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Running Time: 49 min

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Review dental classifications and terminology of teeth Discuss the appearance and function of teeth Review dental terminology on the anatomical landmarks of teeth Review the three most common teeth numbering systems Discuss odontogenesis including some common anomalies Review location and function of the hard and soft dental tissues Release: 9/26/2014 | Expires: 9/26/2017

Release Date: September 30, 2014

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Dental anatomy and tooth morphology is really important to us, hygienists, when we think of our instrumentation principles and really getting a good review of that evolution of the anatomy so that we can apply it in our clinical practice on a day-to-day basis. So I’d like to invite you on a journey today. Going over a few objectives here, I thought we would start out with just the dental classification and terminology of teeth, then moving on to what are the functions of the teeth. I think we are all aware of the very important functions that teeth provide. But also understanding the anatomical landmarks of the teeth and, of course, traveling worldwide, everyone has different systems of calling teeth in a different numbering way. So we’re going to review the taxonomy of teeth today and a little review on our embryology histology lectures from school and discuss odontogenesis today. And we’ll finish off the module with a good review on the hard and soft dental tissues of the anatomy today. So moving on, let’s look at the animal kingdom and the dental classifications we have within that. There are two types of teeth– the homodont and the heterodont. And homodont is the teeth that are actually uniform. They look the same, just like that picture shows of a beluga whale. There are also variations and classifications of the number and sets of teeth that we have. A polyphyodont has multiple or endless succession of teeth like the shark mandible picture that you see there. And hence, it’s probably a very feared mammal in our world. A monophyodont is something that just has one set of teeth. And of course, human beings are diphyodont. “Diphyodont” is a Greek word, actually, for two generations of teeth. It literally means that. And so that is a quick review of the classification system of the teeth. So looking at human beings who are heterodonts and diphyodonts. “Diphyodonts” mean, actually, two generations of teeth. And those are the primary and permanent dentitions. As you can see from this human skull, this is showing the two sets of teeth. The primary being removed by the permanent ones moving in right there. We also have further classification of the human dentition in which we have arches. We have the maxillae and the mandible. And each arch is further divided into two quadrants each. So the maxillae has two quadrants, the mandible has two quadrants, giving us four quadrants. We also have a numbering system for these quadrants. And we always start with the upper right area as quadrant number 1 and move in a clockwise direction to signify the numbering system, progressive numbering of the quadrants there. And numbering and taxonomy becomes important. And the terminology has to be uniform because we are communicating in different languages and different timings. So it becomes very necessary and important to define the terms in a common basic terminology. Let’s talk about terminology as it relates to the surface of the teeth, so we are all understanding of what surfaces we’re referencing. There are several terms to help us define these locations on the teeth. And some of the key ones that I’d like to highlight today, of course, mesial is anything that’s towards the midsagittal line. So anything that’s closest to the midsagittal line is referred to as mesial. Distal, of course, is the opposite of that, which is away from the midsagittal line. Buccal relates very much to the cheek side of the teeth. Sometimes, if it’s on the lip side of the teeth, of course, it’s called labial surface. Lingual refers to the tongue side of the teeth. So anything that’s facing towards the tongue is termed “lingual.” Palatal, of course, the same notation is for the palatal aspect of the teeth. Occlusal is the biting surface. Of course, the back teeth and incisal is relating more to the anterior teeth biting surface. So really, from all these surfaces, the five most common ones that I think we will make reference to and have to remember and they work in opposite directions, of course, is the buccal and lingual; mesial and distal; and then, of course, the occlusal or incisal, which is the biting surfaces. So those are probably the most five common universal surfaces that I’ll be making reference to. Let’s talk about the classes of teeth. As we know, we have 32 teeth in the permanent dentition, but only 20 teeth in the primary dentition. And really, that is to do with the number of classes of teeth we have. Permanent dentition has four classes of teeth– incisors, the canines, premolars, and molars. And we’re going to talk about the functions of each one of these teeth and their unique locations. But the primary dentition does not have any premolars in it. So really, it just equates to 20 teeth of just the incisors, the canines, and the molars. No premolars in the primary teeth. I think what’s unique about this