Chapter 51: The mouth tongue and teeth
The mouth is lined by stratified squamous epithelium, from which oral smears may be taken for chromosomal studies. The temperature in the mouth is about 37 degrees C. (98.6 degrees F). Mouth-to-mouth and mouth-to-nose are important methods of artificial respiration. The oral cavity consists of two portions, the vestibule and the oral cavity proper.
The vestibule is the cleft between the lips and cheeks externally and the gums and teeth internally. The parotid duct opens opposite the upper second molar. When the teeth are in contact, the vestibule and oral cavity proper communicate only by a gap between the last molars and the ramus of the mandible.
The oral cavity proper (fig. 51-1) is bounded by the alveolar arches, teeth and gums, and palate and tongue. It communicates posteriorly with the oropharynx by an opening termed the faucial isthmus, between the palatoglossal arches. The inferior surface of the tongue is connected to the floor of the mouth by a median fold of mucous membrane, the frenulum (fig. 51-1B). The submandibular duct opens on an elevation, the sublingual papilla, on the sides of the frenulum. Laterally, the sublingual fold, which is produced by the sublingual gland, contains the openings of the sublingual ducts.
The lips are musculofibrous folds that are connected to the gums by superior and inferior frenula. The median part of the upper lip shows a shallow external groove, the philtrum. The lips consist (from external to internal) chiefly of skin, the orbicularis oris muscle, labial glands, and mucosa. Cleft lip is most frequent in the upper lip in a paramedian position, and it is often associated with cleft palate. The cheeks, which contain the buccinator muscle and buccal glands, resemble the lips in structure.
The palate is the roof of the mouth and the floor of the nasal cavity. It extends posteriorward into the pharynx (see fig. 53-4). The palate has "an extravagant arterial supply" (from branches of the maxillary artery) and many sensory nerves (branches of the pterygopalatine ganglion). The palate comprises the hard palate, or anterior two thirds, and the soft palate, or posterior third.
The hard palate contains the bony palate, formed by the palatine processes of the maxillae and the horizontal plates of the palatine bones (see fig. 52-2). The mucoperiosteum of the hard palate contains many palatine glands, a median raphe, and transverse palatine folds or rugae.
The soft palate (velum palatinum) is a mobile, fibromuscular fold suspended from the hard palate posteriorly and ending in the uvula. It separates partially the nasopharynx and oropharynx and aids in closing the pharyngeal isthmus in swallowing and speech. The soft palate is continuous laterally with two folds, the palatoglossal and palatopharyngeal arches.
The muscles of the soft palate are listed in table 51-1.
The palatine aponeurosis is an expansion of the anterior part of the
palate to which the muscles of the palate are attached. With the
exception of the tensor, all the muscles of the palate are thought to
be innervated through the pharyngeal plexus by the internal branch of
accessory nerve, a nerve that actually courses with the vagus nerve in
humans. Other possible contributions are from cranial
nerves VII, IX, and XII. The muscles aid in closing the oral cavity
the pharyngeal cavity and the oropharynx from the nasopharynx. They
take part in phonation and swallowing. The tensor is perhaps
responsible for opening the auditory tube, leading to the "popping" in
the ears when swallowing. The sensory innervation of the soft palate is
from the lesser palatine nerve (a branch of the maxillary division of
The tongue (L., lingua; Gk, glossa), situated in the floor of the mouth, is attached by muscles to the hyoid bone, mandible, styloid processes, and pharynx. The tongue is important in taste, mastication, swallowing, and speech. It is composed chiefly of skeletal muscle, is partly covered by mucous membrane, and presents a tip and margin, dorsum, inferior surface, and root (fig. 51-2B and C). The tip, or apex, usually rests against the incisors and continues on each side into the margin.
The dorsum (fig. 51-2A) extends from the oral cavity into the oropharynx. A V-shaped groove, the sulcus terminalis, runs laterally and anteriorward from a small pit, the foramen cecum. The sulcus terminal is is the boundary between (1) the oral part, or anterior two thirds, and (2) the pharyngeal part, or posterior third, of the tongue. The foramen cecum, when present, indicates the site of origin of the embryonic thyroglossal duct.
The oral part of the dorsum may show a shallow median groove. The mucosa has numerous minute lingual papillae: (1) the filiform papillae, the narrowest and most numerous; (2) the fungiform papillae, with rounded heads and containing taste buds; (3) the vallate papillae, about a dozen large projections arranged in a V-shaped row in front of the sulcus terminalis and containing numerous taste buds; and (4) the folia, inconstant grooves and ridges at the margin posteriorly.
The pharyngeal part of the dorsum faces posteriorly. The base of the tongue forms the anterior wall of the oropharynx and can be inspected by downward pressure on the tongue with a spatula or by a mirror. Lymphatic follicles in the submucosa are collectively known as the lingual tonsil. The mucosa is reflected onto the anterior aspect of the epiglottis (median glossoepiglottic fold) and onto the lateral wall of the pharynx (lateral glosso-epiglottic fold). The depression on each side of the median glosso-epiglottic fold is termed the vallecula.
The inferior surface of the tongue (see fig. 51-1B) is connected to the floor of the mouth by the frenulum, lateral to which the deep lingual vein can be seen through the mucosa. Lateral to the vein is a fringed fold, the plica fimbriata. The tongue contains a number of lingual glands.
The root of the tongue rests on the floor of the mouth and is attached to the mandible and hyoid bone. The nerves, vessels, and extrinsic muscles enter or leave the tongue through its root.
