It is the stratified non-keratinizing epithelium, that surrounds the tooth like a collar with a cross-section resembling a thin wedge ( Fig. 1 and Fig.9). It is attached by one broad surface to the tooth and by the other to the gingival connective tissue. The junctional epithelium has 2 basal laminas, one that faces the tooth (internal basal lamina) and one that faces the connective tissue (external basal lamina). The proliferative cell layer responsible for most cell divisions is located in contact with the connective tissue, i.e. next to the external basal lamina. The desquamative (shedding) surface of the junctional epithelium is located at its coronal end, which also forms the bottom of the gingival sulcus.
The junctional epithelium is more permeable than the oral or sulcular epithelium. It serves as the preferential route for the passage of bacterial products from the sulcus into the connective tissue and for fluid and cells from the connective tissue into the sulcus.
The term epithelial attachment: refers to the attachment apparatus, i.e. the internal basal lamina and hemidesmosomes, that connects the junctional epithelium to the tooth surface. This term is not synonymous with junctional epithelium which refers to the entire epithelium.
Fig. 20: Segment of junctional epithelium (JE) from an area just apical to the gingival sulcus. The width of the junctional epithelium may consist of as many as 30 cells in the sulcus region to as few as one cell in its most apical portion. The intercellular spaces between the cells of the junctional epithelium are wider than in the oral or sulcular epithelia. This is due in part to the lower density of intercellular junctions between the cells of the junctional epithelium. The density of junctions is approximately one third of that in the oral and sulcular epithelium.
This section is unusual by the absence of inflammatory cells in the connective tissue adjacent to the epithelium.
Fig. 21:
Transmission electronmicrograph of normal, uninflamed junctional epithelium (JE).
The cells are orientated with their long axis parallel to the tooth surface. The
intercellular spaces are relatively narrow. The epithelium is attached to the enamel
by an internal basal lamina (IBL) and to the
connective tissue (CT) by the external basal lamina
(EBL). ES, enamel space.
The cytoplasm of the junctional epithelium contain dispersed
tonofilaments, but lack tonofibrils. Under normal circumstances these cells do not
undergo keratinization.
Fig. 22: Transmission electronmicrograph of junctional epithelium in inflamed
gingiva. Note the marked distension of the intercellular spaces by polymorphonuclear leucocytes (PMN)
that are migrating from the connective tissue toward the gingival sulcus (located
toward the top of the micrograph). Fluid exudate from the connective tissue also flows
into the sulcus through the enlarged intercellular spaces. The spaces enlarge in
part through rupture of the desmosomal junctions and in part because they become distended
by inflammatory cells and fluid.
Fig. 23: The bi-directional arrows indicate that the junctional epithelium (JE) is
the most permeable portion of the gingival epithelia. Soluble substances can diffuse
from the oral cavity into the underlying gingival connective tissue (CT), while both
fluids and cells can travel through the junctional epithelium from the connective tissue
into the gingival sulcus (S) on their way to the oral cavity. Because of its
permeability to bacterial products and other assorted antigens originating in the oral
cavity, the connective tissue adjacent to the junctional epithelium tends to become
infiltrated with chronic inflammatory cells, primarily lymphocytes and plasma cells. OE,
oral epithelium; SE, sulcular epithelium.
Fig. 24: Diagram of a mesio-distal section through the interdental gingiva. This drawing corresponds to a cross-section of the interdental gingiva shown in Fig. 8 B. The junctional epithelium (JE) forms a collar around the apical border of each adjacent tooth. The junctional epithelia of the adjacent teeth are united in the most coronal part of the interdental space, near the interdental gingival margin (GM), or "col". Following histological processing, the enamel of the crowns is lost, leaving an enamel space (ES). AB, bone of alveolar process; AC, alveolar crest; CE, cementum; CEJ, cemento-enamel junction; GF, gingival fibers in cross-section; PDL, periodontal ligament; TF, transseptal fiber group.