module as I was preparing it and as I learn it and share it with the worldwide audiences is that no two teeth are alike. Every tooth has some unique feature to it. So let’s go on and explore the uniqueness of each classes of dentition. We also know that the permanent dentition in a patient’s mouth actually forms as early as 20 weeks of fetal development. And so, if you have a female patient in the chair who just found out she’s eight weeks pregnant, what an opportunity for us as hygienists to educate the patient that, did you know your baby’s first tooth is actually starting to form anywhere from six to eight weeks of prenatal life and your permanent tooth for the baby is going to start forming around the 20th week of fetal life? So excellent educational opportunity for us to refresh our memories on. And as we all know, the permanent tooth will erupt intraorally around the age of 6. And usually, by the age of 12, most of the teeth are out. The third molar was the exception of being more in the late teens and the 20s. And I’m finding more and more, it’s impacted or horizontal. It’s missing a lot of the times, I find in my patients. So moving on, then, just to summarize the human dentition and the classification, that we said that there are two sets and that there are the two arches and that there are four types of the teeth aside from the primary dentition, which has three. And then we talked about the four quadrants and the numbering system. So how can we now take the principles of dental anatomy and tooth morphology to actually apply to our instrumentation principles on a day-to-day basis? Let’s look at the actual function and the appearances of teeth, moving forward. We talked about the eight incisors that we have in the dentition. And their primary function, of course, is for cutting and shearing, unlike the canines, which are actually the cornerstones of your mouth. And their function is to tear food and really bring down the food particles to a chewing ability, which is then carried on by the premolars and molars, which actually crush and grind the teeth. So it’s fascinating that functions vary and yet the end objective is to help with the biting and chewing of the teeth. With the incisors, of course, the three major functions, aside from mastication, is the aesthetic value and to be able to speak and the phonetics of it all. So how they line up, the shape, the size of all these teeth become very critical in the look of the face. A lot of times, you’ll notice that a patient’s profile changes totally, especially if they have some front teeth that are missing. So really, the other important thing with the incisors is to notice that the mandibular incisors are actually the smallest teeth. And the lingual surfaces have no grooves at all. Now, this is clinically significant because a lot of times we will have subgingival calculus lodged on those areas there. And we’ll notice that it will come out in a big satisfying activation stroke. And the reason for that is the surface is fairly smooth and doesn’t retain the ledges of calculus too tenaciously, unlike some other surfaces on the teeth. Well, let’s talk about the other teeth. And talking of the canines, we had talked about them being the longest tooth. It’s actually got the longest root of the tooth in the mouth. And it is the “cornerstones” that I alluded to. It is a single cusp tooth. And as we mentioned, it tears food, but it also holds and pierces food. The unique thing about the canine is that it can withstand tremendous lateral pressure on chewing. And that becomes important as part of this function of mastication. Premolars are sandwiched between the canines and the molars, of course. And they have, at least, two cusps. And the buccal cusp is usually the one that’s the largest one. And again, their function is for chewing and grinding. And they usually erupt around age 10. So you’ll have the permanent molar erupting prior to the premolar erupting in the mouth. The molars, of course, are, again, fairly unique. They are the largest teeth in the mouth. And they don’t have any predecessors, so they actually erupt on an area where there was no teeth before. And the first molar, especially, is very well developed. The maxillary molar usually has four cusps, but it can have up to five cusps on teeth. The cusp of Carabelli, of course, in the maxillary first molar. And it has three very well-formed roots– two buccal and two lingual. What’s interesting about the mandibular molar is that the roots become less divergent as you go from anterior to posterior. And they’re, again, take on a large force on mastication. I think I read somewhere, it’s 250 pounds per square inch of force. And that’s probably on a good day, when you’re punching or grinding your teeth. So they’re amazing in their functionality and durability of what these teeth, molars, are capable of doing for us on a daily basis. Let’s review, then, the dental terminology. And then we’re going to go over the anatomical landmarks. This becomes very critical for us in our daily dental hygiene instrumentation tips that we use. So starting out with just describing the landmarks, we all know the crown is that visible part of the tooth, intraorally. And it’s the area that’s above the cementoenamel junction. And really, it’s covering and holding the most important organ as far as sensitivity goes. And that’s the pulp chamber which is preceded by the dentin. The root