Clinical Anatomy of the Gingival Unit

| July 8, 2013 | 1 Comment

The oral mucosa is divided into three types: (1) masticatory mucosa, which includes the gingiva and hard palate; (2) lining mucosa, which consists of the alveolar mucosa, soft palate, lining of lips, cheeks, and sublingual area; and (3) specialized mucosa, which is found on the dorsum of the tongue.

 

Masticatory Mucosa (Gingiva)

The gingiva forms a protective covering over the other components of the periodontium and is well adapted to protect against mechanical insults (e.g., toothbrushing and chewing). The gingiva encircles the cervical portion of the teeth and covers the alveolar process. Anatomically, the gingiva is subdivided into the free gingiva, attached gingiva, and interdental gingiva or papilla (Figure 1-1 b). The outer surface of the gingiva consists of stratified squamous epithelium. Underneath the epithelium is gingival connective tissue, which is termed the lamina propria.

figure  (a) Schematic drawing of a tooth with its periodontium. (b) Landmarks of the gingival unit. (Left) The gingiva is salmon pink, while the alveolar mucosa is thinner and redder in color. (Right) Schematic drawing of a cross-section of the periodontium.

 

 

Free Gingiva (Marginal Gingiva)

The free gingiva or marginal gingiva surrounds the neck of the tooth. Its boundaries are, coronally, the free gingival margin; apically, the free gingival groove; and laterally, the gingival crevice and the tooth . The free gingiva is approximately 1.5 mm wide and has a smooth surface. The free gingiva lies on and adapts to the enamel and can be separated from the tooth with a periodontal instrument (Schroeder & Listgarten, 1997).

In health, the free gingival margin is the edge or the most coronal part of the free gingiva and in a fully erupted tooth is located on the enamel approximately 0.5 to 2 mm coronal to the cementoenamel junction (CEJ). In health and if teeth contact in the anterior region, the free gingival margin usually has a scalloped outline following the contour of the cementoenamel junction . If there is an open contact, the free gingival margin becomes blunted. In the posterior region, the architecture becomes less scalloped. Prior to the completed eruption of permanent teeth in children, the free gingival margin usually remains located on the cervical bulge of the enamel. This is a normal situation, and as the tooth erupts the free gingival margin will ultimately move apically.

Gingival Crevice   The gingival crevice is the space between the free gingiva and the tooth surface and is lined by nonkeratinized stratified squamous epithelium. In gingival health, the gingival crevice is termed a sulcus; once inflamed, it is termed a pocket. Healthy gingiva sulcular depth is approximately 1 to 3 mm when measured with a periodontal probe. Only in experimental conditions with germ-free animals can the sulcular depth be zero.

Gingival crevicular fluid (GCF) fills the sulcus, originates from blood vessels within the underlying connective tissue (lamina propria), and flows through the tissue into the gingival crevice. The rate of passage of this fluid is dependent upon the absence or presence of inflammation in the connective tissue of the gingiva. The flow is minimal to absent in health, but increases due to inflammation from accumulation of plaque in the gingival crevice (Alfano, 1974). Components of GCF resemble blood serum components and include elements such as calcium, sodium, potassium, and phosphorus, along with cells and bacteria. The role of GCF is both protective and destructive. While crevicular fluid flow cleanses the sulcus, it is also a source of nutrients for subgingival bacteria and supports subgingival calculus formation (Mukherjee, 1985). Certain antibiotics, including tetracyclines used in the treatment of periodontal diseases, have been found to concentrate in higher levels locally in the GCF (pocket area) than in the serum (Gordon, Walker, Murphy, Goodson, & Socransky, 1981).

 

Free Gingival Groove   The free gingival groove, a shallow depression on the outer surface of the gingiva, is about 1 to 2 mm apical from the margin of the gingiva and is slightly apical to the level of the cementoenamel junction. This groove separates the free gingiva from the attached gingiva. The free gingival groove is present in about 30 to 40% of adults and occurs most frequently in the mandibular premolar and incisor areas. It is more pronounced on the facial than on the lingual regions. Its absence or presence is not related to the health of the gingiva.

 

Attached Gingiva

The attached gingiva is continuous with the free gingiva and is firmly attached to the underlying cementum and periosteum (connective tissue) covering the alveolar process. It extends apically from the free gingival groove to the mucogingival junction (MGJ). If the free gingival groove is not present, then the landmark is at a horizontal plane placed at the level of the CEJ. The mucogingival junction joins the attached gingiva to the alveolar mucosa except on the palate because the attached gingiva runs into the palatal mucosa. The width of the free gingiva and the attached gingiva consists of the total width of gingiva.

