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Bony structures of the mandible.
Hello everyone! This is Joao from Kenhub. Welcome to another tutorial. This time, I’m going to be dealing with the mandible, and we’re going to be focusing on the osteology related to this bone. Now, we’re going to be talking about bony structures, bony elements related to the lower jaw seen here, highlighted in green.
Now, the mandible is the only bone in the entire cranium that does not articulate with its adjacent skull bones via any sutures. Write this down—very important. And when the skull is observed only as a bony structure, there is nothing anatomically holding the rest of the skull and the mandible together. So as you can see and as I just mentioned, the mandible is a singular bone that has a distinctive shape, as you can see. And if you can really think for two seconds—think about a shape that resembles the mandible—yes, this looks like a horseshoe and is symmetrical on both sides.
We are going to be talking now about the articulations that are happening between the mandible and the rest of the skull. And one portion is found within the viscerocranium, which is this area that you see here highlighted in green, and dentally, you see an articulation happening between the two portions of your teeth: the lower portion and the upper portion. The lower portion being embedded within the mandible is articulating with the upper portion that is embedded within the maxilla right here, and when your mouth is closed, there is a dental articulation between the mandible and the maxilla.
Now the other articulation is happening with another portion of the skull known as the neurocranium, now seen here highlighted in green, more specifically with the temporal bones. So the temporal bone is this bone right here and is articulating here with the mandible. Now, this is a very important joint in your skull that is known as the temporomandibular joint.
Now, thanks to this relatively flexible joint, the temporomandibular joint, and the muscles of mastication, the mandible is the moving part of the jaws when the body is engaged in the feeding process. So when you’re eating, your mandible will be the moving part within your skull that allows chewing to happen.
Now, the muscles of mastication are four, mainly four, that we’re going to briefly have a look, but we’re going to cover them in way more detail in a different tutorial, and these are the muscles that you see here highlighted in green: the medial pterygoid. You have also of course a lateral pterygoid. The next one is known as the masseter (maseetŭr) or masseter (masitŭr). I’ve heard pronounced both ways. The last one is this one right here. If you can guess, yes, this is the temporal muscle or also known as the temporalis.
Now that I’m done introducing you to the mandible in general, I want to start talking about the different and specific bony structures that you find within this bone. The first one is seen here, highlighted in green already. It is known as the ramus. And keep in mind that, on the other side of the skull, you’re going to find another one. So you can say there are two rami. Rami is plural, and ramus is singular.
Now, in terms of structure, this is the second largest part of the mandible after the body and also extends cranially from this portion here known as the angle of the mandible away from the body at an angle of 110O.
Now, at the most superior point of the ramus, you can find two other structures that we’re going to be covering. On the anterior portion, you’ll find what is known as the coronoid process, and posteriorly, you’ll find this portion that articulates within the temporomandibular joint. This is known as known as the condylar process.
Now, as I mentioned, we’re going to be talking about the two structures, main structures you’ll find within the ramus or two processes that you’ll find within the ramus: the coronoid and the condylar process.
So the first one here on our list of processes that we find within the ramus is seen here, highlighted in green. It is known as the coronoid process. Now, the coronoid process, as previously mentioned, is the foremost or most anterior structure at the head of the ramus. It attaches to one muscle—this muscle right here known as the temporalis muscle, which is utilized during mastication, and as I also mentioned previously.
Although it is not directly part of the temporomandibular joint, it still aids in the various functions of the jaws such as opening and closing due to its proximity to the temporomandibular joint, and it’s involvement with its adjacent, with other adjacent structures.
Now, the other process of the ramus that we need to cover is this one seen already highlighted in green, and we talked about it. This is the condylar process. Now, the condylar process is the bony extrusion that you find on the posterior portion of the ramus as you see here on both of these images, just behind the coronoid process. So the coronoid process right about here, and we’re looking at a lateral view of the skull. And right behind it, you’ll find the condylar process which forms the lower bony component of the temporomandibular joint along with the temporal bone, which is right about here. So the joint is formed between the temporal bone and the condylar process of the mandible.
Now, the articulation happens with the articular surface of the head of the mandible—this surface right here. This is known as the surface of the head of the mandible. It is formed differently to the coronoid process because it has a much more slender stock with a greater protuberance to top it off. Now, the design creates a neck for the condyle and allows this muscle right here, the lateral pterygoid muscle, to attach to the pterygoid fovea upon it.
The other structure is this one seen here also highlighted in green, and this is the structure that separates both the condylar process from the coronoid process, and it is known as the mandibular notch.
Now, the next structure is one that we already covered briefly, the angle of the mandible seen here also highlighted, and this is where the posterior portion of the body will fuse with the ramus. Now, the body is seen right about here, and of course, the ramus that we looked at, and this is the angle a fusion between these two portions of the mandible. And this is where various structures will attach themselves to, including the muscle that you see here, the masseter (maseetŭr) or masseter (masitŭr) that is going to attach to the lateral portion of the angle of the mandible.