is the structure of the tooth that’s below the cementoenamel junction. We reviewed the five major surfaces of the teeth, being the buccal/facial and lingual, mesial and distal, and of course, the occlusal incisal surfaces. We’ve talked about the cusps being those prominence or eminence of the enamel. And it can vary from single cusp to up to four or five cusps, like we said in the molars. The cingulum is that convexity that’s located, actually, more on the lingual surfaces of your anterior teeth. And it’s usually around the gingival third area. And it’s unique to every person. Some people have a more convex cingulum than the other, and that has its manifestations or implications for calculus development as well. Ridges are just linear flat elevations. And they are named precisely based on location. So if it’s a mesial or lingual, they’re not showing the fusion of a mesial surface and a lingual surface or a ridge. Embrasures refer to the space that’s in between the two adjacent teeth. And of course, mamelons are the small developmental bumps actually. And I think I have a picture of that a little later on to show you. Usually present just on the incisal surface of primary dentition only. I made reference of convexity in the cingulum as to the gingival third. So just to refresh our memories, the crown is divided into three areas. We have the gingival third. That’s closest to the CEJ. And then we have the incisal or occlusal third. And the area in between signify the middle third. So this is describing the tooth in the three thirds, from an apical to an incisal edge. However, tooth can also be divided into thirds from a mesial-distal angle as well. So this would be signifying the mesial third. This is signifying the distal third. And then this is the middle third. So just a quick refresher on what the “third” meant. So the cingulum area that I referred to earlier on is a convexity on the lingual aspect of the maxillary incisors usually. And it’s in the gingival third area. How do we describe shapes of crowns of teeth? And usually, there’s three basic geometric shapes that we follow. Teeth are either triangular, trapezoidal, or rhomboidal in shape. And no matter which, whether it’s a molar or incisor, they will follow just one of three basic shape category. We mentioned a little bit about the ridges earlier on, and more specifically, the line angles. And a lot of times, when I’m working with students and I’m always pointing out the line angles and where the line angles are, and really, the line angle is just an imaginary line. Although we’re calling it a line angle, it’s not a really demarcated line. It’s just making reference to the junction of the two surfaces of the teeth coming together. And it’s usually a curved surface. And it really helps us define exactly the location we’re talking about. A point angle usually refers to a junction of three tooth surfaces that are coming together. And usually, it’s in a combination of those three is how we would describe this term. And again, they didn’t join up seamlessly together, but we are making a point for calling them “lines” and “points” to really talk about the location of the surface. Crest of contour or some people around the world talk about “crest of curvature.” Just to review that, what that signifies or refers to is really the widest area on the crown of the tooth. And usually, if the teeth are perfectly aligned, it’s located between the contact area of the teeth. And the widest area, the extent of the curvature really talks about where it’s most bulbous or most prominent. And the mandibular lingual aspect of the molars have the ones with the highest crest of contour or highest crest of curvature. This is significant in our instrumentations. A lot of times, I use a variety of instruments to cover that large crest of curvature. So now, I’d like to talk about some of the common numbering systems. I know everyone likes to have their own numbering system. There’s actually a few, but there are probably the three most common ones. And from the three, I say the first and the second are the most common ones. So I’d like to quickly review that before we talk about the tooth development and odontogenesis. The three numbering systems that are used worldwide, from my experiences, is the Universal System; the FDI World Federation System, or sometimes called the International Numbering System; and the third one is the Palmer notation system, which I don’t see it being used very often, but there are occasionally dental offices that still do manage to use that. So let’s start with the Universal Numbering System. The way this numbering system works is actually quite simple in that it starts with the maxillary upper right corner at the number 1. And it, successively, in a consecutive manner in a clockwise direction, increases the number up to the last molar on the maxilla, and then continues on from the lower left molar, third molar, and going on again in a clockwise direction, ending up with the number 32. So basically, it’s numbered 1 to 32 in a clockwise direction, starting from the upper right quadrant. This one is actually used very widely in the USA. And what we do for the primary numbering system under Universal is we use the letters from A to J. So for the maxillary, in the same order, and then moving on to letter K for the mandibular system. So for the permanent, we use the numbers 1 to 32. And then for the primary