13.1. The Anatomy of the Gums 

This chapter is about the gums, which are also called gingivae (singular gingiva). The text will describe the structure of the gingiva and explain its role in periodontal diseases, from gingivitis to abscesses in humans and other mammals.

Structure

The gingiva is part of the masticatory mucosa of the mouth. This mucosa is formed by keratinized stratified squamous epithelium and it covers the dorsum of the tongue and hard palate in addition to forming the gingivae.

The gingivae surround the teeth and provide a seal around each of them. They are tightly bound to the underlying bone. This helps them resist friction against food during mastication. A healthy gingiva is an effective barrier against external threats to deeper tissue. The gingiva interfaces with the alveolar mucosa which is non-keratinized, darker and much looser as a lining of the oral cavity than the masticatory mucosa (Fig. 2). The line of contact between the gingiva and the alveolar mucosa is called mucogingival junction.

Healthy gums range from light pink to tan depending on the person’s skin color. Accumulation of bacterial plaque, however, can cause inflammation with increased redness together with swelling and a tendency to bleed. A chronic inflammation of the gingiva can affect the deeper tissue of the periodontium and potentially compromise the tooth.

The gingiva is divided anatomically into three areas called free (marginal), attached and interdental gingivae (Fig. 3).

Free gingiva

The free (also called marginal) gingiva is the edge of the gingiva, the portion where it is not attached to the tooth (“free” in this case refers to not attached). It is delimited by the free gingival groove, a shallow depression on the surface of the gum that is visible in about half of the population. This groove is most prominent in mandibular incisors, canines and premolars.

The free gingiva varies in width from 0.5 to 2 mm from the free gingival crest to the attached gingiva. The marginal gingiva has a similar appearance to that of the attached gingiva being slightly more translucent. The free gingiva lacks stippling (textured surface), however, and it is more movable for not being attached the underlying tooth. The free gingiva is stabilized by gingival fibers that have no bony support. The gingival margin, or free gingival crest is the most coronal part of the free gingiva. The gingival sulcus is the space between the free gingiva and the tooth.

Attached gingiva

The attached gingiva is continuous with the free gingiva. It is firm, resilient, and tightly bound to the underlying periosteum of alveolar bone. The facial aspect of the attached gum extends to the relatively loose and movable alveolar mucosa with the limit marked by the mucogingival junction. The attached gingiva frequently presents surface stippling, a roughened texture that derives from the organization of epithelial ridges and dermal papillae. The degree of stippling is highly variable among individuals.

The attached gingiva is widest in the incisor region (3.5 to 4.5 mm in the maxilla and 3.3 to 3.9 mm in the mandible) and narrowest in the first premolar region (1.9 mm in the maxilla and 1.8 mm in the mandible).

Interdental gingiva

The interdental gingiva (also called interdental papilla) lies between the teeth occupying the gingival embrasure, which is the close proximity space apical to the area of tooth contact. This gingiva tends to have a pyramidal shape in the vestibular and in the lingual aspects with a less extended ridge between them, forming a concave structure.

Gingival fibers

The gingiva is held firmly against the tooth by gingival fibers composed of connective tissue. These fibers differ from those of the periodontal ligament in attaching the tooth to the gingival tissue rather than to the alveolar bone.

Gingival fibers have several roles:

• They connect the base of the free gingiva to the tooth.

• They provide internal structure to the free gingiva to help it withstand the forces of mastication.

• They reinforce the connection between the free and the attached gingivae.

Damage to the gingival fibers promotes periodontitis. With reduced fiber anchorage, the gingival sulcus (labeled G in the Fig. 5) broadens and increases in depth apically. This facilitates the entrance of debris and bacteria between the root of the tooth and the alveolar bone.

Types of gingival fibers

Gingival fibers are arranged in three groups:

• Dentogingival group - there are three types of fibers within this group:

  • Fibers that extend towards the free margin of the gingiva;

  • Fibers that extend laterally to the outer surface of the gingiva; and

  • Fibers that extend laterally past the alveolar crest, and then apically along the cortex of the alveolar bone.

• Circular group - fibers found entirely within the gingiva with no connection to the tooth.

• Transseptal group - fibers that make mesiodistal connections between teeth. They are mostly found in the gingiva between teeth but also extend through the gingiva around teeth.

Summary

The gingiva is the part of the masticatory mucosa that surrounds the teeth and extends to the alveolar mucosa. It is firmly attached to the jaw bone and it has keratinized stratified squamous epithelium. The free gingiva is separated from the tooth by the gingival groove and it it very narrow. Most of the gum is the attached gingiva. The interdental gingiva occupies the cervical embrasures in healthy gums but periodontal disease may cause it to receede. Gingival fibers attach the gums to the neck of the tooth. They also provide structure to the gingiva and connect the free to the attached gingivae.

Key terms

Gingiva, gum, bacterial plaque, periodontium, periodontal diseases, free gingiva, attached gingiva, gingival fibers, gingival margin, free gingival crest, gingival sulcus, mucogingival junction, stippling, interdental gingiva, embrasure, periodontitis, dentogingival fibers, circular gingival fibers, transseptal gingival fibers.

Figure credits

Figure 1 by Ivob - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=4675607

Figure 2 Modified from original by BodyParts3D/Anatomography – http://www.nidcr.nih.gov/oralhealth/topics/oralcancer/detectingoralcancer.htm, Public Domain, https://commons.wikimedia.org/w/index.php?curid=34010997

Figure 3 Modified from original by Mohamed Hamze - taken in my private clinical practice, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3304239

Figure 4 by DRosenbach (talk). - DRosenbach (talk), Public Domain, https://commons.wikimedia.org/w/index.php?curid=8985701

Figure 5 by Goran tek-en - Own work. This vector image includes elements that have been taken or adapted from The Periodontium.jpg. This vector image includes elements that have been taken or adapted from Cross sections of teeth.svg., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=30709759