Introduction
The oral cavity is not only the first part of the digestive tract but also a mirror to general health and aids in the act of respiration. It is adapted to receive food (ingestion) and break it down into small pieces with the help of our teeth (mastication) for easy swallowing. It also helps in speech. The teeth and jaw structure aids in providing muscle tone and beauty to the face.
How Does the Oral Cavity Develop?
The development of the oral cavity takes place in the six to eight weeks of fetal development. The development starts around the fourth week. A set of six pharyngeal arches are formed.
Each arch gives rise to different parts of the oral cavity.
What Are the Different Parts of the Oral Cavity?
The mouth is mainly divided into two parts - the oral cavity proper and the vestibule.
Oral Cavity Proper - It is the larger part of the oral cavity. It is largely occupied by the tongue posteriorly. The oral cavity communicates posteriorly with the pharynx through the oropharyngeal isthmus, also called the isthmus of fauces, which is bounded superiorly by the soft palate, inferiorly by the tongue, and laterally by palatoglossal arches. Palatoglossal arches are folds of mucus membrane running vertically down from each side of the soft palate to the corresponding lateral aspect of the tongue.
The Oral Vestibule - It is the narrow space that is outside the zone of the gingiva or gums and the rendition of the teeth structures; however, bound by the lips and oral mucosal membrane of the cheeks. When the mouth is open, it communicates with the oral cavity proper, but when the mouth is closed, that is when the teeth are occluded, it communicates with the oral cavity through a small gap behind the third molar tooth. The vestibule is lined by mucous membrane except in the area of teeth. The parotid duct opens into the lateral wall of the vestibule opposite the crown of the upper second molar tooth, openings of four to five molar glands (mucous) situated on the buccopharyngeal fascia and openings of labial and buccal mucous glands are also present.
Lips - They are a pair of mobile musculo-fibrous folds that surround the opening of the mouth. Upper and lower lips meet laterally on each side at an angle called the angle of mouth. The lips are lined externally by the skin and internally by the mucous membrane. The mucocutaneous junction lies at the edge of the mucosal surface and is normally visible. The center of the upper lip presents with a depression known as philtrum, which is limited by ridges of the skin. The internal aspect of each lip is connected to the corresponding gum by a median fold of the mucous membrane called the frenulum of the lip.
Structure - Each lip is largely composed of the orbicularis oris muscle. In addition, it contains labial (mucous) glands and blood vessels. It is lined externally by skin which contains sweat glands and sebaceous glands with hair follicles (the hairs are thicker and more numerous in adult males). They are lined internally with the mucus membrane. The mucocutaneous junction of the lip is lined by thin keratinized stratified squamous epithelium overlying a highly vascular dermis which is responsible for the color. It does not have any hair.
The lymphatic drainage of the lips drains into the submandibular lymph node, which drains the upper lip and lateral halves of the lower lip, the submental lymph nodes, and the center portion of the lower lip.
Nerve Supply - The skin of lips is innervated by branches of the infraorbital nerve (upper lip) and mandibular nerve (lower lip). Muscles are supplied by the facial nerve.
Cheeks - The cheek is largely composed of the buccinator muscle. In addition, it also contains buccal glands, blood vessels, and nerves. The buccinator muscle overlies the buccal pad of fat (best developed in infants) and is internally lined by buccopharyngeal fascia. Layers of the cheek from superficial to deep skin, superficial fascia containing muscles of facial expression, buccinators muscle, the buccal pad of fat, buccopharyngeal fascia, submucosa, containing buccal (mucous) glands, and mucous membrane. The last five layers of the cheek are pierced by the parotid duct. The lymphatic drainage from the cheek is directed through the submandibular and preauricular lymph nodes.
Nerve Supply - The skin of the cheek is innervated by zygomaticofacial as well as the infraorbital branch of the maxillary nerve. The oral mucus membrane of the cheek, in turn, is supplied by the buccal branch of the mandibular nerve. The cheek muscles are supplied by the facial nerve.
Teeth - The teeth are embedded in the alveoli or sockets of the alveolar ridges of the mandible and the maxilla. Each individual has two sets of dentitions, the temporary or deciduous teeth and the permanent teeth.
Structure - Although the shapes of the different teeth vary, the essential structure is the same and consists of:
- Crown - It is the part that protrudes from the gum.
- Root - It is the part embedded in the bone.
The neck is the slightly narrowed region where the crown merges with the root. Blood vessels and nerves pass to the tooth through a small foramen at the apex of each root. Of the four main parts or structures of the tooth, the first layer is the calcified hard enamel layer that protects the second layer - dentin. Dentin is a living tissue that contains tubular structures called dentinal tubules sensitive to heat and cold and directly communicative with the nerve structure of the tooth. The third layer or to simply put it as the nerve layer is the pulp tissue of the tooth also called the root canals that contain the individual tooth nerves penetrating it. This tissue also has rich vasculature comprising blood vessels and connective tissue.
The root of the tooth outwardly has the cementum layer, which is a hard tissue that anchors the soft tissue periodontal ligament fibers for support and anchorage of the tooth to the bone.
The arterial supply of upper teeth is supplied by posterior superior, middle superior, and anterior superior alveolar arteries, which are branches from the maxillary artery. The lower teeth are supplied by the inferior alveolar artery, a branch of the maxillary artery. The nerve supply of upper teeth is by the superior dental plexus of nerves formed by posterior superior, middle superior, and anterior superior alveolar nerves. These are branches of the maxillary division of the fifth cranial nerve or the trigeminal nerve. The lower teeth of the mandible are supplied by the inferior alveolar nerve or dental nerve, a branch of the posterior division of the mandibular division of the fifth cranial nerve.
Palate - This is the roof of the mouth that makes a clear distinction between the nasal and the oral cavity. The hard palate is composed of the bony structure and is fixed, while the soft palate is comprised of muscle fibers and is covered by the soft mucous membrane.
What Are the Muscles Present in the Oral Cavity?
The muscles present in the oral cavity are as follows:
- The floor of the oral cavity is made of mylohyoid and geniohyoid muscles.
- The superior border of the oral cavity is the soft palate and is made up of five muscles:-
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- Tensor veli palatini.
- Musculus uvulae.
- Levator veli palatini.
- Palatopharyngeus.
- Palatoglossus.
What Are the Main Functions of the Oral Cavity?
The main functions of the oral cavity include;
- Formation of speech.
- Helps in chewing.
- Intake and digestion of food.
- Respiration.
- Helps in the perception of taste.
- Provide beauty to the face and means for facial expression.
Conclusion:
Thus, it is important to understand the significance of our human oral cavity as it is a link to general systemic health because of its functions. The rich neurovascular and arterial supply makes the mouth a complex voluntary organ essential for maintaining facial form, tone, and quality of life.