dentition, we start with letters A ending up with letter T for the 20 primary dentition. Next, I’m going to talk about the International System. I don’t think that nobody uses FDI as much as International Numbering System. Incidentally, the one we use in Canada, like, teach this to the students as well, is a 2-digit numbering system. And what it is the first number always refers to the quadrant. So this is quadrant 1, going on to the upper left being quadrant 2. Quadrant 3 is the lower left. Quadrant 4 is the lower right. The first number is always referring to the quadrant. The second number actually refers to the tooth number. But here’s the difference. The tooth number actually starts from the midline. So this is tooth number 1, tooth number 2, tooth number 3, moving backwards to the third molar. And same thing on the other quadrants. So we actually use the midline as our reference point for tooth number 1. And then the numbers increase as you move away from the midsagittal plane or the midline of the teeth. So upper left first molar would be quadrant number 2, and it would be tooth number 6 from the midline. And we would call it tooth number 26, unlike the Universal System where tooth number 26 is somewhere in the anterior region. So even how you phoneticize the term will signify the type of numbering system you’re using. So using “two-six,” that tells me you’re using the International System as opposed to tooth number “twenty-six,” which shows the Universal System. For primary dentition, then, actually just finishing off this point about the International System, is we use letters similar to that used for the Universal System. And the third system we want to talk about– like I said, it’s not very widely used, but we should mention about it– is the Palmer notation. And basically, what it’s doing is using this L or inverted L shape. And that is to show, to actually visually show the quadrants that you’re working on. So if it’s the upper left side, it would be L shape. If it’s the upper right, then it would be the inverted L. And then the numbers would actually signify the number 1 to 8. Or for primary dentition, it would be letter A to E. And again, just like the International System, the numbering starts from midsagittal line moving backwards. So that, in a nutshell, is a really quick review of the three numbering systems that are used globally. I want to move over to actually tooth development and odontogenesis. And really, a good review of our lectures from the university on embryology and histology. It is a complex process by which teeth grow. And there’s so many theories and suppositions on how things that we now have the science of how these embryonic cells grow and actually develop and eventually erupt in the mouth. And there are factors within the tissue and the brachial arch that are necessary for the development of the teeth. And here we go. These notes talk about how the first tooth starts forming in the sixth to the eighth week of prenatal development. So very important for the pregnant mom to have the right nutrition and the right care during those early months. It does erupt intraorally for the babies in around six months. And of course, we talked about how the primary dentition has 20 teeth. The first permanent one will probably erupt around the age six. So quick review of the life cycle of a tooth in embryogenesis. These are the different initiation factors that tooth germ will undergo to actually come and morph into this beautiful teeth that we look at intraorally every day. Just a quick review of the germ layers. There’s three germ layers, of course– the ectoderm, endoderm, and mesoderm– for our reference point to know that the teeth actually just come from the two of the three germ layers. The ectoderm really contributes to the enamel, the dentin, and the pulp; whereas, mesoderm is really key on the formation of the cementum, the periodontal ligament. This image is really showing a tooth bud just as it’s starting to form. And then you can see as it develops, it’s getting into this continuous layer of epithelium in forming a more collagenous mass that is definitely more visible. We also want to review the different shapes. There’s a bud stage, the cap, the bell, and then there’s the final maturation stage. So with those images in mind, let’s move on to actual pictorials of what these stages look like. It’s actually fascinating to see. Like in the proliferation stage, which is about 9 to 11 weeks of prenatal life, you get the cap stage forming, where the cells really multiply at that initiation stage. And you can see that the tooth germ is starting to form and really starting to shape and form a dental papilla. And so this is just a precursor to where that enamel is going to eventually reform. Then we get into the phase of histodifferentiation which is around the 14 week. This is what we normally call the “bell stage” of the formation of histogenesis. And this is actually where the dental papilla, the dental organ is going to form. There is actually a dental lamina starting to form as well. And you can see that this is really taking a shape of a bell, and hence, the terminology. Moving on to morphodifferentiation which is actually the advanced bell stage. So here, you can really identify the bell shape. And this happens around 18 weeks of prenatal life. And as you could see, it’s forming the inner enamel epithelium. And it’s also starting now the