Gingiva

The gingiva is that part of the oral mucosa (masticatory mucosa) that covers the alveolar process of the jaws and surrounds the necks of the teeth. Anatomically, the gingiva is divided into—marginal, attached and interdental gingiva.

Healthy gingiva

Marginal Gingiva or Free Gingiva or Unattached Gingiva

It is defined as the terminal edge or border of the gingiva surrounding the teeth in a collar-like fashion. In some cases, it is demarcated apically by a shallow linear depression called the free gingival groove. Though the marginal gingiva is well-adapted to the tooth surface, it is not attached to it.

Blausen Tooth Anatomy

Gingival Sulcus

It is defined as the space or shallow crevice between the tooth and the free gingiva, which extends apical to the junctional epithelium. It is V-shaped and barely permits the entrance of a periodontal probe. Under normal or ideal conditions it is about 0 mm (seen only in germ free animals). The so-called probing depth of a clinically-normal gingival sulcus in humans is 2 to 3mm.

Attached Gingiva

It is defined as that part of the gingiva that is firm, resilient and tightly-bound to the underlying periosteum of the alveolar bone. On the facial aspect it extends up to the loose and movable alveolar mucosa, from which it is demarcated by the mucogingival junction. The width of attached gingiva is the distance between the mucogingival junction and the projection on the external surface of the bottom of the gingival sulcus or the periodontal pocket. It varies in different areas of the mouth, greater in the maxilla than mandible, least width in the mandibular first premolar area, greatest width in the maxillary incisor region. The width of attached gingiva increases with age and in supraerupted teeth.

Interdental Gingiva

Usually, occupies the gingival embrasure. There are three parts of interdental gingiva, facial papilla, lingual papilla and col, which is a valley-like depression that connects the facial and lingual papilla. The lateral borders and tips of the interdental papilla are formed by continuation of marginal gingiva and the intervening portion by the attached gingiva. In the presence of diastema the interdental papilla will be absent.

A diagram of the periodontium. The crown of the tooth is covered by enamel (A). Dentin (B). The root of the tooth is covered by cementum. C, alveolar bone. D, subepithelial connective tissue. E, oral epithelium. F, free gingival margin. G, gingival sulcus. H, principal gingival fibers. I, alveolar crest fibers of the periodontal ligament (PDL). J, horizontal fibers of the PDL. K, oblique fibers of the PDL.

Depiction of a person who has Halitosis

Microscopic Features

The gingiva consists of a central core of connective tissue covered by stratified squamous epithelium. Three types of epithelium exists in the gingiva.

1. The oral or outer epithelium (keratinized epithelium).
2. The sulcular epithelium
3. The junctional epithelium (nonkeratinized epithelium).

In the keratinized epithelium, the principal cell type is the keratinocyte, which can synthesize keratin. The process of keratinization involves a sequence of biochemical and morphological events that occur in a cell as it migrates from the basal layer towards the cell surface. The nonkeratinized epithelium contains clear cells, which include melanocytes, Langerhans cells, Merkel cells and lymphocytes. The oral epithelium has the following cell layers:

1. Basal layer (Stratum basale or Stratum germinativum).
2. Spinous layer (Stratum spinosum).
3. Granular layer (Stratum granulosum).
4. Keratinized cell layer (Stratum corneum).

There are three distinct differences between the oral sulcular epithelium, oral epithelium and the junctional epithelium:

• The size of the cells in the junctional epithelium is, relative to the tissue volume, larger than in the oral sulcular epithelium.
• The intercellular space in the junctional epithelium is, comparatively wider than in the oral epithelium.
• Granular layer, which is seen in the oral epithelium, is absent in sulcular and junctional epithelium.

Morphologic Characteristics of the Different Areas 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 keratinized or parakeratinized or combination of both. Keratinization varies in different areas in the following order: Palate (most keratinized), gingiva, ventral aspect of the tongue and cheek (least keratinized). The keratinized epithelium of the gingiva consists of four layers, namely stratum basale, stratum spinosum, stratum granulosum and stratum corneum.

