S7 Oral Cavity - Learning Objectives
1. What are the boundaries, subdivisions and contents of the oral cavity?
The oral cavity is the area bounded:
- anteriorly by the lips,
- laterally by the cheeks,
- posteriorly by the palatoglossal arches,
- superiorly by the hard & soft palates, and
- inferiorly by the mylohyoid m.
The oral cavity can be divided into the oral cavity proper and the oral vestibule. The occlusal plane of the teeth divides these areas: oral cavity proper is internal to dental arches, and the oral vestibule is external.
The oral vestibule is a narrow space between the labii & cheeks and the teeth. The oral vestibule communicates with the external environment via the oral fissure, and is continuous with the oral cavity proper posterior to the 3rd molars.
The oral vestibule contains the:
- buccal surfaces of the teeth, alveolar processes, and associated gingivae,
- papillae & openings of the parotid (Stensen’s) ducts,
- openings of numerous minor salivary glands,
- frenulum of upper lip, and
- frenulum of lower lip.
The oral cavity proper is continuous with the oropharynx (via the oropharyngeal isthmus, the space between the palatoglossal arches). The oral cavity proper technically also contains the sublingual space, but this region is often conceptualized separately.
The oral cavity proper (exclusive of the sublingual space) contains the:
- lingual surfaces of teeth, alveolar processes, and associated gingivae,
- tongue (body),
- lingual frenulum
- sublingual caruncles & openings of the submandibular (Wharton’s) ducts,
- sublingual folds & openings of the sublingual ducts, and
- openings of numerous minor salivary glands.
2. What are the contents and relationships of the sublingual space?
The sublingual (fascial) space is the area between the mucosa of the floor of the oral cavity proper and the mylohyoid m. Posterior to the margin of the mylohyoid m., the sublingual space is continuous with the submandibular fascial space (inferiorly) and lateral pharyngeal fascial space (posteriorly). Infections (mandibular odontogenic, or other) may spread from the sublingual space to adjacent spaces (submandibular, lateral pharyngeal, retropharyngeal, and beyond). Cellulitis (and related edema) in the sublingual, submandibular, and sometimes also the submental spaces may endanger the airway and require immediate intervention. This is known as Ludwig’s angina, and it is life-threatening.
The sublingual space contains:
- sublingual glands (& associated ducts),
- submandibular ducts,
- lingual aa. (& brs.),
- lingual vv. (& tributaries),
- lingual nn. (& associated submandibular ganglia)
- hypoglossal nn. (& vena comitantes)
- deep lobe of submandibular gland.
Of the three types of major salivary glands, the sublingual glands are the smallest. They are located superior to the mylohyoid m. and when covered with mucosa, form the sublingual folds. These glands drain via numerous small ducts along the sublingual folds. The deep, smaller part of the submandibular gland is also located in this area and is closely associated with the posterior end of the sublingual gland.
The mylohyoid line of the mandible is formed by the attachment of the mylohyoid m. The two salivary glands in this region are associated with this line: sublingual gland superior, and submandibular gland inferior.
The lingual a. is typically the second branch of the external carotid a. that leaves the external carotid anteriorly. Passing between the hyoglossus m. and the middle pharyngeal constrictor m., the lingual a. supplies the floor of the oral cavity and the tongue. The lingual a. produces several branches, chiefly:
- Dorsal lingual brs. - arise medially to the hyoglossus m.; supplies the posterior tongue, soft palate, and palatine tonsil,
- Sublingual a. - arise anteriorly to the hyoglossus m.; supplies the sublingual gland, and muscles and tissues of the floor of the oral cavity, and
- Deep lingual a. - the terminal br. of the lingual a. - lies along the inferior margin to the tip of the tongue; supplies the anterior tongue.
Nearly all of the lingual a. branches anastomose with their contralateral paired artery along the midline.