formation of dentin as well. The dental lamina is very critical and actually starts at this stage of advancement. Then we have the appositional and calcification stage. So this is getting more mature as we move along the time continuum. And the appositional phase is really this is how the manifestation, and could clearly see the amazing demarcation of the enamel and the dentin start to take shape. And it’s just fascinating to see all the odontoblast and the ameloblast now contributing to the dentin and the enamel, respectively, in the calcification stage. There are very many theories on eruption. How do teeth erupt? How do teeth know when to erupt? And what is it that marker within the body? And think most congruent theories or the acceptable norm out there is there is pressure on the roots from the erupting permanent tooth to actually push and move the primary dentition away. There is also the thought of the osteoclast, which job is to just break down everything and eat up the bone around the roots of the primary teeth that may cause movement, loosening of the primary teeth, and eventual eruption of the secondary teeth or permanent teeth. And so that notion of that successive resorption of the tooth root is absolutely something that leads to, then, the final proliferation and eruption of a permanent dentition. So quick review of the concepts we talked about. The key thing with embryology aspect of things is teeth are formed from the two germ layers. We had identified the ectoderm and the mesoderm. Mesoderm sometimes in literature is also called ectomesenchyme, but it’s really referring to that layer of the germ cell. And the enamel is always formed from the ectoderm. And the dentin, pulp, cementum, and the periodontal ligament, of course, are all derived from the mesoderm. Now, I didn’t mention some anomalies that I want to go over. And things don’t always go with plans. Just in life, same thing with tooth development. Sometimes, there could be size discrepancy. And I have a picture, actually, of a patient that was in the office last week that I’m going to share with you in the next slide showing microdontia, where teeth just will be smaller than what was normal for that jaw. Or they might be too large, and there’s not enough room in the jaw. Sometimes, we can have number discrepancies, like anadontia, where really it’s very rare to be anadontic, but sometimes, you just will have missing teeth. We’ve heard of missing premolars or retained deciduous teeth. And sometimes, with number discrepancies, you can have supernumerary. You might have an extra tooth or two. There may be some eruption disturbances of an anomaly. And that would be either premature or delayed eruption. I know, sometimes, I have moms on the chair going– my baby’s almost nine months, and there’s just no tooth in sight in the mouth. And a lot times, the question to ask is, do you remember when your teeth erupted or your husband’s teeth or your partner’s teeth erupted? Because it may just be a genetics thing, and it may just be delayed. And sometimes, they can be impacted, as we all know, with wisdom teeth– surgical impactions, horizontal impactions. Sometimes, teeth can erupt where they’re not supposed to. Ectopic eruption is absolutely a disturbance. And another anomaly is, of course, the iatrogenic disturbances as well. We can have shape discrepancies. Very, very rare, but dilaceration actually refers to the term where the root is 90 degrees to the crown. So this is a very important thing to know when we’re doing instrumentation in the patient’s mouth that the root is not where it’s supposed to be. Flexion is just showing a little divergent root from where it should normally be. And of course, the other terms reflects to a tooth inside a tooth and how sometimes it can have extra cusp on the root. And of course, the enamel pearl is another discrepancy or anomaly we should talk about. I mentioned a patient that was in my chair last week. I want you to meet Ty who has these peg laterals. And you can see, this is an example of microdontia. He is 12 years old, a cute guy. And so we’re just waiting for the jaw to really grow. He’s just turning 12, so we’re just observing with the orthodontist friend of mine, watching to see how this diastema fills up for him and how his jaw bone structure grows. But you will find peg laterals or retained teeth probably– I’d say, that’s probably the most common anomaly that I’ve seen in the dental office. So let’s talk about the four dental tissues of the mouth. These are really relating to the hard tissues of the teeth. But we’re also going to talk about the periodontium and the pulp. This is really important for our assessment. We’ve talked about how it could develop in the embryonic stage as it forms. What we see in the mouth are four dental tissues. Here we go. We have the enamel, the dentin, the pulp, and the cementum. And really, the crown is the part that’s the most visible part of the tooth, of course. And the enamel, I like to equate the enamel as like the shell of an egg, how it’s there to really protect the valuable internal, fragile organs of the mouth. And so really that’s a good analogy of what the enamel would look like. The dentin, of course, we’re going to talk in detail about that. So let’s just move on actually to the next slide which talks about the enamel. Although it is like an eggshell, I guess, it’s different from the eggshell in that it is the