Buccal Mucosa Retromolar Trigone Hard Palate

Figure 5-1. Diagram of the oral cavity and subsites.

upper lip possesses two peaks forming a "cupid's bow" where the filtrum ascends to the columella of the nasal septum.

The orbicularis oris muscle receives motor innervation from the marginal and buccal branches of the facial nerve and performs a sphincteral function to maintain oral competence and to facilitate articulation of speech. This muscle has many attachments from other muscles of facial expression that elevate and depress the lips. Of clinical importance is the innervation of the depressor anguli oris muscle by the marginal mandibular branch of the facial nerve.

Sensation of the lower lip is provided by the mental nerve, the terminal segment of the alveolar branch of the mandibular division of the trigeminal nerve. The nerve exits the mental foramen of the mandible near the root of the canine tooth. Paresthesia of the chin suggests extensive mandible invasion and inferior alveolar nerve involvement by oral carcinoma.

The anterior two-thirds of the tongue is called the oral or mobile tongue and is bounded posteriorly by the V-shaped line of the circumvallate papillae. Posterior to this line is the base of tongue, which is part of the oropharynx. The oral tongue has ventral and dorsal surfaces. The mucosa of the tongue is simple stratified squamous epithelium with interspersed papillae or taste buds of four morphologies: filiform, foliate, fungiform, and circumvallate.

The tongue is comprised of intrinsic and extrinsic muscles. The intrinsic muscles are arranged in vertical and horizontal fascicles that allow the mobile tongue to change shape and consistency. There are three pairs of extrinsic muscles that provide mobility of the tongue: genioglossus, hyoglossus, and styloglossus. Protrusion of the tongue is primarily accomplished by the action of the genioglossus muscle which originates from the mandibular tubercles on the lingual surface of the arch of the mandible, and inserts diffusely into the substance of the intrinsic musculature on each side of the tongue. The motor supply to the intrinsic and extrinsic tongue muscles is the hypoglossal nerve (CN XII), which exits the skull through its own hypoglos-sal canal and courses laterally and anteriorly between the external and internal carotid arteries, immediately inferior to the occipital artery.

The sensation of the tongue is supplied by the lingual nerve, a branch of the mandibular division of the

Figure 5-1. Diagram of the oral cavity and subsites.

Figure 5-2. Distribution of oral cancers by subsite. A selected series of cases presenting to the head and neck service of Memorial Sloan-Kettering Cancer Center, New York.

trigeminal nerve (CN V3). The lingual nerve also transports parasympathetic fibers from the chorda tympani branch of the facial nerve to the sub-mandibular ganglion. The blood supply to the tongue is derived from the paired lingual arteries.

The lymphatic drainage of the tongue begins in a rich submucosal plexus, which may drain bilaterally when lesions approach the midline, the tip, or especially the base of the tongue. Tumors of the lateral mid-tongue drain predictably to the ipsilateral lymph nodes. The first echelon nodes for lesions of the tip include the submental nodes. The lateral and ventral tongue lesions metastasize to submandibular or jugulodigastric nodes while the base of tongue drains to the jugulodigastric and deep jugular nodes. Lesions of the anterior tongue may metastasize directly to the low jugular lymph nodes (level IV) of the neck.

The buccal mucosa lines the lateral oral cavity and blends with the gingiva superiorly and inferiorly and with the retromolar trigone posteriorly. The mucosa is pierced by the Stensen's duct of the parotid gland at the papilla adjacent to the second maxillary molar tooth.

The gingiva consists of thick keratinized mucosa with deep rete pegs and submucosal adherence to the periosteum. The mucosa covers the alveolar processes of the mandible and the maxilla.

The mandible possesses lingual and buccal cortices which envelop cancellous bone, dental sockets, and the mandibular canal transmitting the mandibular vessels and nerves (branch of CN V3). The mandibular surface is innervated by branches of the lingual and mental nerves while the maxillary sur face is innervated by alveolar branches of the second and third divisions of the 5th cranial (trigeminal) nerve.

The retromolar trigone is that portion of adherent keratinized mucosa covering the ascending ramus of the mandible from the third mandibular molar to the maxillary tubercle. It represents the area between the buccal mucosa laterally and the anterior tonsillar pillar medially and posteriorly. Tumors of this small region spread readily to the adjacent mandibular bone, alveolar foramen, masticator space, oropharyngeal tonsil, floor of mouth and base of tongue.

The hard palate lies within the horseshoe shape of the maxillary alveolar process. Keratinized adherent mucosa covers the palatal bone, which is divided into the primary and secondary bony palate. The primary palate consists of the palatal processes of the maxillary bones and represents the premaxilla anterior to the incisive foramen. The secondary palate is made up of the horizontal processes of the L-shaped palatine bones. On the posterior hard palate, near the maxillary second or third molar, are found the greater and lesser palatine foramina which transmit their respective vessels and nerves which are the terminal branches of the sphenopalatine vessels (branches of the internal maxillary artery) and nerves (branches of V2). Anteriorly, the midline incisive foramen near the incisors transmits the terminal branches of the nasociliary nerve and vessels to supply the primary palate region. Lymphatic drainage of the palate includes the deep jugular chain as well as the retropharyngeal nodes. Anterior lesions may metastasize to pre-vascular facial lymph nodes of the submandibular region.

The floor of the mouth is a soft thin layer of U-shaped mucosa overlying the insertion of the mylohy-oid muscle laterally, the hyoglossus muscle medially, and the insertion of the genioglossus muscle anteriorly. It covers the sublingual salivary glands, sub-mandibular (Wharton's) duct, and the lingual nerve. The blood supply is from the lingual vessels. Its lymphatic plexus is copious and drains bilaterally in the midline. The lymphatic drainage patterns include the submental and bilateral submandibular nodes, as well as the ipsilateral jugulodigastric nodes posteriorly.

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