The cells of the basal layer are either cylindrical or cuboidal and are in contact with the basement membrane. The basal cells possess the ability to divide, it is in the basal layer that the epithelium is renewed and therefore this is also called as stratum germinativum. When two daughter cells have been formed by cell division an adjacent “older” basal cell is pushed into the spinous cell layer and starts as a keratinocyte, to traverse the epithelium. It takes approximately one month for a keratinocyte to reach the outer epithelial surface where it becomes desquamated from the stratum corneum.

The basal cells are separated from the connective tissue by a basement membrane. In light microscopy this membrane appears as a zone approximately 1 μm wide and reacts positively to a PAS stain (periodic acid Schiff stain), which indicates the presence of carbohydrates (glycoproteins) in the basement membrane. In electron micrograph, immediately beneath the basal cell, an approximately 400 Å wide electrolucent zone can be seen which is called lamina lucida. Beneath the lamina lucida an electron dense zone – lamina densa is observed. From the lamina densa so-called anchoring fibrils project in fanshaped fashion into the connective tissue. The epithelial cells facing the lamina lucida contain a number of electron dense, thicker zones called hemidesmosomes. The hemidesmosomes are involved in the attachment of the epithelium to the underlying basement membrane.

Stratum spinosum consists of large cells with short cytoplasmic processes resembling spines. Since they are arranged at regular intervals they give the cells a prickled appearance. The cells are attached to one another by numerous desmosomes (pairs of hemidesmosomes), which are located between the cytoplasmic processes of adjacent cells.

Composition of a desmosome: It consists of two adjoining hemidesmosomes separated by a zone containing electron dense granulated material (GM). In addition, outer and inner leaflets of the cell (OL, IL) and the attachment plaque (AP), represent granular and fibrillar material in the cytoplasm (GM)

Stratum granulosum: Electron dense keratohyalin bodies begin to occur, these granules are believed to be related to the synthesis of keratin. Here, there is conversion of cells to “acellular” structure bordered by a cell membrane indicating keratinization of the cytoplasm of the keratinocyte.

Stratum corneum: The cytoplasms of the cells in this layer are filled with keratin and the entire nucleus is lost. But in parakeratinized epithelia, the cells contain remnants of nuclei. Keratinization is considered as a process of differentiation rather than degeneration. The keratinocytes while traversing from the basal layer to the epithelial surface undergoes certain changes.

1. From the basal layer to the granular layer both the number of tonofilaments in the cytoplasm and the number of desmosomes increase significantly.
2. In contrast, the number of organelles such as mitochondria, lamellae of rough endoplasmic reticulum and Golgi apparatus decrease.

Oral sulcular epithelium

The soft tissue wall of the gingival sulcus is lined coronally with sulcular epithelium, extending from the gingival margin to the junctional epithelium. It is made up of basal and prickle cell layer. The sulcular epithelium resembles the oral/gingival epithelium in all respects with the exception that it does not become fully keratinized. Although it contains keratinocytes they do not undergo keratinization. However, the surface cells are flattened and exhibit a tendency towards partial keratinization in response to physical stimulation. Normally, there are no regular rete pegs in sulcular epithelium but they form during the inflammation of the lateral wall.

Junctional epithelium

Denotes the tissue that joins to the tooth on one side and to the oral sulcular epithelium and connective tissue on the other. It forms the base of the sulcus. It has been examined in detail by several investigators, many hypothesis have been put forward to explain the mode of attachment of the epithelium to the tooth surface. Prior to the Gottlieb concept, it was believed generally, that the gingival soft tissues were closely opposed, but not organically united to the surface of the enamel. This concept was based on the clinical finding that the gingiva could be easily deflected from the tooth surface during instrumentation. However, experimental and clinical observations have led Gottlieb to the concept that the soft tissues of the gingiva are organically united to the enamel surface. He termed it as “epithelial attachment”. Although it was accepted generally, the concept did not explain how exactly junctional epithelium attaches to the root surface.