You also have another muscle here, and I’m turning into the posterior view of the mandible. So now, you can look at the angle of the mandible on a posterior view to show you a structure that will also attach here, the medial pterygoid muscle seen here, highlighted in green, on the right—right about here—you see here attaching to the angle of the mandible.
Now, another structure that will be attaching here is known as the stylomandibular ligament, also on the medial side.
The next structure on our list is this one seen also here, highlighted in green. It’s known as the mandibular foramen, and it’s found on the medial side of the structure that we talked about: the ramus. Now, this is an important structure because it opens into another structure called the mandibular canal, as you can see here. So this is the mandibular foramen highlighted, and you have the canal right about here. And this is an important structure, the canal, because it carries the inferior alveolar branch of the trigeminal nerve and another important structure known as the inferior alveolar artery.
Another structure to be covered here, the lingula, seen here highlighted in green as well, and this is a small shape of a triangle—you can see here—and located anteriorly to the other structure that we just covered on the previous slide, the mandibular foramen that is about here. So the lingula is almost like shadowing over the mandibular foramen. Now, this is an important structure as well because it serves as an attachment point for an important ligament known as the sphenomandibular ligament.
The next structure is known as the myelohyoid groove and is found right below or inferiorly to the lingula. Now, this is where the myelohyoid branch of the inferior alveolar nerve passes on.
Now that we just covered the main elements that we find within the ramus of the mandible, it’s time to move on to another portion of this bone known as the body. Now, the body of the mandible is large and almost rectangular in terms of shape that sits parallel or perpendicular to the floor, depending whether you’re standing upright or lying down flat respectively. Now, this part of the bone contains almost all anatomical landmarks of the mandible, which we will be talking about next.
The first one is this one, right about here, known as the oblique line and ascends from the body to the ramus of the mandible. The other structures that you will find within the body of the mandible are these seen here on the anterior or the front of the bone, and the one on the left you see is known as the mental protruberance. And then you’ll find two that are known as the mental tubercles—these two little portions here that you’ll find on the lower portion of the body.
Now, notice here that the mental protruberance is elevated on each side to form, then, of course, these tubercles, the two mental tubercles. Now, you can also see here these two images that show these structures a little bit more clearly and from a different perspective so you can find them exactly on the mandible.
The other structure is seen here. The singular is mental foramen, but you find actually two within the mandible—two mental foramina. Now, these are important structures because they transmit the two other important structures: the mental artery and the mental branch of the inferior and alveolar nerve.
We are still on the landmarks that we find within the body of the mandible, but this time, we’re looking at the inner surface, also known as the medial side of the body of the mandible, now, where we can find this oblique ridge that is known as the myelohyoid line. Now, this is an important structure because it serves as attachment point for two other structures—one, on the posterior border, which will attach to the myelohyoid line, and it is known as the pterygomandibular raphe or ligament. You probably heard both terms.
Now, the other one which kind of gives the name of this structure or the name to this structure and it’s a muscle, and the muscle is seen here, highlighted in green, known as the myelohyoid muscle.
The next structures that you’ll find also within the inner surface of the body of the mandible, these two here on these two images: on your left side, the submandibular fossa, while on your right side, you find another fossa known as the sublingual. Now, these are bony accommodation for two important glands. Of course, as the name indicates, one for the submandibular gland and the other one for the sublingual gland.
So as you can see, in anatomy, we try to keep things quite simple most of the time, not always. But either way, we try to simplify it here at Kenhub.
The next part that we find here on the body is this process or known… or also a part known as the alveolar part of the mandible or alveolar process of the mandible, which can arguably be the most important part of the bone in its entirety, especially for dentists—you know what I’m talking about—since it holds the teeth via a joint mechanism known as gomphosis.
Now, the teeth are important structures of your body as you know because they’re responsible for biting, chewing, cutting, grinding, as well as speech and pronunciation. Without them, I wouldn’t be able to do this tutorial right now. And also, they are related or they have a function related to facial tissue support.
This part of the mandible extends superiorly from the body and consists of two bony plates including the thick buccal part and a thin lingual part. Important thing that, symmetrically, each side of the mandible contains five primary teeth and seven to eight permanent teeth, depending on whether the wisdom teeth or third molars form during embryonic development.
The next structure on our list is known as the interalveolar septa – plural; septum – singular, and it’s also found within the previous structure that we talked about, the ovular process of the body of the mandible, and this is an important structure because it is separating here, as you can see, the dental alveoli.
Next on our list is this structure also found on the inner surface of the body of the mandible as we’ve seen before, and these are spines known as the mental spines. You have probably heard as well as the genial tubercles. These are found anteriorly as we see also on the inner surface of the body, and it’s important structures because it will serve as attachment points for two muscles: the genioglossus muscle, which will be attaching superiorly or in the superior mental spine, and then the geniohyoid muscle, which will be attaching, on the other hand, on the inferior mental spine.
The last structure that we’re going to be covering on this tutorial and also found within the body of the mandible is this one here, highlighted in green, and it’s known as the digastric fossa. Now, the name says it all. It’s also associated to a muscle that will use this point as an attachment area. And this is slightly lower than the mental spines, as you can also see, and found laterally. And this is where we find the digastric muscle attaching to.