Attached gingiva is not movable, being bound down to the bone and cementum by connective tissue fibers, making it capable of withstanding forces from toothbrushing and chewing. The width of the attached gingiva varies in different areas of the mouth and between individuals . On the facial aspect, the attached gingiva is widest in the incisor region and narrowest in the first premolar area. On the lingual aspect, the attached gingiva is widest in the molar region and narrowest in the incisor region.

Figure. Varying amounts of attached gingiva; the narrowest width is on the mandibular premolars and the widest is on the maxillary incisors.

 

The color of the gingiva is normally salmon pink with slight variations. The gingiva shows varying degrees of brownish-black color depending on ethnic variation , which is considered to be normal gingival coloring and is referred to as melanin pigmentation.

 

Figure (a) Physiological gingival pigmentation varies: light pigmentation. (b) darker, more pronounced pigmentation.

 

Stippling   Clinically, the outer surface of the attached gingiva has an appearance similar to an orange peel with shallow depressions between elevations. The free gingiva has a smooth surface and is not stippled . A histologic description of stippling is discussed in the following section.

 

Figure. Surface stippling of the attached gingiva and the interdental gingiva. Note the dimpling or depressions on the surface. The surface of the free gingiva is not stippled.

 

Stippling may be present in health or disease. The absence of stippling does not necessarily indicate the presence of disease. On the other hand, the presence of inflammation with the loss of stippling can be considered part of the disease process, assuming stippling was present initially.

Stippling is present in only about 40% of adults and varies in different individuals, ages, and sexes. Stippling of the attached gingiva is absent in children under 5 years of age and may be more evident in men than women. It is more prominent in the anterior than the posterior region and may even be absent in the molar areas. The facial gingiva shows more prominent stippling than the lingual.

 

Interdental Gingiva (Interdental Papilla)

In health the interdental gingiva tightly fills the gingival embrasure, which is the space between the contact point and alveolar bone of two adjacent teeth. The margin and lateral borders of the interdental gingiva are an extension of the free gingiva, whereas the remaining parts are attached gingiva .

 

 

Figure. Features of the interdental gingiva. (a) In health the interdental gingiva fills the gingival embrasure (G). (b) The col is directly under the contact point of the teeth.

The size and shape of the papillae are determined by tooth-to-tooth contact, the curvature of the cementoenamel junction, and the width (faciolingually) of the interproximal tooth surfaces. When teeth are crowded, often seen in mandibular incisors, the papillae may be slender and narrow. Anterior papillae are pyramidal in shape while posterior papillae are rounder and slightly flatter. An anterior papilla forms a single pyramidal structure because there is only one papilla. The papillae of posterior teeth (premolars and molars) are wedge shaped, with one vestibular (facial) and one oral (lingual) papilla connected by a concave area called the col . The col is directly apical to the contact area, representing the fusion of the interproximal junctional epithelia of two adjacent teeth. While an anterior papilla can form a col shape, it is more prominent in posterior papillae. When a diastema (loss of contact between two adjacent teeth) is present, the interdental papilla is absent, and there is no col. Since the shape of a col is concave and may not be keratinized, it may predispose the interproximal area to the accumulation of dental plaque.

Lining Mucosa

Alveolar Mucosa

Although not actually part of the periodontium, the alveolar mucosa is an important periodontal structure and deserves discussion. The alveolar mucosa extends apically from the mucogingival junction to the mucous membrane of the cheek, lip, and floor of the mouth (see Figure 1-1 b). In comparison to the attached gingiva, alveolar mucosa is thinner and redder in color, has a smooth surface, is movable, and is not keratinized.

Frenum Attachments

Frenum (plural: frena) attachments are folds of alveolar mucosa. They are not concentrations of muscle, having no more muscle fibers than alveolar mucosa. The function of a frenum is to attach lips and cheeks to the maxillary and mandibular mucosa and to limit the movement of the lips and cheeks. There are usually seven frena located in the canine/premolar area, between the central incisors and in the mandibular anterior lingual area.

Specialized Mucosa

The mucosa of the dorsum of the tongue contains numerous papillae of three types: filiform, fungiform, and circumvallate. The circumvallate papillae are located along the V-shaped groove on the back of the tongue. Each papilla is surrounded by a circular groove. The taste buds are located mainly on the sides of these papillae. The filiform papillae are slender ones and the most abundant, covering the entire top or dorsal surface of the tongue. No taste buds are associated with these papillae; they respond only to heat and mechanical stimuli. The fungiform papillae, which are broad and flat, are found chiefly at the edges of the tongue and are provided with taste buds.

 

 

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