The junctional epithelium is attached to the tooth surface by internal basal lamina and to the gingival connective tissue by an external basal lamina. The internal basal lamina consists of a lamina densa (adjacent to the enamel) and a lamina lucida to which hemidesmosomes are attached. Various studies have also shown that junctional epithelial cells are involved in the production of laminin and play a key role in the adhesion mechanism. The attachment of the junctional epithelium to the tooth surface is reinforced by the gingival fibers. Hence the junctional epithelium and gingival fibers are considered as a functional unit, referred to as the dentogingival unit.

General structural features of junctional epithelium: It consists of a collar like band of stratified squamous non keratinizing epithelium. Thickness varies from three or four layers in early life and increases with age up to 15 to 20 layers at the base of the gingival sulcus, and only 1 or 2 cells at the most apical portion. The length of the junctional epithelium ranges from 0.25 to 1.35 mm. The cells are arranged into basal and suprabasal layers and they do not have granular layer or cornified layers. They exhibit unusual cytologic features and differ significantly from other oral epithelia. Three zones in junctional epithelium have been described, apical, coronal and middle. Apical is for germination, middle is for adhesion and coronal is permeable.

The basal cells are cuboidal or in some cases, flattened. They contain slightly more rough endoplasmic reticulum and lysosomal content. The content of mitochondria of the cells as they migrate toward and along the tooth surface decreases. Cells of the suprabasal layer especially those adjacent to the tooth surface exhibit complex microvillus formation and interdigitation. Junctional epithelial cells, especially those near the base of the gingival sulcus, appear to have phagocytic capacity.

The structural features of junctional epithelium indicate that it is highly permeable. Leukocytes and lymphocytes within junctional epithelium are seen even in clinically healthy gingiva. The densities of desmosomes that interconnect the cells are considerably less than that of oral epithelia and represents wider intercellular junctions.

Epithelium-Connective Tissue Interface

Histological sections have demonstrated that, the rete pegs of epithelial cells project deeply into the connective tissue leading to the formation of a series of interconnecting epithelial ridges. Basement membrane seems to form a continuous sheet that connects the epithelium and connective tissue. Electron microscope reveals a faintly fibrillar structure, called as the basal lamina, which is a part of the basement membrane. This structure has lamina lucida adjacent to the basal epithelial cells and lamina densa towards connective tissue. Basal lamina is produced by adjacent epithelial cells and is made up of collagenous proteins and proteoglycans binded together into a totally insoluble complex. It also contains laminin and fibronectin. Fibrils measuring 20 to 40 nm in diameter seem to extend from the basal cells through the basal lamina and into the lamina propria of the connective tissue. These structures called as anchoring fibrils are supposed to bind the basal cells, basal lamina and connective tissue together.

Supra-alveolar Connective Tissue

The connective tissue supporting the oral epithelium is termed as the lamina propria and for descriptive purpose it can be divided into two layers:

• The superficial papillary layer—associated with the epithelial ridges.
• Deeper reticular layer—that lies between the papillary layer and the underlying structures.

The term reticular here means net-like and refers to the arrangement of collagen fibers. In the papillary layer, the collagen fibers are thin and loosely-arranged and many capillary loops are present. The reticular layer is dominated by collagen arranged in thick bundles.

The lamina propria consists of cells, fibers, blood vessels embedded in amorphous ground substances.

• Cells: Different types of cells present are:

1. Fibroblast
2. Mast cells
3. Macrophages
4. Inflammatory cells

II. Fibers: The connective tissue fibers are produced by fibroblasts and can be divided into:

1. Collagen fibers
2. Reticulin fibers
3. Oxytalan fibers
4. Elastin fibers

Collagen type I form the bulk of the lamina propria and provide the tensile strength to the gingival tissues. Type II collagen is seen in the basement membrane.