hardest part of the human body. It’s actually harder than human bones, too, because bone, as we know, go through osteogenesis with either osteoclastic or osteoblast or creating new bone. So unlike that, the enamel is very densely packed, calcified structure or tissue of the body. And it is very hard. It is crystallized with enamel rods. But here’s the thing, as hard and calcified as it is, it is pH soluble. At a pH of 5.5, enamel will resorb. So normal pH of the mouth is around 7, 7.2. Saliva really helps keep the pH around the base mark or the neutral mark of 7. The thing with enamel which is so unique, and this is why we need to treat it with respect, is the fact that it’s non-renewable. Once the enamel is gone, it’s not coming back. Patients are really worried about how white their teeth look. And it’s to do with the enamel. But sometimes, you do a whitening treatment, and then the teeth do change color because enamel is semitranslucent. So it actually allows the color of the dentin coming through. That’s really important, too. And as strong as the enamel is, it actually wears down by mechanical forces of just wear or tear or abuse to your enamel. So no opening beer bottles with your teeth. People do crazy things. I had a patient. She’d been with me for a while, actually. But she has a little notch on the front incisor of her enamel. And it’s for years of long hair and bobby pins. She would use her teeth to open the bobby pins. It’s crazy what people use the enamel for or abuse it, in this case. So let’s treat it with respect because it is non-renewable. And it’s so important to understand what the patient’s other environmental factors and habits are in order to help preserve them. And the simplest thing with her was just creating awareness– just saying, did you know? She says, oh my god, I had no idea that I was wearing down my enamel. And so a great educational opportunity. Pay attention, be aware. And it will get remineralized. Although it’s non-renewable, it will get remineralized with fluoride and saliva. And as we mentioned earlier on, it is protecting the very valuable pulp which has the nerve endings and the blood vessel and the nutrient supply of the tooth and, of course, the dentin. So let’s talk about the dentin and what the dentin is all about. Before we move on to that, let me just finish off with the enamel. It does withstand acids up to the pH of 5.5. So what can we do to preserve the enamel? We mentioned creating awareness in a patient of mine is a very important thing because once the damage happens, it’s permanent. But what are some of the things we could do is actually reduce the number of acidic drinks maybe the patient is exposing their enamel to. Drinking through a straw actually really helps because it’s trying to bypass that contact time between the enamel and the acid. As we all know, there’s 20 minutes of contact time after an acid exposure to the enamel where the pH really drops, and the enamel becomes very susceptible to breakage and decay eventually. Patients who don’t have enough saliva. Saliva’s an amazing buffer to neutralize the acid in the mouth. So maybe consider looking at some saliva substitute for your patients who may have xerostomia or dry mouth syndrome. And I find so many patients with medications. And 8 out of 10 of them have dry mouth as a side effect of those medications. So comprehensive medical history becomes really important in helping preserve the enamel of our patients. Fluoridated water, again, any kind of fluoride that gives a topical or systemic– depending on the patient’s risk factors, of course– is a good enamel preserver as well for us. Brushing teeth after meals using fluoridated toothpaste not only reduces the acid but giving the therapeutic benefits of the fluoride as well. Milk, cheese. Actually, patients have different lives, and we all have crazy, busy lives and don’t have time to brush right away. And so some of the strategies as you know and I’ll share with patients is maybe end your meal with something that’s not so cariogenic or acidic. So something like a slice of cheese or milk is a great buffer as well for the acid. Chewing gum. Maybe put a stick of gum in your mouth. And if it has xylitol or sorbitol, really helps with the acid reduction in the mouth; hence, enamel preservation. So enamel withstands pH of 5.5, guess what? Dentin is even harsher than that. If neutral is 7, if the environment in the oral mucosa goes anywhere slightly below 7, like 6.5, and the dentin will start to demineralize. This is really critical because dentin has a lot of innervations very close to the pulp. And so it can get sensitive for you. So patient’s primary concern, maybe today’s dental hygiene visit– my teeth have been fine, but this one area has gotten a little touchy. So what’s going on? Is there dentinal exposure to the tubules? So really watching out for the morphology of what the dentin is composed of and then explaining or helping the patient understand and then making some dietary changes that might help preserve the dentin. The big thing is the sensitivity in this area we want to really, really watch out for. The thing with dentin, though, which is different from the enamel– enamel, we said is non-renewable, but the dentin, actually, it can regenerate and it will reform over life. So that becomes really a nice thing to have. We’ve all heard of secondary and tertiary dentin formations. So the body is