Structure of the tooth seen in crossection.
Hi everyone! It's Nicole from Kenhub here, and welcome to our tutorial on the anatomy of the tooth. So, thanks for joining me in today's lecture about the tooth and I want to begin just by talking a little bit about why we have a tutorial on the tooth and how much we're going to go into it.
So, knowledge of the anatomy of the tooth is, of course, important to help maintain good oral health. But while it's important particularly for dentists, it's also a topic that every doctor or healthcare provider should get to know. I know in my training, it was skimmed over a little bit so I think this tutorial will be able to help clear a few things up. So, in this tutorial, we will go over this image of the tooth and we'll use this image to talk about different parts of the tooth and its different structures including the periodontal structures which are the structures that support the tooth. But, before we begin, let's have a little bit of a chat about the development and function of the tooth.
So, a tooth is a small calcified structure located within the jaw of human beings. From a histological point of view, the tissue composition of the tooth is found normally only within the oral cavity and is limited to the dental structures. And the main function of the tooth is to break down food into smaller pieces in a process called mechanical digestion, and is therefore considered to be a part of the upper digestive system.
Human beings are diphyodont, which means that they develop two sets or two generations of teeth. And the first set or generation of teeth is referred as the deciduous dentition while the second set is known as the permanent dentition. The complete set of deciduous dentition is twenty whereas the complete set of permanent dentition is usually around thirty two, sometimes less.
The deciduous dentition is usually complete by the age of three and by the age of six, we begin exfoliating, which is when our deciduous teeth are lost in replacement of the permanent teeth. And all permanent teeth will usually have erupted – which means to become visible in the mouth – between the ages of eighteen and twenty one. There are many different types of teeth but we'll cover that in a different tutorial. And, on our slide, we just have the text describing what we said about the deciduous and permanent dentition. So, our deciduous dentition has twenty teeth and our permanent dentition has thirty two.
So, now let's move on to looking at the different parts of the tooth and the first part we're going to look at here is the crown which we can see here highlighted in green. And it's probably a good time to note that this image is of a molar tooth here which is a tooth located at the back of the mouth; the other teeth being premolars, canines and incisors. And as you all probably have noticed in your mouth, the other teeth have different shapes for their different functions. These mainly being tearing and crushing of food. But here with our molar, we can see that it's shaped a bit large and flat and it's mainly used for grinding.
The bulk of the crown is composed of dentin or dentine, which is a calcified tissue of the body with the pulp chamber within. And I'll just point out to you with my mouse where the dentin is. This is sort of beige layer so inside of the enamel but surrounding the pulp chamber. An important thing to remember here is that before the tooth erupts, the crown is enclosed within bone, but after the eruption, the crown is almost always visible and dentists often refer to two types of crowns – an anatomical crown which is the part of the tooth covered by enamel and a clinical crown which is the part of the tooth visible above the gum line and which I'm pointing out just here.
So, as I've just mentioned, the crown is covered by a hard translucent tissue called enamel which is this green section here. An enamel is the hardest substance in the body and consists mostly of a mineral called hydroxylapatite which is a stored form of calcium and phosphorus around about 95%. And just to note that hydroxylapatite is also referred to as hydroxyapatite without the L for those of you reading other materials. An enamel varies in color from light yellow to white.
And now we're coming to our image of our tooth with the dental root highlighted. And the dental root along with the crown is the other major part of the tooth. The dental root is the lower part of the tooth that inserts into the underlying bone to anchor the tooth in place. And the tooth can have any number of roots from one to four, occasionally five, although in this image, we can see that there are only two – this root over here and this one behind the gingiva just here.
Now, the dental root is covered by a calcified substance we call cementum. Now, cementum is histologically different from enamel but it acts as its equivalent from just below the gingival line and, as we can see, covers the entire root of the tooth. The meeting point between the enamel and the cementum is known as the cementoenamel junction which we can see just here. And like enamel, cementum contains hydroxylapatite around about 65%.
The crown and the root of the tooth meet at a point known as the neck of the tooth. This is also known as the cervical margin and this is an important landmark as it's a landmark for orthodontists and surgeons who are considering the movement of the tooth.
So as we've mentioned before, immediately below the enamel and the cementum, there is another tissue which is known as dentin. And like these tissues, it also consists mostly of hydroxylapatite around about 70%. And it's probably important to note here that the color of dentin is yellow and actually contributes significantly to the color of our teeth as the overlying enamel is translucent. The main function of dentin is to support enamel and to add another supportive layer to the tooth. The enamel and the dentin must be intact in order for the tooth to stay alive and healthy as once any bacteria enters the pulp chamber, the damage is irreversible. And it might be important to note now that it's also softer than enamel but it's harder than cementum.
And now we're coming to our image of the pulp chamber. So, as we can see in this image, below the dentin is a hollow space that contains nerves, blood vessels and connective tissue, and this wide space in the coronal portion of the tooth is referred to as the pulp chamber. And the shape of the pulp chamber corresponds to the overall shape of the tooth and, therefore, each tooth has a different shaped pulp chamber.
Now, in this image here, we can see the pulp chamber continuing inside the dental root as a hollow canal which we can see here and this is known as the root canal which is an anatomical space that carries blood vessels and nerves to the teeth. And I'm sure you've all heard the joke about having to go to the dentist to have a root canal treatment done before the idea that that you have to go to a dentist to get a very painful root canal. Well, the reason why this is so painful is generally because the enamel has worn away through either decay or a break, and the bacteria have entered not only the pulp chamber with their nerves and blood vessels to create inflammation and infection but also into the root canal. And if this infection is not treated, it can create an abscess down here in the root which is extremely painful. So, the number of root canals within a tooth is dependent on the number of roots within the tooth but they're usually being one root canal to each root. And as we can see in this image, we have a single root canal making its way down a single root.
