Periodontology Anatomy - Junctional epithelium

The junctional epithelium (JE) is the epithelium that is located at the base of the gingival sulcus. A calibrated periodontal probe is used to measure the probing depth of the gingival sulcus. In healthy cases, the probe is slowly inserted, slides past the sulcular epithelium (SE), and is stopped by the epithelial attachment (EA). The probing depth of the gingival sulcus, however, can be considerably different from the true gingival sulcus depth.

Location

The junctional epithelium (JE) lies immediately apical to the sulcular epithelium. The sulcular epithelium lines the gingival sulcus from the base to the free gingival margin. This is where it interfaces with the epithelium of the oral cavity. The gingival sulcus is bound by the enamel on the crown of the tooth and the sulcular epithelium. The junctional epithelium is immediately apical to the base of the pocket, and coronal to the most coronal of the gingival fibers. The JE is attached to the surface of the tooth with the EA. On average, the JE is roughly 1 mm wide in the apico-coronal dimension. The attachment of the JE to the surface of the tooth can occur on the enamel, the cementum or the dentin.

Origin

The junctional epithelium comes from the reduced enamel epithelium (REE) during the development of the tooth. This occurs before the tooth erupts and after the enamel matures. The ameloblasts produce a basal lamina on the surface of the tooth which serves as a part of the primary EA. As the tooth erupts, the coronal part of the fused and the surrounding epithelium peel back off the crown. The ameloblasts also develop hemidesmosomes for the primary EA and then firmly attach to the enamel surface. The cervical part of the fused tissue, however, remains attached to the neck of the tooth through the primary EA. This fused tissue serves as the initial JE of the tooth. It also creates the first tissue that attaches to the tooth’s surface. This tissue is eventually replaced by a definitive JE once the root is formed.

Structure

Cells in the junctional epithelium typically have wide intercellular spaces and fewer desmosomal junctions. This allows the transmission of white blood cells (WBCs) from the lamina propria's blood vessels to the bottom of the gingival sulcus which helps prevent disease. In addition, the JE is thinner than the sulcular epithelium, and ranges from only 15 to 30 cells thick at the floor of the gingival sulcus. It then tapers to a thickness of 3 to 4 cells at its apical part. The superficial cells of the JE serve as part of the EA of the gingiva to the tooth surface. The structure of the EA is similar to the junction between the epithelium and subadjacent connective tissue. The internal basal lamina contains both a lamina lucida and lamina densa.

This internal basal lamina of the epithelial attachment is continuous with the external basal lamina located between the junctional epithelium and the lamina propria. In healthy patients, the EA is strong and acts as a seal between the soft gingival tissue and the hard surface of the tooth. The deepest layer of the JE undergoes continuous and rapid cell division. The few layers that are present in the JE do not show any change in cellular appearance as they mature, unlike other types of gingival tissue.