Development of Teeth

00:01 Welcome to our discussion on development of the teeth.

00:04 Now, the most important thing to know about the teeth is that believe it or not, they are actually derivatives of the skin.

00:10 They are derived from the epidermis.

00:12 Now, teeth develop two times during our life.

00:15 The first time, we get our deciduous set which we can see here in this image within the mouth, and then, we have the adult set which develop during early childhood that grow until they´re able to erupt later on in our early childhood.

00:30 Now, the deciduous set of teeth consist of two incisor teeth, one canine, and two molars and it will be replaced by more teeth as our jaw enlarges.

00:40 We have two incisors, one canine, two premolars, and three molar teeth.

00:46 Now, that third wisdom tooth is sometimes present, sometimes is not able to fit into the space that´s allotted and we have to have it removed.

00:55 So many people only have two molars but initially, three are set to develop.

01:00 Now, early on, inside the mouth we have a lining of ectoderm and that ectoderm is going to develop thickenings and that thickening covers the entire roof of the mouth in a little bit of a C-shaped arch and on the floor of the mouth around the mandible in another C-shaped arch.

01:18 That is called the dental lamina and it´s going to thicken and move into the underlying mesoderm.

01:24 So initially, teeth for the exact same way that hair cells do.

01:29 They´re gonna invaginate into the underlying mesoderm and set up shop there and produce a new structure that grows outward but that´s about where the similarity ends.

01:40 The tooth buds migrate down into the underlying mesoderm and unlike hair, they will eventually detach from the surface and create the teeth entirely within the jaw or the maxilla.

01:52 So as the tooth bud moves into the underlying mesoderm, it remains connected to the surface by a dental lamina and as the tooth bud moves further and further in, it develops a bell shaped kind of appearance, a bell shaped structure and it then becomes called the enamel organ.

02:08 So the enamel organ as its name suggests will produce enamel, the toughest and most resilient mineralized structure in the human body.

02:16 So this bell shaped structure develops two lamina, an outer enamel epithelium and an inner enamel epithelium.

02:24 I want you to note that they´re called the enamel epithelia but they are not yet actual mineralized enamel.

02:31 They´re just gonna help create it.

02:33 So in between these two lamina, we have a collection of mesenchyme, loose, undifferentiated tissue called the stellate reticulum that´s gonna keep the two separate.

02:43 Now, as development proceeds, we´re going to have the bud of the permanent tooth, the one that develops later on in childhood and will eventually erupt and displace the deciduous tooth grow off of the dental lamina.

02:56 So we see its primordia right there.

02:59 After that permanent tooth buds off of it, the dental lamina is going to rescind, degenerate, and leave the enamel organ completely free from the outside epithelium.

03:09 So here we can see what´s left.

03:12 The bud of the permanent tooth is migrating more inferiorly.

03:16 The dental organ is completely within the mesenchyme of the mandible or the maxilla and at this point, the inner surface, the inside of that bell shaped structure is going to produce cells called ameloblasts.

03:30 So these ameloblasts are going to lay down the actual enamel, create the mineralized structure that covers the teeth and underneath them, we have another set of cells lining the papilla of the tooth called odontoblasts.

03:46 They´re gonna produce yet another mineralized structure called dentin.

03:50 Now, dentin is pretty tough, not as touch as enamel, but it´s gonna form the majority of the tooth whereas enamel only really covers the outside surface that has to handle all the chewing and other things that we ask teeth to put up with.

04:05 So the dental pulp at the core of each tooth has a lot of blood vessels, as well as a surprising amount of innervation.

04:12 Because our teeth are actually acutely sensitive not only to pain but pressure.

04:17 And the nerves and vessels in the papilla are what allow the tooth to do its good work of chewing but not fracturing or applying too much force every time we bite down.

04:27 The alveolar bone of the mandible or the maxilla starts developing around the enamel organ as the ameloblasts are creating more and more enamel and the odontoblasts are gonna be creating more and more dentin.

