capillaries feeding the. 374 00:17:40.440 --> 00:17:43.119 Gums, so it restricts blood flow severely. 375 00:17:43.400 --> 00:17:46.519 Oxygen and immune cells can't reach the periodontium to fight 376 00:17:46.559 --> 00:17:50.799 off normal plaque. The immune response becomes dysfunctional, inflammation runs rampant, 377 00:17:50.839 --> 00:17:53.039 and the alveolar bone is rapidly destroyed. 378 00:17:53.079 --> 00:17:56.319 Wow, and this vulnerability isn't just an adulthood. The text 379 00:17:56.319 --> 00:17:59.359 notes problems can begin in the first trimester of life with. 380 00:17:59.480 --> 00:18:03.599 Teratogea teratogens or external agents like drugs or viruses that 381 00:18:03.640 --> 00:18:07.160 disrupt fetal development. The first trimester is the critical window 382 00:18:07.200 --> 00:18:10.759 of organogenesis when the dental, lamina, and facial structures are forming. 383 00:18:11.000 --> 00:18:12.839 So what happens if there's exposure then. 384 00:18:13.680 --> 00:18:17.319 The consequences are permanent. For instance, if a pregnant mother 385 00:18:17.440 --> 00:18:21.799 takes the antibiotic tetracyclan, then the drug physically binds to 386 00:18:21.839 --> 00:18:24.240 the calcium in the forming tooth. 387 00:18:24.119 --> 00:18:28.480 Germ, resulting in that permanent dark intrinsic staining of the dendsins. 388 00:18:28.160 --> 00:18:31.839 Yes or exposure to the Rubella virus during that exact 389 00:18:31.880 --> 00:18:35.559 window can drastically alter the shape of the teeth and jaw. 390 00:18:35.759 --> 00:18:37.599 The timing dictates the defect. 391 00:18:37.799 --> 00:18:41.279 It is all profoundly connected from the first trimester right 392 00:18:41.319 --> 00:18:44.079 through to old age. We've covered an immense amount of 393 00:18:44.079 --> 00:18:47.680 ground today. We mapped the tongue's nerves, watched the lateral 394 00:18:47.759 --> 00:18:50.559 terigoid pull the jaw open, saw a dent and trigger 395 00:18:50.680 --> 00:18:51.400 enamel formation. 396 00:18:51.599 --> 00:18:53.240 We covered a lot of biology today. 397 00:18:53.279 --> 00:18:55.799 We did. We felt the living denin under the Dead 398 00:18:55.839 --> 00:18:59.960 Crystal Fortress, watched bone meld for orthodontics, and explored how 399 00:19:00.000 --> 00:19:02.079 I would drop in pH where a spike in blood 400 00:19:02.079 --> 00:19:03.480 sugar can tear it all down. 401 00:19:03.599 --> 00:19:06.559