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Please let us know what all subjects and topics you want to learn first. Today we would be studying the final part of oral mucous membrane, the part 4 in which we will be studying about the gingival sulcus and the dentogenival junction. So without wasting any time let's start with the topic. This is the part 4. In part 1, 2 and 3 we have studied about the basics, the non-keratinized mucosa and the keratinized mucosa. Today we will learn about the gingival sulcus and the dentogenival junction.
junction but before watching this lecture I highly recommend to watch our oral mucus membrane part 3 lecture and get thorough with the macroscopic and microscopic features of gingiva if you know gingiva by heart you will easily understand today's lecture so let's start with today's topic which is the gingival sulcus or the gingival crevice Now what is the gingival sulcus? The gingival sulcus or crevice is a narrow space between the inner aspect of the gingiva and tooth. It is a narrow space. If you can see in this diagram, it is a narrow space. between the gingiva and the tooth.
This gingival sulcus extends from the upper border of the free The gingival sulcus extends from the upper border of the free gingiva up to the dento-gingival junction, the area where the gingiva attaches to the tooth. This sulcus is a continuous space which encircles the tooth. The epithelium which lies this sulcus is called as circular epithelium.
If you can see in this diagram, this is the gingival sulcus and the epithelium which lies this sulcus is called as sulcular epithelium. This sulcular epithelium is attached to the tooth by a narrow band of epithelium which you can easily appreciate in green color and this is called as the junctional epithelium. It is that part of the circular epithelium which attaches to the tooth. This is the junctional epithelium. This circular epithelium is continuous with the gingival epithelium and the junctional epithelium.
This is the gingival epithelium, this is the circular epithelium and this is the junctional epithelium. All these three epithelium are continue with each other. And they have a common basal lamina.
If we see this circular epithelium under microscope, we can see something like this. thin and non-keratinized the circular epithelium is non-keratinized and the epithelium does not show any ridges that is its interaction with the connective tissue is plain it does not form the serpentine appearance it is straight Now the depth of the gingival sulcus is about 0.5 to 1.8 mm. On an average it is 2 mm.
Sometimes the gingival sulcus it deepens. This depth it increases in cases in which there is infection of the periodontium. Now here we have completed the portion of gingival sulcus. Now let's study what is the dentogenjival junction.
The dentogenjival junction as the name implies is the junction between the tooth and the gingiva. The junctional epithelium extends up to 2 mm on the tooth surface. We have seen this is the circular epithelium and where it attaches. to the tooth is called as the junctional epithelium.
Its length is about 2 mm and the turnover rate of the dento-gingival junction is 5 to 6 days. Now how is the structure of this dento-gingival junction? It is similar to the reduced enamel epithelium.
Here I request you all to go back to our lectures on life cycle of ameloblast, abelogenesis and enamel and brush up your knowledge about what is reduced enamel epithelium, what is miasmith membrane. Assuming that you have an understanding of all these basic terminology, let's continue what is the deltogenchival junction. The dento gingival junction, the epithelium which makes the dento gingival junction is called as the junctional epithelium.
The structure of the junctional epithelium is very simple. It is made of a single layer of basal cells and above it there are flatulent cells. There are large intercellular spaces between these cells. Now, what is the importance of these intercellular spaces? One disadvantage of this intercellular space is that bacteria and their toxins have an easy entry into the junctional epithelium making it very susceptible to infection.
But the positive point is that This open intercellular spaces or wide intercellular spaces allow neutrophils, macrophages to Langerhans cells to migrate from the connective tissue to the epithelium and thus increasing the resistance to infection. This is the structure of the junctional epithelium. Now let us see how this dento-gingival junction develops. This is a diagrammatic representation of the protective stage of life cycle of ameloblast. We have seen in that lecture that when the enamel formation is complete, if this is the enamel and the formation is complete, the ameloblast cells no longer remain columnar but they flatten out to form an irregular shaped cells.
This is and these ameloblasts then protect this enamel from coming in contact with the overlying connective tissue. This flattened layer of ameloblast is called as the reduced enamel epithelium. Now, I will show you in the diagrammatic representation.
If this is the oral epithelium, this is diagrammatic representation of an unerupted tooth. Suppose the teeth is unerupted. This is the oral epithelium below which this tooth is present.
