Gingivitis and parodontitis are also diseases of the oral mucosa. If they go beyond the parodontal tissue and affect the entire mucosa, we speak of a stomatitis. If this inflammation is limited to the area of existing tooth replacement, it is called stomatitis prothetica. This could also be caused by a local allergic reaction to certain materials contained in the denture.

Thrush is a fungal infection of the mucosa. The pathogen is Candida albicans, a fungus found in almost all oral cavities. Once this disease breaks out with its whitish, wipeable mucosa coating, a basic disease should be considered which is accompanied by a weakened immune system (e.g., AIDS, leukaemia).

Epulis is tissue which proliferates from the parodontium. Depending on the proportion of blood vessels involved, the colour can be pale pink to dark red. Therapy consists of removal (excision). Epulis tends to recur. However, it may only go down spontaneously.

A leukoplakia is a whitish, non-wipeable change in the mucosa, which cannot be assigned to any other disease. Depending on its location (tongue, cheek, palate, etc.) and its surface characteristics, a leukoplakia may degenerate. It is therefore classified as a precancerosis (pre-stage cancer). A sample excision serves to clarify the degree of the threat.

Aphthae are very painful, locally limited inflamed mucosal changes in the mouth. They appear as white, lentil-sized round dots with a red edge. The causes are often unclear.

A rhagade (cheilosis or crack) is a skin fissure, e.g., at the lip or corner of the mouth, which usually heals without leaving a scar. It weeps and repeatedly tears in the mouth's corner. It may be caused by incorrect strain or medical conditions (deficiency or fungal diseases, infections). The in dental medicine most frequent causes are abraded teeth or poor tooth replacement (with the wrong bite height).

Pressure sores, pressure wounds (decubitus), pressure ulcers or necrotic changes in the mucosa (dying tissue) can develop in the oral cavity. These may be caused, for example, by orthodontal devices, badly fitted prosthetics, and strain on one part of the prosthesis due to incorrect biting.

If locally applied or even systemically dispensed, drugs may evoke side effects and damages to the mucosa. These include chemical burns caused by, for example, acids, disinfectants and substances containing alcohol or phenol. Drug-related side effects may favour or cause mucosa ulcerations, erosions and candida infections. Allergic reactions throughout the oral cavity may be caused by direct contact with the substance of a drug, dental material, oral antiseptics, drink and tobacco as well as cosmetics. Allergic contact reactions at the lips are displayed for example with inflammatory swellings, blisters and rhagades. Contact allergies at the oral mucosa are displayed with mucosal inflammation, inflammatory hyperplasia and blister formation. Additional signs may be burning, flushing, impaired sense of taste and nausea.

Certain infectious diseases also display mucosal changes, especially childhood illnesses. Symptoms found in the oral cavity may then be used for diagnostic evaluation (e.g., measles, scarlet fever, chicken pox, diphtheria, mumps, tuberculosis, syphilis).