Deep to the mucosa in the oral cavity proper, the lingual n. and submandibular duct cross. The lingual n. descends into the oral cavity and loops under (‘cradles’) the submandibular duct to provide general sensory innervation to the anterior 2/3rds of the tongue.
The submandibular (Wharton’s) duct traverses the space between the submandibular gland and sublingual caruncle. The duct is located between the hypoglossal n. and lingual n. in association with the hyoglossus m. The lingual n. passes deep to the duct about midway in the oral cavity.
The lingual n. is an afferent branch of the posterior trunk of V3. It traverses the infratemporal fossa medial to the inferior alveolar n., where it is joined by the chorda tympani (branch of facial n., CN VII). Chorda tympani carries presynaptic parasympathetic fibers to the submandibular gland and taste to the body of the tongue (excluding the vallate papillae). The lingual n. enters the oral cavity superior to the mylohyoid m., and enters the tongue to provide sensory innervation to the body of the tongue and the floor of the oral cavity.
The submandibular ganglion is delicately associated with the lingual n. and is superior to the deep portion of the submandibular gland. This ganglion is one of four named peripheral parasympathetic ganglia (ciliary, pterygopalatine, submandibular, and otic). The submandibular ganglion receives preganglionic parasympathetic fibers from the chorda tympani, a branch of the facial n. (CN VII). Postganglionic parasympathetic fibers leave the ganglion to innervate the submandibular and sublingual glands, among other smaller glands (e.g. anterior lingual) by means of the lingual n., a branch of V3.
The vena comitans of hypoglossal n. is a tributary of the lingual v. This vein accompanies the hypoglossal n. (CN XII) inferiorly along the hyoglossus m.
3. Describe the innervation of the following: cheeks, teeth, and gingivae.
Cheeks (skin, buccinator m., and mucosa) are afferently innervated by the (long) buccal nn. (V3).
Teeth are innervated by alveolar nn. Maxillary teeth are innervated by superior alveolar nn. The superior dental plexus is composed of contributions from the superior alveolar brs. Posterior superior alveolar (PSA) brs. come directly from the maxillary n. (V2) in the pterygopalatine fossa. These branches descend deep to the mucosa of the maxillary sinus and afferently serve the maxillary molars. The middle superior alveolar brs. come from the infra-orbital n., and afferently innervate portions of the maxillary sinus and maxillary premolar teeth. The middle superior alveolar (MSA) brs. are frequently absent. Anterior superior alveolar (ASA) brs. also come from the infra-orbital n., and afferently serve the maxillary incisors and canines. Mandibular teeth are innervated by the inferior alveolar n. (IAN) and its brs.
Gingivae (gums) of the maxillary dental arch are innervated by brs. of V2, whereas gingivae of the mandibular dental arch are innervated by brs. of V3. See tables below for a summary.
4. Name the intrinsic and extrinsic muscles of the tongue and their origins, insertions and innervation.
Intrinsic tongue muscles: There are four types of intrinsic muscles of the tongue:
- superior longitudinal,
- inferior longitudinal,
- transverse, and
Intrinsic tongue muscles independently (and in unison) alter tongue shape and perform smaller, more precise movements. Intrinsic tongue mm. are innervated by the hypoglossal n. (CN XII).
Extrinsic tongue muscles: Extrinsic tongue muscles attach elements of the tongue to the skull and hyoid bone to affect gross movements of the tongue. Extrinsic tongue muscles are innervated by the hypoglossal n. (CN XII).
5. Describe the regions of the tongue, and the nerves and modalities serving these regions.
The tongue has dorsal (superior) and ventral (inferior) surfaces.
