Gingiva

Types of gingival epithelium:

Oral or outer epithelium: It covers the crest and outer surface of the marginal gingiva and the surface of the attached gingiva. It is cuboidal keratinized or parakeratinized
Sulcular epithelium: it lines the gingival sulcus. It is a thin, nonkeratinized stratified squamous epithelium without rete pegs and extends from the coronal limit of the junctional epithelium to the crest of the gingival margin. It may act as a semipermeable membrane through which injurious bacterial products pass into the gingiva and tissue fluid from the gingiva seeps into the sulcus.
Junctional epithelium: it 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. These cells can be grouped in two strata: basal and suprabasal.
Differences between the oral sulcular epithelium, the oral epithelium and the junctional epithelium:
1. The size of the cells in the junctional epithelium is, relative to the tissue volume, larger than in the oral epithelium.
2. The intercellular space in the junctional epithelium is, relative to the tissue volume, comparatively wider than in the oral epithelium.
3. The number of desmosomes is smaller in the junctional epithelium than in the oral epithelium.

Cuticular Structures on the Tooth:

Cuticular: acellular structure with a homogeneous matrix sometimes enclosed within clearly demarcated, linear borders. it include:
Acquired coatings include those of exogenous origin, such as saliva, bacteria, calculus, and surface stains.
Coatings of developmental origin are those normally formed as part of tooth development. They include the reduced enamel epithelium, coronal cementum, and dental cuticle.
After enamel formation is completed, the ameloblastic epithelium is reduced to one or two layers of cells that remain attached to the enamel surface by hemidesmosomes and a basal lamina. This reduced enamel epithelium consists of post secretory ameloblasts and cells.

Gingival Fluid (Sulcular Fluid):

The gingival sulcus contains a fluid that seeps into it from the gingival connective tissue through the thin Sulcular epithelium. The gingival fluid is believed to:
cleanse material from the sulcus,
contain plasma proteins that may improve adhesion of the epithelium to the tooth,
possess antimicrobial properties,
Exert antibody activity to defend the gingiva.


Gingival Connective Tissue:
The connective tissue of the gingiva is known as the lamina propria and consists of two layers:
A papillary layer subjacent to the epithelium, which consists of papillary projections between the epithelial rete pegs,
A reticular layer contiguous with the periosteum of the alveolar bone.
Connective tissue has a cellular and an extracellular compartment composed of fibers and ground substance.

The ground substance is amorphous, and has a high content of water. It is composed of proteoglycans, mainly hyaluronic acid and chondroitin sulfate, and glycoproteins, mainly fibronectin.

Connective tissue fibers are:

The collagen fibers: predominate in the gingival connective tissue and constitute the major components of the periodontium. Collagen fibers are produced mainly by fibroblasts but they are also may be produced by cemetoblasts and osteoblasts. The collagen fibers are bundles of collagen fibrils and these fibers in the tissue arranged in bundles.
Reticulin fibers: they are numerous near the basement membrane and surround the blood vessels.
Oxytalan fibers: present in gingiva and periodontal ligament and composed of long thin fibrils parallel to the long axis of the tooth in periodontal ligament. The function of these fibers is as yet unknown.
Elastic fibers: in the gingiva and periodontal ligament and only present in blood vessels.

The gingival fibers have the following functions:

To brace the marginal gingiva firmly against the tooth
To provide the rigidity necessary to withstand the forces of mastication without being deflected away from the tooth surface
To unite the free marginal gingiva with the cementum of the root and the adjacent attached gingiva
gingival fibers are arranged in four groups:
Gingivodental (on facial, lingual, and interproximal surfaces),
Circular (through the connective tissue of the marginal and interdental gingivae and encircle the tooth in ring-like fashion)
Transseptal (Located interproximally, the transseptal fibers form horizontal bundles that extend between the cementum of approximating teeth into which they are embedded)
Dento-periosteal fibers (are embedded in the cementum (the same portion of DGF) but run apically over the crest of the bone and terminate in the tissue of the attached gingiva.)


Cellular Elements:
Fibroblast: they are found between the fiber bundles. it synthesize collagen and elastic fibers as well as the glycoproteins and glycosaminoglycan of the amorphous intercellular substance. And regulate collagen degradation.
Fixed macrophages and histiocytes are present in the gingival connective tissue as components of the mononuclear phagocyte system
Mast cells, Adipose cells and eosinophils,

Blood Supply, Lymphatic, and Nerves:

- Three sources of blood supply to the gingiva are as follows
1. Supraperiosteal arterioles: from which capillaries extend along the sulcular epithelium and between the rete pegs of the external gingival surface.
2. Vessels of the periodontal ligament, which extend into the gingiva and anastomose with capillaries in the sulcus area.
3. Arterioles, which emerge from the crest of the interdental septa and extend parallel to the crest of the bone to anastomose with vessels of the periodontal ligament, with capillaries in the gingival crevicular areas and vessels that run over the alveolar crest.

The lymphatic drainage of the gingiva progresses into the collecting network external to the periosteum of the alveolar process and then to the regional lymph nodes (particularly the submaxillary group), In addition, lymphatics just beneath the junctional epithelium extend into the periodontal ligament and accompany the blood vessels.

Gingival innervation is derived from fibers arising from nerves in the periodontal ligament and from the labial, buccal, and palatal nerves.

