Q&A: What is junctional epithelium?
Author: Sanketh DS, MDS
Once the tooth crown is formed and ready for eruption, there is a thin membrane of cells wrapping the entire enamel surface of the tooth. This layer of cells called the reduced enamel epithelium, is a layer of flat cuboidal cells and is formed by fusion of ameloblast layer and the outer enamel epithelium. As the tooth starts to move upward and erupts through the oral mucosa, the reduced enamel epithelium fuses with the overlying oral epithelium to form the junctional epithelium or the attachment epithelium.
So, once the tooth is fully erupted, there is a dento-gingival junction established; a junction between the tooth and the gingiva. The junctional epithelium is attached to the tooth and forms a seal between the oral cavity and the underlying tissues. Above the junctional epithelium is the gingival sulcus, which is surrounded by the sulcular epithelium, a continuation of the gingival epithelium. However, unlike the gingival epithelium, the sulcular epithelium is non-keratinized and lacks rete pegs.
The junctional epithelium is a stratified non-keratinized epithelium, usually 3-4 cell layers thick but could increase in thickness as it ages. Like, rest of the oral epithelium, the junctional epithelium too, keeps proliferating in the deep layers and moves up layers to replace cells that are shed. The cells of the junctional epithelium have a high turnover with cells continuously being regenerated every 5-6 days. But, unlike oral epithelium, cells in all the layers of the junctional epithelium are incompletely differentiated. They also possess lesser number of tonofilaments and desmosomes.
Junctional epithelium is attached to the tooth surface by means of an internal basal lamina, which is composed of cells of the junctional epithlium attaching to the tooth with a hemi-desmosome. This is similar to the hemi-desmosomal junction between cells and connective tissue elsewhere in the body, but this junction is unique as cells here adhere to a calcified surface. It also has an external basal lamina, where the cells in the stratum basale of the junctional epithelium attach to the underlying connective tissue with hemi-desmosomes.
The sulcular depth ranges from 0.8mm to 3mm and this depth could increase with age or disease. Chronic inflammation as a result of either disease or ageing, could result in migration of the junctional epithelium to the cemental surface, increasing the sulcular depth, resulting in a periodontal pocket.
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