Anatomy of the Periodontium

In order to understand how disease processes can affect the oral cavity, it is important to know the structure of the periodontium. This includes the gingival tissue and its supporting bone. The gingiva usually exhibits one of the first signs of inflammation through redness, bleeding or swelling. Although, this is not necessarily a sign of periodontal involvement it is imperative to understand the underlying structures and how they interact.

Structure of the Gingiva

The normal gingiva may range in color from light coral pink to heavily pigmented. It is normally stippled in appearance (resembling an orange peel). The makeup of the gingival tissue varies according to its location and function. There are two types of gingiva and several important anatomic regions.

  • Alveolar mucosa – The area of tissue beyond the mucogingival junction. It seems less firmly attached and redder than the attached gingiva. It is non-keratinized and provides a softer and more flexible area for the movement of the cheeks and lips.
  • Attached gingiva – This tissue is adjacent to the free gingiva and is keratinized and firmly attached to the bone structure. It can range from 3-12 mm in height.
  • Free gingiva – This tissue is not attached and forms a collar around the tooth. The trough around the tooth is called the sulcus and its depth is normally 1-3 mm. It is lined with sulcular epithelium and attached to the tooth at its base by the epithelial attachment.
  • Gingival margin – The border region of the gingiva that touches the tooth.
  • Interdental papillae – The region of gingival tissue that fills the space between adjacent teeth. In a healthy mouth this is usually knife-edged and fills the interdental space.
  • Muco-gingival junction – The scalloped line that divides the attached gingiva from the alveolar mucosa.
Figure 10. Healthy Gingiva.
healthy gingiva

Attachment Mechanism

The attachment of the tooth to the surrounding and supporting structures (bone) is accomplished through the cementum of the tooth, periodontal ligaments and the alveolar bone. The root of the tooth (cementum) is attached to the underlying bone by a series of periodontal fibers that make up the periodontal ligament and allow for minor movement of the tooth in the socket without damage to the tooth or the underlying structures. These fibers are classified apical, oblique, horizontal, alveolar crest and interradicular fibers.

Bone

The alveolar bone supports the teeth and is covered by gingival tissue. It contains several different types of bone. The inner and outer surfaces of the bone are made up of dense cortical plates. The portion between the cortical plates is called trabecular or cancellous bone. It resembles a sponge in appearance and has many irregular spaces within. The wall of the tooth socket is made of lamina dura, which is a thin, dense bone where the periodontal ligament is attached.

Figure 11. Tooth Anatomy.
basic tooth anatomy