junctional epithelium
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The junctional epithelium (JE) is that
epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...
which lies at, and in health also defines, the base of the
gingival sulcus The gingival sulcus is an area of potential space between a tooth and the surrounding gingival tissue and is lined by sulcular epithelium. The depth of the sulcus (Latin for ''groove'') is bounded by two entities: apically by the gingival fi ...
. The probing depth of the gingival sulcus is measured by a calibrated
periodontal probe A periodontal probe is an instrument in dentistry commonly used in the dental armamentarium. It is usually long, thin, and blunted at the end. The primary purpose of a periodontal probe is to measure pocket depths around a tooth in order to establ ...
. In a healthy-case scenario, the probe is gently inserted, slides by the sulcular epithelium (SE), and is stopped by the epithelial attachment (EA). However, the probing depth of the gingival sulcus may be considerably different from the true histological gingival sulcus depth.


Location

The junctional epithelium, a nonkeratinized
stratified squamous epithelium A stratified squamous epithelium consists of squamous (flattened) epithelial cells arranged in layers upon a basal membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural i ...
, lies immediately
apical Apical means "pertaining to an apex". It may refer to: *Apical ancestor, refers to the last common ancestor of an entire group, such as a species (biology) or a clan (anthropology) *Apical (anatomy), an anatomical term of location for features loc ...
to the
sulcular epithelium The sulcular epithelium is that epithelium which lines the gingival sulcus.Carranza's Clinical Periodontology, W.B. Saunders, 2002, page 23. It is apically bounded by the junctional epithelium and meets the epithelium of the oral cavity at the h ...
, which lines the
gingival sulcus The gingival sulcus is an area of potential space between a tooth and the surrounding gingival tissue and is lined by sulcular epithelium. The depth of the sulcus (Latin for ''groove'') is bounded by two entities: apically by the gingival fi ...
from the base to the
free gingival margin The free gingival margin is the interface between the sulcular epithelium and the epithelium of the oral cavity. This interface exists at the most coronal point of the gingiva, otherwise known as the crest of the marginal gingiva. Because the s ...
, where it interfaces with the epithelium of the oral cavity. The
gingival sulcus The gingival sulcus is an area of potential space between a tooth and the surrounding gingival tissue and is lined by sulcular epithelium. The depth of the sulcus (Latin for ''groove'') is bounded by two entities: apically by the gingival fi ...
is bounded by the enamel of the
crown A crown is a traditional form of head adornment, or hat, worn by monarchs as a symbol of their power and dignity. A crown is often, by extension, a symbol of the monarch's government or items endorsed by it. The word itself is used, partic ...
of the
tooth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...
and the
sulcular epithelium The sulcular epithelium is that epithelium which lines the gingival sulcus.Carranza's Clinical Periodontology, W.B. Saunders, 2002, page 23. It is apically bounded by the junctional epithelium and meets the epithelium of the oral cavity at the h ...
. Immediately
apical Apical means "pertaining to an apex". It may refer to: *Apical ancestor, refers to the last common ancestor of an entire group, such as a species (biology) or a clan (anthropology) *Apical (anatomy), an anatomical term of location for features loc ...
to the base of the pocket, and coronal to the most coronal of the gingival fibers is the junctional epithelium. The JE attaches to the surface of the tooth by way of the EA with
hemidesmosome Hemidesmosomes are very small stud-like structures found in keratinocytes of the epidermis of skin that attach to the extracellular matrix. They are similar in form to desmosomes when visualized by electron microscopy, however, desmosomes attach t ...
s and is, on average, roughly 1 mm in width in the apico-coronal dimension, constituting about one half of the
biologic width Crown lengthening is a surgical procedure performed by a dentist, or more frequently a specialist periodontist. There are a number of reasons for considering crown lengthening in a treatment plan. Commonly, the procedure is used to expose a greate ...
. The attachment of the JE to the tooth surface can occur on enamel, cementum, or dentin. The position of the EA on the tooth surface is initially on the cervical half of the anatomical crown when the tooth first becomes functional after
tooth eruption Tooth eruption is a process in tooth development in which the teeth enter the mouth and become visible. It is currently believed that the periodontal ligament plays an important role in tooth eruption. The first human teeth to appear, the decidu ...
.


Origin

Junctional epithelium is derived from the reduced enamel epithelium (REE) during tooth development. Before the eruption of the tooth and after enamel maturation, the ameloblasts secrete a basal lamina on the tooth surface that serves as a part of the primary EA. As the tooth actively erupts, the coronal part of the fused and surrounding epithelium peels back off the crown. The ameloblasts also develop hemidesmosomes for the primary EA and become firmly attached to the enamel surface. However, the cervical part of the fused tissue remains attached to the neck of the tooth by the primary EA. This fused tissue, which remains near the cementoenamel junction (CEJ) after the tooth erupts, serves as the initial JE of the tooth, creating the first tissue attached to the tooth surface. This tissue is later replaced by a definitive JE as the root is formed.


