The oral or mouth cavity is divided into
- an outer, smaller portion, the vestibule, and
- an inner larger part, the oral cavity proper.
Vestibule
The vestibule of the mouth is a narrow space bounded externally by the lips and cheeks, and internally, by the teeth and gums.
It communicates:
a. With the exterior through the oral fissure.
b. With the mouth open it communicates freely with the oral cavity proper.
Even when the teeth are occluded a small communication remains behind the third molar tooth.
The parotid duct opens on the inner surface of the cheek opposite the crown of the upper second molar
tooth.
Numerous labial and buccal glands (mucous) situated in the submucosa of the lips and cheeks open into the vestibule.
Four or five molar glands (mucous), situated on the buccopharyngeal fascia also open into the vestibule.
Except for the teeth, the entire vestibule is lined by mucous membrane.
The mucous membrane forms median folds that pass from the lips to the gums, and are called the frenula of the lips.
Clinical Anatomy
The papilla of the parotid duct in the vestibule of the mouth provides access to the parotid duct for the injection of the radiopaque dye to locate calculi in the duct system or the gland.
Koplik's spots are seen as white pin point spots around the opening of the parotid duct in measles. These are diagnostic of the disease.
Lips
The lips are fleshy folds lined externally by skin and internally by mucous membrane.
The mucocutaneous junction lines the 'edge' of the lip, part of the mucosal surface is also normally
seen.
Each lip is composed of:
a. Skin.
b. Superficial fascia.
c. The orbicularis oris muscle.
d. The submucosa, containing mucous labial glands and blood vessels.
e. Mucous membrane.
The lips bound the oral fissure.
They meet laterally at the angles of the mouth.
The inner surface of each lip is supported by a frenulum which ties it to the gum.
The outer surface of the upper lip presents a median vertical groove, the philtrum.
Lymphatics of the central part of the lower lip drain to the submental nodes; the lymphatics from the rest
of the lower lip pass to the submandibular nodes.
Cheek
The cheeks are fleshy flaps, forming a large part of each side of the face.
They are continuous in front with the lips, and the junction is indicated by the nasolabial sulcus (furrow) which extends from the side of the nose to the angle of the mouth.
Each cheek is composed of:
a. Skin.
b. Superficial fascia containing some facial muscles, the parotid duct, mucous molar glands, vessels and nerves.
c. The buccinator covered by buccopharyrgeal fascia and pierced by the parotid duct.
d. Submucosa, with mucous buccal glands.
e. Mucous membrane.
The buccal pad of fat is best developed in infants.
It lies on the buccinator partly deep to the masseter and partly in front of it.
The lymphatics of the cheek drain chiefly into the submandibular and preauricular nodes, and partly also to the buccal and mandibular nodes.
Oral Cavity Proper
It is bounded
anterolaterally by the teeth, the gums and the alveolar arches of the jaws.
The roof is formed by the hard palate and the soft palate.
The floor is occupied by the tongue posteriorly, and presents the sublingual region anteriorly, below the tip of the tongue.
Posteriorly, the cavity communicates with the pharynx through the oropharyngeal isthmus (isthmus of fauces) which is bounded superiorly by the soft palate, inferiorly by the tongue, and on each side by the palatoglossal arches.
The sublingual region presents the following features'
a. In the median plane, there is a fold of mucosa passing from the inferior aspect of the tongue to the floor of the mouth. This is the frenulum of the tongue.
b. On each side of the frenulum, there is a sublingual papilla.
On the summit of this papilla, there is the opening of submandibular duct.
c. Running laterally and backwards from the sublingual papilla, there is the sublingual fold which overlies the sublingual gland.
A few sublingual ducts open on the edge of this fold.
Lymphatics from the anterior part of the floor of the mouth pass to the submental nodes.
Those from the hard palate and soft palate pass to the retropharyngeal and upper deep cervical nodes.
The gums and the rest of the floor drain into the submandibular nodes.
Gums/ gingivae
The gums are the soft tissues which envelop the alveolar processes of upper and lower jaws and surrounds the neck of the teeth.
These are composed of dense fibrous tissue covered by stratified squamous epithelium.
Each gum has two parts:
a. The free part surrounds the neck of the tooth like a collar.
b. The attached part is firmly fixed to the alveolar arch of the jaw.
The fibrous tissue of the gum is continuous with the periosteum lining the alveoli (periodontal membrane).
Nerve Supply:
Upper Gums
Labial side - posterior, middle and anterior superior alveolar nerves
Lingual side - Anterior palatine and nasopalatine nerves from pterygopalatine ganglion
Lower Gums
Labial side - buccal branch of Mandibular nerve and incisive branch of mental nerve
Lingual side - lingual nerve
Lymphatics of the upper gums pass to the submandibular nodes.
The anterior part of the lower gums drains into the submental nodes, whereas the posterior part drains into the submandibular nodes.
Teeth
The teeth form part of the masticatory apparatus and are fixed to the jaws.
In man, the teeth are replaced only once (diphyodont) in contrast with non-mammalian vertebrates where teeth are constantly replaced throughout life (polyphyodont).
The teeth of the first set (dentition) are known as milk, or deciduous teeth, and the second set, as permanent teeth.
The deciduous teeth are 20 in number.
In each half of each jaw, there are two incisors, one canine, and two molars.
The permanent teeth are 32 in number, and consist of two incisors, one canine, two premolars and three molars in each half of each jaw
Parts of a tooth
Each tooth has three parts:
1. A crown, projecting above or below the gum.
2. A root, embedded in the jaw beneath the gum.
3. A neck, between the crown and root and surrounded by the gum
Structure
Structurally, each tooth is composed of:
1 The pulp in the centre
2 The dentine surrounding the pulp.
3 The enamel covering the projecting part of dentine, or crown.
4 The cementum surrounding the embedded part of the dentine.
5 The periodontal membrane.
The pulp is loose fibrous tissue containing vessels, nerves and
lymphatics, all of which enter the pulp cavity through the apical foramen.
The pulp is covered by a layer of tall columnar cells, known as
odontoblasts which are capable of replacing dentine any time in life.
The dentine is a calcified material containing spiral tubules radiating
from the pulp cavity.
Each tubule is occupied by a protoplasmic process from one of the
odontoblasts.
The calcium and organic matter are in the same proportion as in bone.
The enamel is the hardest substance in the body.
It is made up of crystalline prisms lying roughly at right angles to the surface of the tooth.
The cementum resembles bone in structure, but like enamel and dentine
it has no blood supply, nor any nerve supply.
Over the neck, the cementum commonly overlaps the cervical end of enamel; or, less commonly, it may just meet the enamel.
Rarely, it stops short of the enamel (10%) leaving the cervical dentine covered only by gum.
The periodontal membrane (ligament) holds the root in its socket.
This membrane acts as a periosteum to both the cementum as well as the
bony socket.
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