remarkable in that depending on the stimulus you apply to it, it may be coaxed into actually adding an extra layer of dentin. Why? Because its function is to protect itself from the pain and the hot and cold stimulus on the surface. So by adding a secondary, tertiary dentin, primary dentin layer is actually protecting the pulp from the external stimuli. And this is actually showing a closeup picture of what the dentin will look like. The reason for that sensitivity that patients are complaining about is because of the erosion causing the hypersensitivity. And the tooth will erode or wear down by actually increasing the number of tubules you have, or actually, the tubules that are exposed will just get larger in diameter, allowing for more stimulus to go through in the peritubular dentin. And as we all know, the stimulus travels to the inner structure of the pulp, where the nerves are, by the hydraulic fluid moving along the dentinal tubules. So when there’s excitement on the surface of the tooth, a lot of times, patients will have recessions. So instead of the gums covering the protective area of the dentin, the cementum, and the cementum’s eroded or worn out, now you have these exposed tubules with the stimulus going through, causing the hydraulics to move, exciting the nerve endings– the odontoblasts here– and your brain senses pain. And now, you have sensitivity in there. Moving on to the cementum which is the third structure we want to really discuss, talk about is it is definitely softer than the enamel and dentin that we’ve discussed. There’s a very thin layer. It’s bone-like. It’s hard. It covers the dentin, especially on the roots part, which is such a protective role it plays for us. And it’s very intimately connected to the periodontal ligament. So the cementum itself, actually, is not sensitive. It’s a misnomer saying, oh, my cementum’s exposed, so I have sensitivity. It’s actually the dentin getting exposed which is causing sensitivity. And it’s probably because the cementum is eroded or has been abraded somehow. The big thing with cementum is it does have a light yellow color of its own. The thickness varies, but there is that definite cellular thickness around the apex is thicker. And then it is fairly permeable as well. So patients who have clinical significance of this, such as you have recession, cementum exposure, the stain will go deeper in the cementum area than it will on the enamel area which is more stronger and densely packed. The cementum is more loose-like, and it is more permeable. So you’ll notice when patients smile or you meet someone who’s got a great smile, and if they have a really gummy smile, closer to the gum line, and if the cementum’s exposed, the teeth are a little more yellower than the biting surfaces of the teeth which are the whitest. And then the fourth area we want to, of course, talk about, and we treat this with a lot of respect, is the dental pulp. This is a living soft tissue in the innermost area of the tooth that’s rich with blood vessels, bringing the nutrient supply to the tooth. And of course, it’s carrying the nerve bundles that we’ve discussed in the realm of sensitivity. And the blood vessels are really important. A lot of times, you see– talking of coloration of teeth– patients say, yeah, you know, this tooth has just gotten so yellow now after I had a root canal done. An amazing opportunity to educate– a root canal is nothing but really removing this living tissue out of your tooth. And it’s like a dead branch of a tree. If it’s dead and there’s no nutrient supply, it snaps, and it gets brittle very easily. And this is why a lot of times, you need to put a crown over a root canal tooth because it doesn’t have any living tissue to sustain itself over time. So again, it’s important to understand that this nerve supply is very critical to the health of the tooth, long term. And it is sensitive to temperature and pressure. The pulp actually has three areas that we could break it down into the canals. There is a pulp chamber, which is the enlarged portion that you see on x-rays very easily. And the pulp horns. Sometimes it is or it’s not visible, but they are the elongations, almost like little devil’s horns that come out, and hence, the appropriate term of pulp horns. And of course, the function of the pulp– we already talked about– is there are just four key functions. It is producing a lot of dentin. And it’s helping with that secondary, tertiary dentin production that we were alluding to earlier on. So it’s really protecting the pulp. It’s really for its own preservation is that it wants to preserve itself, so it will pad on extra dentin to layer it up. It has blood vessels, of course, which gives it the nutrient function of the tooth. It has a sensory function, of course, with the nerve endings which are so varied and diverse in there that any kind of trauma to the pulp or the dentin will be perceived as pain for the patient. And of course, finally, it’s a protective function. It’s really the reparative function of the secondary, tertiary dentin by the odontoblasts. We should talk about the cemento-enamel junction and the dentino-enamel junction. So it’s fairly self-explanatory. As you’re learning from dental anatomy, everything we word, as long as the word is, if you think about it, it’s just describing the space or the location of that surface of the tooth. So cemento-enamel junction is basically the