Junctional epithelium

The junctional epithelium (JE) is that epithelium which lies at, and in health also defines, the base of the gingival sulcus. The probing depth of the gingival sulcus is measured by a calibrated periodontal probe. In a healthy-case scenario, the probe is gently inserted, slides by the sulcular epithelium (SE), and is stopped by the epithelial attachment (EA). However, the probing depth of the gingival sulcus may be considerably different from the true histological gingival sulcus depth. The junctional epithelium (JE) is that epithelium which lies at, and in health also defines, the base of the gingival sulcus. The probing depth of the gingival sulcus is measured by a calibrated periodontal probe. In a healthy-case scenario, the probe is gently inserted, slides by the sulcular epithelium (SE), and is stopped by the epithelial attachment (EA). However, the probing depth of the gingival sulcus may be considerably different from the true histological gingival sulcus depth. The junctional epithelium, a nonkeratinized 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. The gingival sulcus is bounded by the enamel of the crown of the tooth and the sulcular epithelium. Immediately apical to the base of the pocket, and coronal to the most coronal of the gingival fibers is the junctional epithelium. The JE attaches to the surface of the tooth by way of the EA 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 attachment of the JE to the tooth surface can occur on enamel, cementum, or dentin. The position of the EA on the tooth surface is initially on the cervical half of the anatomical crown when the tooth first becomes functional after tooth eruption. Junctional epithelium is derived from the reduced enamel epithelium (REE) during tooth development. Before the eruption of the tooth and after enamel maturation, the ameloblasts secrete a basal lamina on the tooth surface that serves as a part of the primary EA. As the tooth actively erupts, the coronal part of the fused and surrounding epithelium peels back off the crown. The ameloblasts also develop hemidesmosomes for the primary EA and become firmly attached to the enamel surface. However, the cervical part of the fused tissue remains attached to the neck of the tooth by the primary EA. This fused tissue, which remains near the cementoenamel junction (CEJ) after the tooth erupts, serves as the initial JE of the tooth, creating the first tissue attached to the tooth surface. This tissue is later replaced by a definitive JE as the root is formed. Cells in the junctional epithelium tend to have wide intercellular spaces and fewer desmosomal junctions, to allow the transmission of white blood cells (WBCs) from lamina propria's blood vessels to the bottom of the gingival sulcus, to help prevent disease. In addition, the JE is also thinner than the sulcular epithelium, ranging coronally from only 15 to 30 cells thick at the floor of the gingival sulcus, and then tapering to a final thickness of 3 to 4 cells at its apical part. The superficial, or suprabasal, cells of the JE serve as part of the EA of the gingiva to the tooth surface. These superficial, or suprabasal, epithelial cells of the JE provide the hemidesmosomes and an internal basal lamina that create the EA, because this is a cell-to-noncellular type of intercellular junction. The structure of the EA is similar to that of the junction between the epithelium and subadjacent connective tissue; the internal basal lamina consists of a lamina lucida and lamina densa.