The dorsal (superior) surface of the tongue is divided by paired terminal sulci into the body (presulcal/oral part) and root (postsulcal/pharyngeal part). A median sulcus runs superficial to a fibrous septum which runs the full length of the tongue, but the median sulcus ends in convergence with the terminal sulci. Where the three sulci converge is an indentation called the foramen caecum, an embryonic remnant of the thyroid diverticulum and thyroglossal duct. An outline of the three sulci resembles an arrow, pointing towards the root of the tongue and beyond. Just anterior to the inverted ‘V’ of the terminal sulci are two rows of vallate papillae, each running parallel to its adjacent terminal sulcus. The lateral end of each terminal sulcus extends to the palatoglossal arch. Thus, the body of the tongue rests roughly in the oral cavity proper, whereas the root of the tongue rests in the oropharynx. The root of the tongue extends from the terminal sulci (and associated palatoglossal arches) posteriorly to the epiglottic valleculae, where it is attached to the epiglottis via three folds: a median glosso-epiglottic fold (which separates the valleculae) and paired lateral glosso-epiglottic folds. The root of the tongue is devoid of papillae, but has a rugosa appearance due to submucosal collections of lymphatic nodules, collectively known as the lingual tonsil.
The ventral surface of the tongue is connected to the mucosa of the floor of the oral cavity via the lingual frenulum. It may be highly variable in size and attachment. In some individuals a shortened and thickened lingual frenulum may limit the mobility of the tongue, a condition known as ankyloglossia (‘tongue-tie’). Ablation of the lingual frenulum (frenulotomy) is less frequently performed to aid in difficulties with speech, but it may increase success of latching for breast feeding.
Sublingual folds laterally flank the lingual frenulum, and are formed by the sublingual glands and ducts of the submandibular glands shaping the mucosa. Along these folds are the bilateral openings of the sublingual ducts.
The sublingual caruncle is situated at the confluence of the sublingual folds and the lingual frenulum. The sublingual caruncle is the location where the submandibular (Wharton’s) ducts secrete saliva into the oral cavity proper.
Fimbriated folds flank the lingual frenulum on the ventral surface of the tongue. Typically, the lingual veins are visible deep to the inferior surface mucosa between the lingual frenulum and the fimbriated folds.
With the exception of the palatoglossal m. (vagus n.), the tongue is efferently innervated entirely by the hypoglossal n. (CN XII).
Afferently, the tongue has both general somatic and special visceral (taste) afferent innervations. An important landmark for the afferent innervation of the tongue are the vallate papilla (not the terminal sulci). In terms of somatic afferents:
- areas anterior to the vallate papillae are innervated by the lingual n. (V3), whereas
- areas posterior to the vallate papillae are innervated by the glossopharyngeal n.
There is a slight overlap of somatic afferent innervation in the posteromedial root of the tongue, which is innervated by both the glossopharyngeal n. and vagus n (via the internal br. of the superior laryngeal n.). The vallate papillae also demarcate the two sources of special visceral afferent (taste) serving the taste buds:
- anterior to the vallate papillae, taste is modulated via the facial n. (chorda tympani ← lingual n.), whereas
- posterior to the vallate papillae, taste is modulated via the glossopharyngeal n.
6. Describe the various papillae of the tongue.
The lingual papillae consist of four types (from anterior to posterior):
- Filiform papillae are small, conical eruptions covering the dorsal anterior two-thirds of the tongue. Filiform papillae are not associated with taste buds, but rather are important for the tactile sensation and manipulation of food items.
- Fungiform papillae are moderately sized, mushroom-shaped eruptions interspersed throughout the filiform papillae. Fungiform papillae host taste buds innervated by the axons from chorda tympani (facial n.) by way of the lingual n. (V3).
- Foliate papillae are found in trenches on the lateral margins of the tongue. Taste buds associated with foliate papillae are in greatest density during childhood, and often diminish with age.
- Vallate papillae (sometimes referred to as circumvallate papillae) are located on the posteriormost border of the oral part of the dorsal tongue, just anterior to the terminal sulci and foramen caecum. These papillae are the largest of the lingual papillae. Vallate papillae host taste buds innervated by the axons from the glossopharyngeal n. (CN IX), even though they lie on the presulcal side of the tongue.