junction separating the cementum from the enamel of the tooth. This is actually within the tooth, so it’s demarcated usually around the crown of the tooth. The CEJ is something that would be visible, and you can actually clinically see it as evident. So the dentino-enamel junction is actually the junction inside the tooth, between the dentin and the enamel. So that’s not clinically visible usually. And I guess the cementum as the CEJ is something that we refer to all the time in our instrumentation as a very important anatomical landmark. And I think when we talk about CEJ and DEJ, what’s important is the difference between an anatomical crown and a clinical crown. An anatomical crown is actually a crown that goes from the incisal edge or occlusal edge, all the way to the CEJ. However, the clinical crown may or may not match an anatomical crown. In this situation here, the clinical crown is a lot longer than the anatomical crown. In this slide here, the anatomical crown pretty much mirrors what the clinical crown would be, which is from the CEJ all the way to the incisal or occlusal edge. We should talk about the periodontium as another very important aspect of tooth anatomy. The periodontium itself also has four parts– the gingiva, the alveolar bone, the periodontal membrane, and of course, the cementum. Cementum, I guess, goes on both. I put it on both sides. It’s part of the tooth, but it’s also part of the supporting periodontium structure. So the gingiva, we all know, is the oral mucosa which is really surrounding an erupted tooth. So ones have been through the histology, embryology, and eruption of the tooth. The pink lining is basically the gingiva. The bone is called the alveolar bone which has actually thickened in the tooth socket. And its function, really, is to support and surround the teeth. As much as patients come in and want their teeth cleaned and want to look all white and healthy, I always use that opportunity to show– you know, the biggest service I’m doing for you today is actually preserving what’s underneath the teeth, which is your periodontium. It’s like seeing a beautiful building that looks so amazing, but if there is cracks in the foundation, the building’s keeling over. So although, visibly, your teeth may look fine or your smile may look OK, really, the role of what we’re doing is so critical in that we’re supporting that foundation of your teeth. Periodontal ligament, of course, we all know this dense fibrous tissue which attaches, actually, the cementum to the alveolar socket of the bone. And in radiographic situations, we’re really watching out for that PDL, as we call it, to see what’s the health and integrity and clinical manifestation of that PDL. Cementum– we already talked about– is that bone-like rigid connective tissue. And that covers the root part of the tooth. And it’s very closely, intimately connected to the periodontal ligaments. Let’s talk about this review of the dental structure. So we went over a lot of the hard tissues and the soft tissue. This slide just gives you a good demarcation point of what the hard tissues are. So just for our clarity, from everything that we discussed, the enamel, dentin, cementum, and alveolar bone are the hard tissues in the dental anatomy. And of course, we have the gingiva. We have the periodontal ligament. Then we have the odontoblast layer that we talked about, the pulp chamber, the pulp canals as well as the apical foramen through which the nerve endings are moving and innervating and bringing the nutrient supply to the teeth. It’s all part of that foundation or the soft tissue of the teeth. So we started the journey with really going over and reviewing the dental classifications, the terminology of the teeth, and really the uniqueness of every tooth. That no two teeth are exactly the same. And their functions and how they look is so unique as well. We then talked about the terminology, and more importantly, the anatomical landmarks of teeth because, really, that’s where those instrumentation principles apply on a daily basis. We talked about the numbering system– what the three or actually two most common ones, being the Universal and the International systems, are. We did a quick review of our histology and embryology with the odontogenesis of the teeth and what are some of the common mishaps that can happen in the developmental phase. And then we ended this module with really talking about the soft and the hard dental tissues and really the significance of that. I would like to end the presentation by leaving you with a quote. This is a quote by Helen Keller. As we all know, Helen Keller was actually blind, and she couldn’t speak and couldn’t hear. And when asked, would you like to see the world? Would you like your vision back, Helen? And her response, which I think is phenomenal, says, “Worse than being blind is to be able to see and have no vision.” So really, we go through our lives doing what we always do, but what is our vision for our life, for our patients, for our practice? What is that goal that we want to achieve? And I think learning and continually changing and keeping up with the knowledge society and really retooling ourselves in a continual basis makes us better clinicians to, then, better provide for our patients. Thank you for joining us for this module. We’ll look forward to seeing you next time. Goodbye.

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