Oral Cavity

Objectives: Describe the boundaries of the oral cavity. Describe the normal anatomical structures of the oral cavity. Describe teeth and their structure. Describe the tongue and its structure. Understand the innervation of the oral cavity.

The roof of the oral cavity consists of the hard and soft palates The roof of the oral cavity consists of the hard and soft palates. The floor is formed mainly of soft tissues, which include a muscular diaphragm and the tongue. The lateral walls (cheeks) are muscular and merge anteriorly with the lips. The posterior aperture of the oral cavity is the oropharyngeal isthmus, which opens into the oral part of the pharynx. The oral cavity is separated into two regions: 1- The outer oral vestibule. 2- the inner oral cavity proper

The walls of the oral cavity are formed by the cheeks The walls of the oral cavity are formed by the cheeks. Each cheek consists of fascia and a layer of skeletal muscle sandwiched between skin externally and oral mucosa internally. The thin layer of skeletal muscle within the cheeks is principally the buccinator muscle. Buccinator muscle holds the cheeks against the alveolar arches and keeps food between the teeth when chewing.

The floor of the oral cavity proper is formed mainly by three structures: 1- A muscular diaphragm, which fills the U-shaped gap between the left and right sides of the body of the mandible and is composed of the paired mylohyoid muscles. 2- Two cord-like geniohyoid muscles above the diaphragm, which run from the mandible in front to the hyoid bone behind. 3- The tongue, which is superior to the geniohyoid muscles.

The tongue is a muscular structure that forms part of the floor of the oral cavity and part of the anterior wall of the oropharynx. The apex is directed anteriorly and sits immediately behind the incisor teeth. The root of tongue is attached to the mandible and the hyoid bone. The superior surface of the oral or anterior two-thirds of the tongue is oriented in the horizontal plane. The pharyngeal surface or posterior one-third of the tongue curves inferiorly.

The superior surface of the oral part of the tongue is covered by papillae. The inferior surface lacks papillae, but have mucosal folds. A single median fold (the frenulum of tongue) is continuous with the mucosa of the floor of the oral cavity. On each side of the frenulum is a lingual vein. The mucosa of the pharyngeal surface of the tongue is irregular because of the nodules of lymphoid tissue in the submucosa (the lingual tonsil). There are no papillae on the pharyngeal surface.

The superior surface of the oral part of the tongue is covered by papillae. The inferior surface lacks papillae, but have mucosal folds. A single median fold (the frenulum of tongue) is continuous with the mucosa of the floor of the oral cavity. On each side of the frenulum is a lingual vein. The mucosa of the pharyngeal surface of the tongue is irregular because of the nodules of lymphoid tissue in the submucosa (the lingual tonsil). There are no papillae on the pharyngeal surface.

The bulk of the tongue is composed of muscle The bulk of the tongue is composed of muscle. There are intrinsic and extrinsic lingual muscles. The intrinsic muscles of the tongue originate and insert within the substance of the tongue. They are divided into superior longitudinal, inferior longitudinal, transverse, and vertical muscles, and they alter the shape of the tongue. Working in pairs or one side at a time the intrinsic muscles of the tongue contribute to precision movements of the tongue required for speech, eating, and swallowing.

Extrinsic muscles of the tongue originate from structures outside the tongue and insert into the tongue. There are four major extrinsic muscles on each side, the genioglossus, hyoglossus, styloglossus, and palatoglossus. These muscles protrude, retract, depress, and elevate the tongue. Except for the palatoglossus, which is innervated by the vagus nerve [X], all muscles of the tongue are innervated by the hypoglossal nerve [XII].

Innervation: General sensory innervation is carried predominantly by branches of the trigeminal nerve [V]. The upper parts of the cavity, including the palate and the upper teeth, are innervated by branches of the maxillary nerve [V2]. The lower parts, including the teeth and oral part of the tongue, are innervated by branches of the mandibular nerve [V3]. Taste (special afferent-SA) from the oral part or anterior two-thirds of the tongue is carried by branches of the facial nerve [VII], which join and are distributed with branches of the trigeminal nerve [V].

Parasympathetic fibers to the glands within the oral cavity are also carried by branches of the facial nerve [VII], which are distributed with branches of the trigeminal nerve [V]. Sympathetic fibers in the oral cavity ultimately come from spinal cord level T1, synapse in the superior cervical sympathetic ganglion, and are eventually distributed to the oral cavity along branches of the trigeminal nerve [V] or directly along blood vessels.

The Teeth: The teeth are collectively called the dentition. Adults normally have 16 teeth in the mandible and 16 in the maxilla. On each side of the midline, there are two incisors, a canine,two premolars, and three molars in each jaw.

The incisors are chisel-like cutting teeth used to bite off a piece of food. The canines are more pointed and act to puncture and shred it. The premolars and molars have relatively broad surfaces adapted to crushing and grinding.

Teeth develop beneath the gums and erupt (emerge) in predictable order Teeth develop beneath the gums and erupt (emerge) in predictable order. Twenty deciduous teeth (milk teeth or baby teeth) erupt from the ages of 6 to 30 months, beginning with the incisors. Between 6 and 25 years of age, these are replaced by the 32 permanent teeth.

Human Deciduous and Permanent Teeth

Structure of Tooth

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