Junctional Epithelium

The junctional epithelium is the epithelium located at the base of the gingival sulcus. The gingival sulcus’ probing depth is measured with a calibrated periodontal probe. In a healthy situation, the probe is gently inserted, slides past the sulcular epithelium (SE), and stops at the epithelial attachment. However, the probing depth of the gingival sulcus can drastically vary from the depth of the true histological gingival sulcus.

Location

The junctional epithelium is located immediately apical to the sulcular epithelium and the sulcular epithelium lines the gingival sulcus from the base to the free gingival margin. This is the location where it interfaces with the epithelium of the oral cavity. The gingival sulcus is bound to the tooth through the enamel of the crown and the sulcular epithelium. The junctional epithelium is immediately apical to the base of this pocket. The junctional epithelium attaches to the surface of the tooth through the epithelial attachment (EA). In most cases, the EA is about 1 mm wide in the apico-coronal dimension. This represents nearly half of the biologic width. The attachment of the JE to the surface of the tooth can occur on the enamel, cementum, or dentin. The position of the EA on the surface of the tooth is initially on the cervical half of the anatomical crown when the tooth is functional following the tooth’s eruption.

Origin

The junctional epithelium derives from the reduced enamel epithelium (REE) which occurs when the teeth develop. Before the teeth erupt and after the enamel becomes mature, the ameloblasts secrete a basal lamina on the tooth surface which serves as a part of the primary EA. As the tooth continues to erupt, the coronal part of the fused and surrounding epithelium retracts off the crown. In addition, the ameloblasts develop hemidesmosomes for the primary EA and are securely connected to the enamel surface. However, the cervical part of the fused tissue remains attached to the neck of the tooth through the primary EA. This fused tissue, which remains near the cementoenamel junction (CEJ), serves as the initial JE of the tooth. This creates the first tissue which is connected to the tooth’s surface. One the root is established, this tissue is replaced by a definitive JE.

Structure

Cells located in the junctional epithelium often have wider intercellular spaces and fewer desmosomal junctions. This allows the transmission of white blood cells from the lamina propria's blood vessels to the bottom of the gingival sulcus and aids in preventing disease. In addition, the JE is thinner than the sulcular epithelium, and typically ranges from about 15-30 cells in thickness at the floor of the gingival sulcus. It then tapers to 3-4 cells thick at the apical portion. The superficial cells of the JE serve as part of the EA of the gingiva to the surface of the tooth. The structure of the EA is similar to the junction between the epithelium and sub-adjacent connective tissue.

This internal basal lamina of the epithelial attachment continues with the external basal lamina. It is located between the junctional epithelium and the lamina propria. In healthy patients, the EA is strong and serves as a seal between the soft gingival tissue and the tooth’s firm surface. The deepest layer of the JE, called the basal layer, undergoes continuous and rapid cell division. The few layers that exist in the JE do not demonstrate any changes in their cellular appearance when they mature. This is unlike any other form of gingival tissue.