1. Gingival epithelium:
The gingival epithelium comprise the epithelial tissue that covers the external surface of the gingiva as well as the epithelium lining the gingival sulcus and the junctional epithelium (Fig. 9).
Fig.
9 (Section courtesy of Dr. H.E. Schroeder): The gingival epithelium is subdivided
into 3 sections, the oral epithelium (OE), the
sulcular epithelium (SE), and the junctional epithelium (JE). The oral
epithelium extends from the mucogingival junction to the gingival margin. It is
continuous with the sulcular epithelium that lines the lateral aspect of the gingival
sulcus. The junctional epithelium forms the dentoepithelial junction apical to the
sulcus. Its coronal end forms the bottom of the gingival sulcus and is overlapped by the
sulcular epithelium. These epithelia differ from one another in their function and,
therefore, in some of their histological characteristics.
It is the stratified, squamous keratinizing epithelium, that lines the vestibular and
oral surfaces of the gingiva. It extends from the mucogingival junction to the gingival
margin (see Fig. 1), except for the palatal surface
where it blends with the palatal epithelium (see Fig. 7).
Fig. 10: The oral epithelium consists of a basal layer (stratum basale, SB), a spinous layer (stratum spinosum, SS), a granular layer (stratum granulosum, SG) and a cornified layer
(stratum corneum, SC). It is designed
primarily for protection against mechanical injury during mastication. Resistance to
mechanical injury is mediated primarily by the numerous intercellular junctions, mostly desmosomes, that hold the cells tightly together and
the cornified layer. The cornified layer and the relatively narrow intercellular
spaces also contribute to the relative lack of permeability.
Fig.
11 (From Karring, T. and Löe, H., 1970):
The oral epithelium is connected to the underlying connective tissue of the lamina propria by an irregular interface. This
interface consists of finger-like projections of connective tissue from the papillary
layer (arrows, Fig. 11 A) extending into depressions on the undersurface of the
epithelium. These depressions (Fig. 11 B) are located between the interconnected Rete ridges that form the undersurface of the epithelium.
Cross-sections of these ridges, as seen in histological sections are sometimes referred to
as Rete pegs.
Fig. 12: Transmission electronmicrograph of the junction between a basal cell of
the gingival oral epithelium and the connective tissue of the underlying lamina propria. 
The
epithelial cell (EC) contains widely dispersed cytoplasmic filaments, also known as tonofilaments.
The epithelial cell membrane facing the lamina propria is studded with numerous hemidesmosomes (HD) and is connected to it by a basal lamina (BL). The basal lamina consists of an electron-dense layer, the lamina densa (LD) and an electron-lucent layer, the lamina lucida (LL). The lamina densa is composed of an afibrillar type of collagen, type IV collagen. The lamina lucida is composed of laminin and other glycoproteins. Anchoring fibrils (AF), composed of type VII collagen, extend from the undersurface of the lamina densa into the lamina propria.
