Periodontal Anatomy – Junctional epithelium
The junctional epithelium (JE) is the epithelium which is located at the base of the gingival sulcus. The probing depth of the gingival sulcus is measured through the use of a calibrated periodontal probe. In healthy patients, the probe will be inserted gently, slides past the sulcular epithelium (SE), and will be stopped at the epithelial attachment (EA). The probing depth of the gingival sulcus, however may drastically differ from the true depth of the gingival sulcus.
The junctional epithelium, which is a non-keratinized stratified squamous epithelium, is located immediately apical to the sulcular epithelium. The sulcular epithelium lines the gingival sulcus from the base to the free gingival margin. At this location, it interfaces with the epithelium of the oral cavity. The gingival sulcus is surrounded by the enamel of the tooth’s crown and the sulcular epithelium. The junctional epithelium is located immediately apical to the base of the pocket, and coronal to the most coronal of the gingival fibers. The junctional epithelium (JE) attaches to the surface of the tooth through the epithelial attachment (EA). On average, the JE is roughly 1 mm in width in the apico-coronal dimension. This represents nearly half of the biologic width. The JE’s attachment to the surface of the tooth can occur on the enamel, cementum, or dentin. The position of the EA on the tooth’s surface is initially on the cervical half of the anatomical crown. This occurs when the tooth first begins to function following its eruption.
The junctional epithelium comes from the reduced enamel epithelium (REE). This occurs during the development of the tooth. Prior to the tooth’s eruption and before the enamel matures, the ameloblasts produce a basal lamina on the surface of the tooth. This acts as a part of the primary EA. As the tooth continues to erupt, the most coronal portion of the fused and surrounding epithelium will begin to peel back from the crown. In addition, the ameloblasts develop hemidesmosomes for the primary EA and firmly attach to the tooth’s enamel. The cervical portion of the fused tissue, however, remains attached to the tooth via the primary EA. This fused tissue, which is close to the cementoenamel junction (CEJ) following eruption, acts as the initial JE for the tooth. Thus creating the first tissue which is attached to the tooth’s surface. After time, the tissue is replaced by a definitive JE as the root forms.
Cells in the JE tend to have wide intercellular spaces and fewer desmosomal junctions. This allows for improved transmission of white blood cells (WBCs) from lamina propria's blood vessels to the bottom of the gingival sulcus, which ultimately aids in the prevention of disease. The JE is also thinner than the sulcular epithelium, and ranges coronally from just 15 to 30 cells thick at the floor of the gingival sulcus. At its apical part, it tapers to a final thickness of 3 to 4 cells. The superficial cells of the JE act as part of the EA on the gingiva of the tooth’s surface. The structure of the EA is similar to that of the junction between the epithelium and sub-adjacent connective tissue. The internal basal lamina contains both a lamina lucida and lamina densa.