The functions of gingival fibers are the following:

• It braces the marginal gingiva firmly against the tooth.
• It helps to withstand the forces exerted by mastication.
• It unites the free gingiva to the root cementum and the adjacent attached gingiva.

The arrangement of gingival fibers is described as principal group of five bundles and secondary group of minor fibers consisting of six sets.

Principal group fibers

1. Dentogingival fibers: They project from the cementum in a fan-like conformation towards the crest and outer surface of the marginal gingiva. They provide support to the gingiva by attaching it to the tooth.
2. Alveolar gingival fibers: They extend from the periosteum of the alveolar crest coronally into the lamina propria. Their function is to attach the gingiva to the alveolar bone.
3. Dentoperiosteal fibers: They arise from the cementum near the cementoenamel junction and insert into the periosteum of the alveolar bone and protect the periodontal ligament.
4. Circular fibers: They surround the tooth in a cuff or ring like fashion and course through the connective tissue of the marginal and attached gingiva.
5. Trans-septal fibers: They are located interproximally, they extend from cementum of one tooth to the cementum of the neighboring tooth. Their function is to protect the interproximal bone and maintain tooth-tooth contact.

Fibers of the secondary group

1. Periosteogingival fibers: They extend from the periosteum of the alveolar bone to the attached gingiva. They help to attach the gingiva to the alveolar bone.
2. Interpapillary fibers: They are seen in the interdental gingiva extending in a faciolingual direction and support the gingival papilla.
3. Transgingival fibers: These are seen in and around the teeth with in the attached gingiva. They maintain the alignment of teeth in the arch.
4. Intercircular fibers: They extend from the cementum on distal surface of a tooth splaying buccally and lingually around the next tooth and are inserted on the mesial surface.
5. Intergingival fibers: They are seen within the attached gingiva adjacent to the basement membrane extending mesiodistally. They provide support and contour for the attached gingiva.
6. Semicircular fibers: They extend from the mesial surface of a tooth to the distal surface of same tooth in a half circle.
7. Oxytalan fibers: They are present in all connective tissue structures of the periodontium. The function of these fibers is yet unknown.
8. Elastin fibers: Elastin fibers are only present in connective tissue of the gingiva and periodontal ligament. They are also seen in the connective tissue of alveolar mucosa in large numbers.

Extracellular matrix/ground substance

It is produced by fibroblasts, followed by mast cells and other components derived from the blood. The matrix is the medium in which the connective tissue cells are embedded and is essential for the maintenance of the normal function of the connective tissue. Thus, the transportation of water, electrolytes, nutrients, metabolites, etc. to and from the individual connective tissue cells occurs with in the matrix.

The main constituents of connective tissue matrix are protein polysaccharide matrix. These complexes are normally differentiated into proteoglycans and glycoproteins. The proteoglycans contains glycosaminoglycans, e.g: chondroitin sulfate, heparin sulfate, hyaluronic acid, etc. The proteoglycans act as a molecular filter and in addition, play an important role in the regulation of cell migration in the tissue. Due to their structure and hydration, the macromolecules exert resistance and hydration, towards deformation. Hence, when gingiva is suppressed, the macromolecule become deformed, when the pressure is eliminated the macromolecules regain their original form. Thus, the macromolecules are of importance for the resilience of the gingiva.

Blood Supply, Lymphatics and Nerves

Three major sources of blood supply to the gingiva has been described:

• Supraperiosteal arterioles: Overlying the alveolar bone along the facial and lingual surfaces, sends branches to the surrounding tissue.
• Vessels of the periodontal ligament: They extend into the gingiva and anastamose with the capillaries in the sulcus area.
• Arterioles emerging from the crest of the interdental septa.

Lymphatic drainage of the gingiva brings in the lymphatics of the connective tissue papillae. It progresses to the periosteum of the alveolar process and then to regional lymph nodes (mainly submaxillary group).

Nerve supply to gingiva is derived from fibers arising from nerves in the periodontal ligament and from the labial, buccal and palatal nerves.

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