The pink line is the reduced enamel epithelium which protects the enamel. The blue is. the enamel yellow is the dentine red is the pulp and green is the cementum now this reduced enamel epithelium covers the entire enamel surface of the unerupted tooth extending up to the cementoenamel junction. It extends up to the cementoenamel junction.
Now, what happens as the tooth erupts? As the tooth begins to erupt and approaches the oral mucosa, as we can see in this diagram, this is the oral epithelium. The tooth has started erupting and it reaches up to the oral epithelium. Now what happens is that the epithelium that covers the tip of the crown, this reduced enamel epithelium and the oral epithelium, they fuse with each other. After this fusion, the degeneration starts at the center of this fused epithelium and the crown erupts through this perforation.
The crown will erupt through this perforation. Now, Now, once the crown tip emerges in the oral cavity, as shown in this diagram, the reduced enamel epithelium is called as the primary attachment epithelium. The reduced enamel epithelium is called as the primary attachment epithelium. Once the tooth emerges into the oral cavity, the reduced enamel epithelium is called as the primary attachment epithelium.
When this process of eruption continues, a gingival sulcus is formed. This is the gingival sulcus which is formed encircling the tooth. This gingival sulcus is formed.
bound by the junctional epithelium at the base. At the base of these gingival sulcus there is junctional epithelium and there is free gingiva laterally and this is the process by which the dento-gingival junction is established. Now let us study the shift of this dento-gingival junction. The position of the dento gingival junction on the surface of the tooth is not constant throughout the life. This junction is not constant throughout the life.
When the tooth first erupts into the oral cavity, the dento gingival junction is entirely on the surface. the enamel later on as the tooth erupts the attachment epithelium separates from the enamel this separation is rapid until the tooth reaches occlusion and later on when the tooth reaches at the antagonist the separation is slow Now we will study about two important terminology. What is the active eruption and what is passive eruption? The actual movement of the tooth towards the occlusal plane is called as active eruption. Once the tooth reaches the occlusal plane, the separation of the primary attachment epithelium from the tooth is called as passive eruption.
Initially, the reduced enamel epithelium attaches the gingiva to the tooth. Gradually, this reduced enamel epithelium is lost and oral epithelium contacts the tooth surface. Now this reduced enamel epithelium is called as the primary attachment epithelium.
Initially when the tooth erupts in the oral cavity, the gingiva is bound to the tooth by this primary attachment epithelium. Gradually this reduced enamel epithelium is lost and the gingival epithelium attaches the gingiva to the tooth. And this gingival epithelium is called as secondary attachment epithelium.
Now the shift of the dento-gingival junction occurs in stages. In stage 1. There are four stages. In stage 1, the gingival sulcus is on the enamel covered crown. We can see the gingival sulcus is on the enamel and the apical end of the attachment epithelium is on the cemento enamel junction. This kind of epithelial attachment can be seen in all the primary teeth and permanent teeth up to 20 to 30 years of age.
In stage 2 the bottom of the gingival sulcus is still on the enamel. And the apical end of the attachment epithelium is partly on the cementum and partly on the enamel. Clear? In the stage 3, what happens is that the bottom of the gingival sulcus comes on the CEJ.
While the epithelial attachment is entirely on the cementum. This is a very slow process. It represents a body's attempt to maintain the intact dentogenjival junction.
What happens in stage 4? This is in stage 4 recession of the gingiva occurs. The entire epithelial attachment is on the cementum and this occur in 50 to 70 years of age.
Here we can see the entire epithelial attachment is on the cementum. Now let us study what is anatomic crown and what is clinical crown. Anatomic crown, the part of the tooth covered by enamel is called as anatomic crown.
This is anatomic crown. Now, what is clinical crown? The part of the crown visible in the oral cavity is clinical crown. The entire enamel covered crown is not seen in the oral cavity.
Part of it is covered by the free gingiva. crown under ideal condition is smaller than the anatomic crown. So as we have studied about stage 1, 2, 3 and 4 of shift of the dendrogen-gevel junction. In stage 1 and 2 the clinical crown is less than the anatomic crown which is very physiologic In stage 3 the clinical crown and the anatomic crown is of same dimension which is pathologic And in stage 4 the clinical crown is more than the anatomic crown which is again pathologic So here we complete the oral mucous membrane chapter. In the next lecture, we will be studying about cementum.
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