And as we mentioned before going off topic, the pulp chamber and root canals both contain dental pulp which is one of the four main tissues or substances that make up the tooth along with enamel, cementum and dentin which we mentioned earlier. And this dental pulp is a little bit special as it also contains odontoblasts, which are cells that are responsible for producing dentin.
So now we're going to talk a little bit about the blood supply of the tooth and we've talked before about how the blood vessels and nerve supply come up through the root canal into the pulp cavity. So, in the slide, I wanted to talk about the arteries that do the supplying which are, of course, called the dental arteries or the alveolar arteries. Now, we can see them in green on this slide. And these arteries are a branch of the maxillary artery which is a branch of the external carotid artery.
So, let's look at this text here. So we're going from the external carotid artery to the maxillary artery which then branches into the dental or alveolar arteries. And to divide the branches further, we have the upper teeth being supplied by two superior alveolar arteries namely the anterior and posterior superior arteries and the lower teeth being supplied by the inferior alveolar artery. But do remember that all of these arteries are branches of the maxillary artery.
And in addition to the arteries inside the pulp chamber and the root canal, we, of course, have the dental veins which again are green on this slide. And, generally speaking, the veins of the upper and lower teeth follow the corresponding arteries. So our superior alveolar or dental veins for the upper teeth and inferior alveolar or dental veins for the lower teeth. And these veins drain mainly into the pterygoid plexus or the facial vein.
And, of course, we also have the nerves running through the root canals and these are the dental branches that you can see now in green. And all of our teeth are innervated by branches of the fifth cranial nerve which is the trigeminal nerve. And, once again, if we have a look at our text here, the upper teeth are innervated by the superior alveolar nerves. So, as we can see, we have the trigeminal nerve which branches into the maxillary nerve which then branches into the superior alveolar nerves and the lower teeth are innervated by the inferior alveolar nerve. So, if we go down on nerve trunks, we can see the trigeminal nerve branching into the mandibular nerve which then branches into the inferior alveolar nerve.
And now after all that branching, we're just going to have a little bit of a chat about one very small aspect of the tooth – the apical foramen of the tooth. And we can see that tiny opening in green just here. And this is important as all the vessels and nerves of the tooth enter or exit by this small opening in the root and it also represents the junction between the pulp and the periodontal tissue which are the structures which support the tooth, and the structures which we are going to talk about in the next few slides.
So, I'm just going to pause to say thanks for sticking with me for this long and I hope you're enjoying our tutorial on the tooth. So, here we are with our image of the gums highlighted in a very bright green here, and the gums are also called the gingivae. The gingivae are periodontal tissues and are specialized regions of the oral mucosa that surround the teeth, and their function is to provide a seal around them. And the gingivae are attached to the underlying bone as we can see in this image.
So, we're going to have a look at some images of different sections of the gums and where they attach. So, in our first image, we can see the pars fixa of gums which are the part of the gums that attach to the teeth. And, as we can see, these are the areas that adhere directly to the teeth, just here and here. And, also, we have the pars libera of gums which are areas where the gums are free and not attached to the teeth as we can see in this little section just here in between the teeth.
The gums also consist of a nonkeratinized stratified squamous epithelium with an underlying lamina propria shown here in green. And it's probably a good time to note that, together, the epithelium and lamina propria are referred to as a mucosa. So, the gums can also be considered a mucosal tissue and the lamina propria is attached to the underlying bone of the maxilla or mandible which is referred to alveolar bone which we can see just here.
Now looking at this image, we can see our interdental papilla or the interdental gingiva which are the part of the gums which fill the space between the teeth. And the function of the interdental papilla is to prevent food impaction and we can see this little area between the two molars just here.
And the final structure we'll look at out of the periodontal tissues is the periodontal ligament, and this ligament attaches the tooth to the underlying alveolar bone and functions as a supporting structure. And its function is to help the process of tooth eruption as well as provide sensory information about tooth position.
So, again, thanks for sticking with me for this long, and now, we're on our final slide. So, to finish off this tutorial, let's have a look at some clinical notes which are relevant to the tooth. So, knowledge of acute dental trauma is a very useful thing to know in the emergency department as sometimes you'll see acute presentations of dental injuries or diseases. Now, you're probably wondering what kind of presentation would I see in the emergency department considering that these are just teeth. But the things that you're going to see most likely are fractures, and fractures of the teeth can be classified into categories using the Ellis classification system which is a way of classifying dental fractures according to various injuries such as whether it's to do with the underlying structure or whether it's just surface damage. And though there are nine classes, we are only going to talking about three right now. And these are Ellis I fractures which are crown fractures that involve the enamel, Ellis II fractures which involve the enamel and dentin, and Ellis III fractures which involve the enamel, dentin and dental pulp. And when the dental pulp is exposed, infection of the pulp may develop which is known as pulpitis.
There are also diseases that can infect the periodontal structures and these are called periodontal diseases. The most common periodontal disease is gingivitis or inflammation of the gums caused by bacterial biofilms which are also known as plaque. Gingivitis is usually reversible but if it is not controlled, it can lead to periodontitis which in turn can lead to tooth loss.
And that concludes our tutorial on the anatomy of the tooth. Thanks for watching.
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