Oral Epithelium and Junctional Epithelium

“What is oral epithelium and junctional epithelium?”

Gingiva is the part of oral mucosa that covers the alveolar process of the jaws and surrounds the neck of teeth.

Structural and Metabolic Characteristics of Oral Epithelium

Oral epithelium covers the crest and outer surface of the marginal gingiva and the surface of the attached gingiva.
On an average, the oral epithelium is 0.2 to 0.3 mm in thickness.
It is keratinized or parakeratinized or presents various combinations of these conditions. The prevalent surface, however, is parakeratinized.
Oral epithelium is composed of four layers: stratum basale, stratum spinosum, stratum granulosum and stratum corneum.
Keratinization of the oral mucosa varies in different areas in the following order: palate (most keratinized), gingiva, ventral aspect of the tongue, and cheek (least keratinized).

“Understanding the role of oral epithelium in gum health”

Keratins K1, K2, and K10 to K12, which are specific to epidermal-type differentiation, are immunohistochemically expressed with high intensity in orthokeratinized areas and with less intensity in parakeratinized areas.
K6 and K16, characteristic of highly proliferative epithelia and K5 and K14, stratifiation-specifi cytokeratins also are present.
Parakeratinized areas express K19, which is usually absent from orthokeratinized normal epithelia.
In keeping with the complete or almost-complete maturation, histoenzyme reactions for acid phosphatase and pentose-shunt enzymes are very strong.
Glycogen can accumulate intracellularly when it is not completely degraded by any of the glycolytic pathways. Thus, its concentration in normal gingiva is inversely related to the degree of keratinization and inflammation.

“Importance of studying oral and junctional epithelium for dental professionals”

Sulcular epithelium lines the gingival sulcus.
It is a thin, non-keratinized stratifid squamous epithelium without rete pegs, and it extends from the coronal limit of the junctional epithelium to the crest of the gingival margin.
It usually shows many cells with hydropic degeneration.
As with other nonkeratinized epithelia, the sulcular epithelium lacks granulosum and corneum strata and K1, K2, and K10 to K12 cytokeratins, but it contains K4 and K13, the so-called esophageal-type cytokeratins.

“Common challenges in analyzing oral and junctional epithelium”

It also expresses K19 and normally does not contain Merkel cells.
Histochemical studies of enzymes have consistently revealed a lower degree of activity in the sulcular than in the outer epithelium, particularly in the case of enzymes related to keratinization.
Glucose 6 phosphate dehydrogenase expressed a faint and homogeneous reaction in all strata, unlike the increasing gradient toward the surface observed in cornified epithelia.
Acid phosphatase staining is negative, although lysosomes have been described in exfoliated cells.

“Steps to identify layers of oral epithelium under a microscope”

Junctional epithelium consists of a collar-like band of stratified squamous non-keratinizing epithelium.
It is three to four layers thick in early life, but the number of layers increases with age to 10 or even 20 layers.
Junctional epithelium tapers from its coronal end, which may be 10 to 29 cells wide to one or two cells at its apical termination, located at the cementoenamel junction in healthy tissue.

“Asymptomatic vs symptomatic stages of epithelial damage”

These cells can be grouped in two strata: the basal layer facing the connective tissue and the suprabasal layer extending to the tooth surface.
The length of the junctional epithelium ranges from 0.25 to 1.35 mm.
The junctional epithelium is formed by the confluence of the oral epithelium and the reduced enamel epithelium during tooth eruption. However, the reduced enamel epithelium is not essential for its formation; in fact, the junctional epithelium is completely restored after pocket instrumentation or surgery, and it forms around an implant.
Cell layers that are not juxtaposed to the tooth, exhibits numerous free ribosomes and prominent membrane bound structures, such as Golgi complexes, and cytoplasmic vacuoles, presumably phagocytic.

“Role of keratinized vs non-keratinized oral epithelium”

Lysosome-like bodies also are present, but the absence of keratinosomes (Odland bodies) and histochemically demonstrable acid phosphatase, correlated with the low degree of differentiation, may reflct a low defense power against microbial plaque accumulation in the gingival sulcus.
Junctional epithelium expresses Kl9, which is absent from keratinized epithelia, and the stratifiation-specifi cytokeratins K5 and Kl4.
Another particular behavior of junctional epithelium is the lack of expression of K6 and Kl 6, which is usually linked to highly proliferative epithelia, although the turnover of the cells is very high.
Junctional epithelium exhibits lower glycolytic enzyme activity than outer epithelium, and it lacks acid phosphatase activity.

“Early warning signs of abnormal oral epithelium changes”

Junctional epithelium is attached to the tooth surface (epithelial attachment) by means of an internal basallamina. lt is attached to the gingival connective tissue by an external basal lamina that has the same structure as other epithelial—connective tissue attachments elsewhere in the body.
Internal basal lamina consists of a lamina densa (adjacent to the enamel) and a lamina lucida to which hemidesmosomes are attached. Hemidesmosomes have a decisive role in the firm attachment of the cells to the internal basal lamina on the tooth surface.
Histochemical evidence for the presence of neutral polysaccharides in the zone of the epithelial attachment has been reported.
The attachment of the junctional epithelium to the tooth is reinforced by the gingival fibers, which brace the marginal gingiva against the tooth surface.