Oral mucosa
I-INTRODUCTION:
Anatomically the oral cavity or buccal cavity ( cavum oris ), is a roughly quadrangular, symmetrical cavity; located in the lower part of the face.
It is open to the front and back, limited in front by the lips, laterally by the cheeks, above by the palate and below by the tongue and the sublingual region (floor of the mouth), behind by the isthmus of the throat, which makes it communicate with the pharynx. The oral cavity is occupied by the dental arches and the tongue.
- The oral cavity presents to be described:
- The oral and pharyngeal mucosa;
- The lingual mucosa;
- The salivary glands;
- The teeth.
II-THE ORAL MUCOSA:
1-DEFINITION:
It is a richly vascularized and innervated membrane, which lines the inner wall of the lips, cheeks, hard palate, soft palate, floor of the mouth and the lower part of the dental arches (vestibules and alveolar mucosa). It constantly secretes a moistening substance called mucus .
2-ANATOMY:
It is in continuity:
– Forward with the skin tissue of the face formed by the external slope of the lips
-Behind with the oropharyngeal mucosa (soft palate and tonsils)
– Laterally, with the internal covering of the cheeks;
-At the top, with the ceiling of the oral cavity delimiting the hard palate;
-At the bottom, with the floor of the mouth that it covers and the base of the tongue.
3-HISTOLOGY:
The oral mucosa is made up of:
- Malpighian epithelium: squamous and multi-stratified specialized keratinized or not depending on its location:
- Keratinized at the level of the masticatory mucosa (gum and hard palate);
- Non-keratinized over most of the oral cavity (lips, cheeks, soft palate, floor
- Connective tissue (lamina propria or chorion):
-Superficial or papillary zone: it is made up of loose connective tissue, with papillae and nerve endings. The epithelial ridges and the connective papillae have a weak appearance which does not allow good anchoring in the connective tissue (reflecting the flexibility of these mucous membranes).
-Deep zone or dermis: made of dense connective tissue rich in fibers, there are fatty pellets ,
- The basement membrane : Between the epithelium and the connective tissue, it measures 1 to 2 µm thick (depending on its appearance under electron microscopy, several structures called lamina densa and lamina lucida are delineated, as well as anchoring fibrils.
- Submucosa: The chorion rests on a submucosa, which is a layer of fat (adipose tissue) where the majority of salivary glands, vessels and nerves are located, separates the mucosa from the underlying bone or muscles. It is found only at the level of the labial, jugal, soft palate and floor mucosa.
3-1 The alveolar mucosa:
A- Anatomy:
1-The oral vestibule: (vestibulum oris)
The vestibule is a virtual space delimited apically by the deflection zone between the alveolar mucosa and the labial and jugal mucosa and coronally by the external face of the keratinized gingiva.
Depending on the extent of these various components, very variable vestibule depths can be described.
At its level, folds connect the jugal and labial mucosa to the alveolar processes (upper labial frenum and lower labial frenum as well as flanges).
2-The alveolar mucosa:
The alveolar mucosa is distinguished from the gingiva by its redder color, its smoother appearance and its mobility relative to the underlying planes. It is continuous with the keratinized gingiva after the mucogingival line in the apical direction.
Means of localization of the muco-gingival line:
- Inspection
- The pressure
- Traction
- ROLLER test
B-Histology of the alveolar mucosa:
A non-keratinized epithelium whose thickness varies between 0.005 and 0.3 mm, and which is thicker than the epithelium of the floor of the mouth (260±40 µm).
A connective tissue rich in elastic fibers; the connective papillae are conical, about 100 µm long, they measure 25 µm at their base, they often have bifurcations and angulations; there are 46 papillae.
3-2 The labial mucosa:
The lips are mobile muscular and membranous folds, limiting the oral orifice. They have four planes which are from the outside to the inside:
-The skin
-The muscle layer
-The submucosal (glandular) layer
-The mucosa: It lines the orbicularis, laterally continues with the oral mucosa, this mucosa is flexible, elastic which allows its mobilization.
They have an anterior or cutaneous face (white lip), a posterior or mucous face and a free cutaneous-mucous edge (red or vermilion lip or KLEIN zone). The ends joined together form the labial commissures, constitute the angles of the mouth.
-Histology of the labial mucosa:
1-The skin surface is covered with a keratinized stratified squamous epithelium, the dermis contains numerous hair follicles, sebaceous glands, sweat glands and sensory receptors.
2-The mucous surface :
It consists of a non-keratinized stratified squamous epithelium, it is thicker and has neither a horny nor a granular layer, it rests on a loose chorion which contains salivary glands and a submucosa. The transition from the white lip to the mucosa occurs at the level of a special zone, “the red lip” or vermilion (KLEIN zone), corresponding to the thin and transparent epidermis, little keratinized. At this level, hair formations and sebaceous glands have disappeared.
3-3 The palatine mucosa:
The anterior 2/3 form the hard palate which is made up of a bony plate.
The posterior third forms the soft palate or velum, which is a continuation of the hard palate. On the posterior edge is the uvula, which, when the palate is relaxed, rests on the tongue.
From the uvula, 2 membranous pillars depart. Between the two, and on each side are the tonsils.
The soft palate plays an important role during swallowing, as it presses against the wall of the pharynx, thus isolating the airway from the digestive tract.
Histology of the palatine mucosa:
At the level of the bony palate, the mucosa is pink in color, adheres strongly to the periosteum and is made up of a keratinized stratified squamous epithelium.
At the level of the veil, the nonkeratinized epithelium rests on a thicker chorion and covers striated muscle fibers and numerous accessory mucous-type salivary glands.
The uvula has a striated muscular axis and loose connective tissue covered by a buccal-type ( non-keratinized) epithelium . Taste buds are described within this palatine mucosa.
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