The oral mucosa lines the oral cavity as a protective layer. Different diseases and chronic stimuli can lead to changes in the oral mucosa.
What is the oral mucosa?
The oral mucosa is the mucosal layer (tunica mucosa) that lines the oral cavity (cavum oris) and consists of a multilayered, partially keratinized squamous epithelium. Depending on its function and structure, a distinction is made between the lining, masticatory (relating to the chewing process or mastication) and specialized oral mucosa. In a healthy state, the oral mucosa has a pinkish surface. Various impairments of the oral mucosa lead to changes in structure and surface texture, which can present clinically in a very heterogeneous manner.
Anatomy, composition, and structure
The oral mucosa can be divided into a lining, masticatory, and specialized mucosal layer depending on function and structural composition. The lining layer of the oral mucosa, which is approximately 0.1 to 0.5 millimeters thick, consists of nonkeratinized squamous epithelium. This proportionally largest oral mucosal layer accordingly contains no keratin-containing epithelial cells. It lines the velum palatinum (soft palate), the underside of the tongue, the processes of the alveoli (tooth compartments) and the floor and vestibule of the mouth. In the oral vestibule, the oral mucosa also forms a deep enveloping fold, while in the alveolar processes it merges into the gingiva (gums). The masticatory layer of the oral mucosa is about 0.25 millimeters thick, is composed of keratinized squamous epithelium, and can be further subdivided into a stratum basale (basal layer), stratum spinosum (prickle cell layer), stratum granulosum (granule cell layer), and a stratum corneum (horny cell layer). The masticatory mucosal layer is located at the palatum durum (hard palate) and in the gingival area. The specialized oral mucosa lines the dorsum of the tongue and is composed of a keratinized squamous epithelium in which so-called papillae, wart-like elevations that function as taste buds, are embedded.
Function and tasks
The oral mucosa serves first of all to line and delimit the oral cavity. In addition, it performs several functions on which the specific structure of the oral mucosa depends. Thus, the three types of oral mucosa each fulfill their specific function. The portion of the oral mucosa that covers the gums and palate is thick and highly keratinized, as this is subjected to heavy stress during the chewing process. The oral mucosa, which lines the underside of the tongue, the floor and vestibule of the mouth, and the cheeks and lips, is characterized by its elasticity and is unkeratinized. In addition, sensory receptors are embedded in the oral mucosa, which control the sensation of pain, touch and temperature. In particular, the specialized mucosal layer of the oral mucosa contains wart-like elevations, the so-called papillae, which are located at the back of the tongue and serve as taste buds for the perception of taste. The oral mucosa is also responsible for the defense against pathogens and contains glands that participate in the production and secretion of saliva. Saliva is involved in the predigestion of carbohydrates, protects the oral mucosa from mechanical or bacteriological influences, and neutralizes toxins, among other functions.
Diseases, ailments and disorders
Diseases of the oral mucosa may manifest as a result of local processes (injuries, infections), higher-level dermatoses (skin disease), or as a result of underlying systemic disease. Chemical or physical irritants and/or viral or bacterial infectious agents may cause inflammatory changes of the oral mucosa (stomatitis). These may cause simple redness of the affected area, vesiculation, ulceration, or abscessation. The most common causes of structural changes or sores of the oral mucosa include cold sores, mouth ulcers (aphthae), and fungal diseases such as thrush (candidiasis). Commonly occurring aphthae (about 5 to 21 percent of the total population) present as small, whitish to yellowish swellings or vesicles that cause painful inflammation of the oral mucosa and are surrounded by a reddish ring.Cold sores (fever blisters), which are often confused with aphthae, are characterized by an accumulation of painful blisters in the area of the lips that are filled with fluid. In addition, the oral mucosa can be damaged by a fungal infection with Candida albicans (candidiasis or oral thrush), which is manifested by yellow-white to reddish areas on the mucosa. In addition, changes in the oral mucosa such as leukoplakia (hyperkeratosis, white callus disease), which present as white and non-wipeable patches, may manifest. These represent the most common premalignant oral mucosal lesions and are considered precancerous lesions, as they are associated with an increased risk of manifesting squamous cell carcinoma. Chronic stimuli such as long-term nicotine use may also cause cornification disorders of the oral mucosa (leukoedema, smoker’s leukokeratosis).