Structure

Cells in the junctional epithelium tend to have wide intercellular spaces and fewer desmosomal junctions, to allow the transmission of
white blood cell White blood cells, also called leukocytes or leucocytes, are the cell (biology), cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and de ...
s (WBCs) from lamina propria's
blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...
s to the bottom of the gingival sulcus, to help prevent disease. In addition, the JE is also thinner than the sulcular epithelium, ranging coronally from only 15 to 30 cells thick at the floor of the gingival sulcus, and then tapering to a final thickness of 3 to 4 cells at its apical part. The superficial, or suprabasal, cells of the JE serve as part of the EA of the gingiva to the tooth surface. These superficial, or suprabasal, epithelial cells of the JE provide the hemidesmosomes and an internal basal lamina that create the EA, because this is a cell-to-noncellular type of intercellular junction. The structure of the EA is similar to that of the junction between the epithelium and subadjacent connective tissue; the internal basal lamina consists of a lamina lucida and lamina densa. This internal basal lamina of the EA is continuous with the external basal lamina between the junctional epithelium and the lamina propria at the apical extent of the JE. The EA is very strong in a healthy state, acting as a type of seal between the soft gingival tissue and the hard tooth surface. The deepest layer of the JE, or basal layer, undergoes constant and rapid cell division, or mitosis. This process allows a constant coronal migration as the cells die and are shed into the gingival sulcus. The few layers present in the JE — from its basal layer to the suprabasal, or superficial, layer — does not show any change in cellular appearance related to maturation, unlike other types of gingival tissue. Thus, the JE does not mature like keratinized tissue, such as the marginal gingiva or attached gingiva, which fills its matured superficial cells with keratin. Nor does JE mature on a lesser level like nonkeratinized tissue of the sulcular gingiva and throughout the rest of the oral cavity, which enlarges its cells as they mature and migrate superficially. The JE cells do not mature and form into a granular layer or intermediate layer. Without a keratinizing superficial layer at the free surface of the JE, there is no physical barrier to microbial attack. Other structural and functional characteristics of the JE must compensate for the absence of this barrier. The JE fulfills this difficult task with its special structural framework and the collaboration of its epithelial and nonepithelial cells that provide very potent antimicrobial mechanisms, such as the
white blood cells White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from mult ...
. However, these defense mechanisms do not preclude the development of extensive inflammatory lesions in the gingival tissue, and, occasionally, the inflammatory lesion may eventually progress to the loss of bone and the connective tissue attachment to the tooth. The JE cells have many
organelles In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the ...
in their
cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The ...
, such as
rough endoplasmic reticulum The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...
,
Golgi complex The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles insi ...
, and
mitochondria A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...
, indicating a high metabolic activity. However, the JE cells remain immature or undifferentiated until they die and are shed or lost in the gingival sulcus.
Lysosomes A lysosome () is a membrane-bound organelle found in many animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. A lysosome has a specific composition, of both its membrane prote ...
are also found in large numbers in JE epithelial cells; enzymes contained within these lysosomes participate in the destruction of bacteria contained in dental biofilm.


Pathology

The increased permeability of the JE that allows emigration of the PMN type of WBC also allows microorganisms from the dental biofilm (especially noted is ''P. gingivalis'', and associated toxins from the exposed tooth surface) to enter this tissue from the deeper lamina propria, setting up the possibility of infection to occur. Damage to the junctional epithelium results in it being irregular in texture, rather than smooth, at its surface. Most importantly is the formation of pocket epithelium within the
periodontal pocket Gingival and periodontal pockets (also informally referred to as gum pockets) are dental terms indicating the presence of an abnormal depth of the gingival sulcus near the point at which the gingival tissue contacts the tooth. Tooth gingival inte ...
, which is a histopathological characteristic of
periodontal disease Periodontal disease, also known as gum disease, is a set of inflammatory conditions affecting the tissues surrounding the teeth. In its early stage, called gingivitis, the gums become swollen and red and may bleed. It is considered the main caus ...
, having the true apical migration of the EA. In addition, there is the presence of ulceration with gingival hyperplasia, including the formation of rete ridges and connective tissue papillae at the one smooth interface of the JE with the lamina propria. Further, there is increased levels of exfoliation of epithelial cells, WBC migration, and bacterial internalization, as well as internalization-induced programmed epithelial cell death.


See also

*
Oral mucosa The oral mucosa is the mucous membrane lining the inside of the mouth. It comprises stratified squamous epithelium, termed "oral epithelium", and an underlying connective tissue termed ''lamina propria''. The oral cavity has sometimes been descri ...
*
Periodontal disease Periodontal disease, also known as gum disease, is a set of inflammatory conditions affecting the tissues surrounding the teeth. In its early stage, called gingivitis, the gums become swollen and red and may bleed. It is considered the main caus ...


References

Gingiva {{Portal bar, Anatomy