The junctional epithelium is that epithelium which lies at, and in health also defines, the base of the gingival sulcus. It attaches to the surface of the tooth with hemidesmosomes and is, on average, roughly 1 mm in width in the apico-coronal dimension, constituting about one half of the biologic width.
The junctional epithelium, a non-keratinized stratified squamous epithelium, lies immediately apical to the sulcular epithelium, which lines the gingival sulcus from the base to the free gingival margin, where it interfaces with the epithelium of the oral cavity.
Cells in the junctional epithelium tend to have wide inter-cellular spaces, to allow the transmission of white blood cells from blood vessels to the bottom of the gingival sulcus, to help prevent disease. Damage to the junctional epithelium results in it being irregular in texture, rather than smooth, and the formation of "pocket" epithelium, which is a histopathological characteristic of gum disease.