The inside of the mouth contains multiple types of tissues with a complex variety of cellular makeups. The characteristics of the mucous membrane inside the mouth, called the intraoral mucosa, vary depending on where in the mouth it is found. The alveolar mucosa inside the cheeks and lining the bottom of the mouth is relatively delicate and free-moving. The mucosa on the palate and surrounding the teeth is firm and striated with protective, tough scleroproteins called keratin. Where these two distinct types of tissue meet is called the mucogingival junction.
There are three of these mucogingival junctions in the inside of the mouth. The first is on the exterior, or facial side, of the maxilla, or upper jaw. The second is on the facial side of the mandible, or lower jaw, and the third is on the interior, or lingual side, of the mandible. There is no mucogingival junction on the lingual side of the maxilla, as both the gingiva and the tissue of the palate are bound down and therefore not free-moving like the tissues at the other mucogingival junctions; the palate does not contain any freely moving mucosa. On the facial side of the maxilla, or bottom jaw, the mucogingival junction may be apparent where the shape of the apical edge of the teeth is visible through the gingiva; this clear contour melds into the looser, soft mucosa of the floor of the mouth at the mucogingival junction.
The mucogingival junction is important when measuring the width of the attached gingiva. Attached gingiva is firmly bound to the underlying alveolar bone and protects the mucosa during chewing and other oral functions. If there were no attached gingiva, the more fragile and mobile alveolar mucosa of the mouth would bear trauma during oral functions, including eating and brushing the teeth. The width of attached gingiva indicates the amount of protection that is provided to the other alveolar mucosa. Dental health professionals can measure the gingival sulcus, or the crevice of free gingival tissue that borders the apical edge of the teeth, using the mucogingival junction as a boundary of demarcation. A periodontal probe can determine how much of the gingiva is attached to the underlying bone, determining the depth of the gingival sulcus as demarcated by the mucogingival junction. If the periodontal probe can enter beyond the mucogingival junction, this indicates a mucogingival defect; other problems with the mucogingival junction may indicate recession of the gingiva, or the absence or reduction of keratinized tissue. Periodontal professionals may use surgical or non-surgical therapies to correct these defects and to reduce the possibility of further recession while maintaining the aesthetics and function of the teeth. These therapies include root coverage, gingival augmentation, pocket reduction, and control of etiologic factors. Because separate mucogingival conditions often occur concurrently, these therapies may be provided at the same time or in sequence. Additionally, because defects are determined in observation of changes in the mucogingival junction, it is recommended that baseline measurements are recorded and noted with each treatment.