Development of the dento-gingival structures:

After enamel formation is complete, the enamel is covered with reduced enamel epithelium, which is attached to the tooth by a basal lamina and hemidesmosome.
When the tooth penetrates the oral mucosa, the reduced enamel epithelium unites with the oral epithelium and transforms into the junctional epithelium.
As the tooth erupts, this united epithelium condenses along the crown, and the ameloblasts, which form the inner layer of the reduced enamel epithelium, gradually become squamous epithelial cells.
The transformation of the reduced enamel epithelium into a junctional epithelium proceeds in an apical direction without interrupting the attachment to the tooth.
The gingival sulcus is formed when the tooth erupts into the oral cavity. At that time, the junctional epithelium and reduced enamel epithelium form a broad band attached to the tooth surface from near the tip of the crown to the cement-enamel junction.


2-PERIODONTAL LIGAMENT:
It is the soft, richly vascular and cellular connective tissue which surrounds the roots of the teeth and joins the root cementum with the socket wall. In the coronal direction, the periodontal ligament is continuous with the lamina propria of the gingiva.
Periodontal fibers:
Principle fibers: it the most important element, its collagenous, arrange in bundles and follow a wavy course. It composed mainly of collagen type 1,
Sharpey's fibers: it is the terminal portion of the principle fibers that inserted into cementum and bone.
Indifferent fiber plexus: small collagen fibers associated with the larger principal collagen fibers. These fibers run in all directions forming a plexus.
Collagen: it is a protein consists of different amino acids. Its synthesis occur inside fibroblast to form tropocollagen molecules which aggregate to form microfibrils that are packed together to form fibrils. Collagen is synthesized by fibroblasts, chondroblasts, osteoblasts, odontoblasts, and other cells.

The principal fibers of the periodontal ligament are arranged in six groups:

Transseptal group: Transseptal fibers extend interproximally over the alveolar bone crest and are embedded in the cementum of adjacent teeth (These fibers may be considered as belonging to the gingiva because they do not have osseous attachment).
Alveolar crest group: Alveolar crest fibers extend obliquely from the cementum just beneath the junctional epithelium to the alveolar crest. Fibers also run from the cementum over the alveolar crest and to the fibrous layer of the periosteum covering the alveolar bone. The alveolar crest fibers prevent the extrusion of the tooth 24 and resist lateral tooth movements.
Horizontal group: Horizontal fibers extend at right angles to the long axis of the tooth from the cementum to the alveolar bone.
Oblique group: Oblique fibers, the largest group in the periodontal ligament, extend from the cementum in a coronal direction obliquely to the bone. They bear the brunt of vertical masticatory stresses and transform them into tension on the alveolar bone.
Apical group: The apical fibers radiate in a rather irregular fashion from the cementum to the bone at the apical region of the socket. They do not occur on incompletely formed roots.
Interradicular fibers: The interradicular fibers fan out from the cementum to the tooth in the furcation areas of multi rooted teeth.

Cellular Elements of periodontal ligament:

Connective tissue cells: include fibroblasts (most common), cementoblasts, and osteoblasts.
The epithelial rests of Malassez form a latticework in the periodontal ligament and appear as either isolated clusters of cells or interlacing strands. The epithelial rests are considered remnants of Hertwig's root sheath, which disintegrates during root development. They diminish in number with age by degenerating and disappearing or undergoing calcification to become cementicles. The cells are surrounded by a distinct basal lamina, are interconnected by hemidesmosomes
Defense cells: include neutrophils, lymphocytes, macrophages, mast cells, and eosinophils.
Cells associated with neurovascular elements, are similar to those in other connective tissues.
Ground substance fills the spaces between fibers and cells. It consists of two main components: glycosaminoglycans, such as hyaluronic acid and proteoglycans, and glycoproteins such as fibronectin and laminin. It also has high water content (70%).
Cementicles: it is a calcified mass, adherent to or detached from the root surfaces .and may develop from calcified epithelial rests; around small spicules of cementum or alveolar bone traumatically displaced into the periodontal ligament; from calcified Sharpey's fibers; and from calcified, thrombosed vessels within the periodontal ligament.


Functions of the Periodontal Ligament
The functions of the periodontal ligament are physical, formative and remodeling, nutritional, and sensory.
Physical Function. The physical functions of the periodontal ligament entail the following:
Provision of a soft tissue "casing" to protect the vessels and nerves from injury by mechanical forces
Transmission of occlusal forces to the bone
Attachment of the teeth to the bone
Maintenance of the gingival tissues in their proper relationship to the teeth
Resistance to the impact of occlusal forces (shock absorption)
Formative and remodeling function:
Cells of PDL participate in the formation and resorption of cementum and bone. Formative cells are (fibroblasts, cementoblasts and osteoblasts).
Nutritional and sensory functions:
The PDL supplies nutrients to the cementum, bone and gingiva by way of the blood vessels. The PDL is supplied by sensory nerve fibers transmitting tactile, pressure, and pain sensations.

Development of periodontal ligament

As the crown approaches the oral mucosa, fibroblasts become active and start producing collagen fibrils. These initially lack orientation, but they soon acquire an orientation oblique to the tooth.
The first collagen bundles appear in the region immediately apical to the cemento-enamel junction and give rise to the gingiva-dental fiber groups.
As tooth eruption progresses, additional oblique fibers appear and become attached to the newly formed cementum and bone.
The transseptal and alveolar crest fibers develop when the tooth merges into the oral cavity.

Cemental Sharpey's fibers appear first, followed by Sharpey's fibers emerging from bone. At a later stage, alveolar fibers extend into the middle zone to join the lengthening cemental fibers and attain their classic orientation, thickness, and strength when occlusal function is established.
Individual fibers consisted of two separate parts spliced together midway between the cementum and the bone in a zone that is called the intermediate plexus.