04:42 And you´ll notice as we proceed, the tooth keeps getting closer and closer to the surface whereas the permanent tooth, its little enamel organ keeps migrating further and further in so that when it erupts, it will actually displace the other deciduous tooth.

04:57 So here, we can see the tip of the tooth covered by enamel, about to rupture through the gum.

05:04 We still have odontoblasts creating dentin and an extended dental papilla right there.

05:11 The deciduous tooth is about to erupt and the permanent tooth is starting to develop underneath it.

05:17 And within four or five, six years, that deciduous tooth will actually be pushed out of its socket by the developing permanent tooth.

05:25 So when a tooth is actually erupted and present in the mouth, we have what´s called the anatomic crown.

05:31 That´s the portion that´s covered by enamel.

05:34 Just under that, we have the root, the portion that´s not covered by enamel and it´s going to be in conjunction with the bone of the mandible and the maxilla.

05:44 It´s gonna be held there but if we only had that tooth stuck in bone, it would be very rigid and teeth need to be able to wiggle.

05:52 One way that that´s done is that we have another mineralized tissue called cementum that helps keep it anchored inside the socket.

06:00 And there´s also gonna be some connective tissue developing in there as development proceeds as well.

06:07 That´s gonna be called the periodontal ligament.

06:10 And the periodontal ligament and cementum will let the tooth have a little bit of movement so that it´s not rigidly held.

06:16 Because rigid things tend to fracture and you do not want your tooth to fracture if you can help it.

06:21 When it comes to tooth development, anything that can go wrong will go wrong and on here we have what´s called an extra tooth due to an extra dental lamina moving into the jaw and we have an extra incisor tooth for this person.

06:35 On the opposite side, we can have two few dental lamina move into the maxilla or the jaw and that will result in tooth agenesis.

06:43 No teeth where there ought to be.

06:46 Sometimes, we´re gonna have two enamel organs develop off a single bud causing gemination of the tooth.

06:51 Here, we have two crowns tied to a single root and one thing about tooth development that you want to keep in mind is that exposure to tetracycline during the development will actually stain developing teeth yellow or brown and the color gets darker, the more tetracycline the person is exposed to as their teeth are developing.

07:11 Another thing that can happen is hypodontia, when a tooth is smaller than usual.

07:17 This is usually tied to sparse hair on the body and what´s interesting about that is hair and teeth develop in a very similar way.

07:25 The ectoderm moves into the mesoderm and then, creates the hair follicle or the tooth, so there´s a commonality between these two occurrences.

07:35 Macrodontia or teeth that are too large are really uncommon.

07:40 When this happens, it´s usually a part of another syndrome and you´re gonna wanna look for additional problems that may be present in anyone who presents with macrodontia.

07:50 As opposed to macrodontia, you can have fusion of teeth if their dental lamina are too close together.

07:56 As they develop, they can fuse and move out into the gum together.

08:00 Now, with roots, you can have roots that are too short and are poorly anchored into the jaw or the maxilla.

08:07 You can have extra roots or bifid roots where you´d expect to see only one.

08:12 These are not gonna be problematic unless you´re working to extract the teeth and have to account for their presence.

08:17 Now, when it comes to the process of laying down mineralized tissue, there are many steps involved and if there´s a problem or an enzyme deficiency in any of these steps, you can have amelogenesis imperfecta and that´s where enamel doesn´t form properly or doesn´t form at all.

08:35 Enamel is on the outer surface of our teeth for a good reason.

08:38 It´s the toughest most resilient structure we have.

08:41 So it helps us chew without having our teeth break.

08:45 So these teeth are going to tend to erode and be a little bit smaller than usual and more prone to decay.

08:51 On the opposite side, you can have dentin not form properly as well.

08:56 Dentinogenesis imperfecta is going to occur when the odontoblasts do not produce effective dentin and one really interesting hallmark of this is that sometimes imperfectly formed dentin is translucent and that´s what you can see in this picture.

09:11 The teeth are actually see through because the dentin has not been laid down properly.

09:16 Alright, thank you very much for your attention, and I´ll see you in our next talk.