All the muscles are bilateral, being partially separated by a median septum. Intrinsic muscles are arranged in several planes. The chief extrinsic muscles (fig. 51-3) are listed in table 51-2. The genioglossus is a vertically placed fan-shaped muscle that is in contact with its fellow medially. The attachment of the genioglossi to the mandible prevents the tongue from falling backward and obstructing respiration. Anesthetists keep the tongue forward by pulling the mandible forward. The hyoglossus, flat and quadrilateral, is largely concealed by the mylohyoid muscle. The glossopharyngeal nerve, stylohyoid ligament, and lingual artery pass deep to the posterior border of the hyoglossus (see fig. 49-2). With the exception of the palatoglossus, all the muscles of the tongue are supplied by the hypoglossal nerve.
The main artery is the lingual artery (fig. 49-4), a branch of the external carotid. It is accompanied by lingual veins. The deep lingual vein (or ranine vein) can be seen in the floor of the mouth at the side of the frenulum. The various veins of the tongue drain ultimately into the internal jugular.
The lymphatic drainage is important in the early spread of carcinoma of the tongue. The drainage is to the submental, submandibular, and deep cervical nodes (fig. 51-4), and extensive communications occur across the median plane.
Sensory innervation (see fig. 51-2A).
The anterior two thirds of the tongue is supplied by (1) the lingual nerve (of the mandibular nerve) for general sensation and by (2) the chorda tympani (a branch of the facial nerve that runs in the lingual nerve) for taste. The posterior third of the tongue and the vallate papillae are supplied by the glossopharyngeal nerve for both general sensation and taste. The nerves for taste are cranial nerves VII, IX, and X. The internal branch of the vagus is responsible for general sensation and taste near the epiglottis.
Teeth (table 51-3)
Each tooth (Gk, odous, odontos; L., dens, dentis) is composed of connective tissue, the pulp, covered by three calcified tissues: dentin(e), enamel, and cement(um). The pulp occupies the pulp cavity, which comprises a pulp chamber in the crown and one or more root canals in the root(s). The root canals open by apical foramina, which transmit nerves and vessels to the pulp. Enamel is highly radioopaque (see fig. 51-10). The cement is connected to the alveolar bone by periodontium to form a fibrous joint between a tooth and its socket (alveolus). The gums (gingivae) are composed of dense fibrous tissue covered by oral mucosa.
The anatomical crown of a tooth is the part covered by enamel, whereas the clinical crown is the part that projects into the oral cavity (fig. 51-5). The root is covered by cement and includes the neck, adjacent to the crown. Some teeth have two or three roots.
The teeth are classified as incisors, canines, premolars, and molars. The eight incisors cut food by their edges. The four canines ("cuspids" or "eye-teeth") assist in cutting. The eight premolars ("bicuspids") assist in crushing food. They replace the deciduous molars. The twelve molars crush and grind food. The roots of the upper molars are closely related to the floor of the maxillary sinus. Hence pulpal infection may cause sinusitis, or sinusitis may cause toothache. The third molar ("wisdom tooth") is highly variable.
Most of the teeth in an adult are successional, i.e., they succeed a corresponding number of deciduous teeth ("milk teeth"). The permanent molars, however, are accessional, i.e., they are added behind the milk teeth during development.
No functioning teeth have penetrated the oral cavity (i.e., erupted) at birth. The "milk teeth" appear in the oral cavity between the ages of 6 months and 2.5 years. The first teeth to erupt are the lower medial incisors, at about 6 months. All of the deciduous teeth have been shed by about 12 years. According to the Universal System for nomenclature of teeth, the 20 deciduous teeth are lettered beginning with the patient's right upper second molar tooth ("A") and proceeding across the upper jaw to the left upper second molar ("J"). The lettering system thence proceedes to the left lower second molar ("H") and then across the lower jaw from left to right to the right lower second molar ("T").
The so-called permanent teeth begin to appear in the oral cavity at the age of about 6 years, and they have replaced the deciduous teeth by about 12 years. The first to erupt is the first molar, at about 6 to 7 years (the 6-year molar); the second molar erupts at about age 12 (the 12-year molar); the third molar ("wisdom tooth") may erupt from 17 years onward, or not at all. The 32 permanent teeth are arranged in quadrants of 8 each: 2 incisors, 1 canine, 2 premolars, and 3 molars. The permanent molars have no deciduous predecessors. The Universal System for permanent (adult) dentition includes numbers 1-32 for the usual number of teeth. This numbering system is similar to that for primary dentition and proceeds from the patient's right upper third molar (number 1) to the left upper third molar (number 16). The lower jaw numbering proceeds from left to right (numbers 17 to 32). If looking in the open mouth, this numbering system begins with the most posterior upper (maxillary) tooth on the right and proceeds in a clockwise direction around the mouth from 1-32.
The teeth are arranged, or "aligned," in two arches, or arcades, one in each jaw. The term occlusion is used for any functional relation established when the upper and lower teeth come into contact with each other. Abnormal occlusion is termed malocclusion, the prevention and correction of which is orthodontics.
Berkovitz, B. K. B., Holland, G. R., and Moxham, B. J., A Colour Atlas and Textbook of Oral Anatomy, Wolfe, London, 1978. Nice illustrations of gross anatomy, histology, and embryology.
Scott, J. H., and Symons, N. B. B., Introduction to Dental Anatomy, 8th ed., Churchill Livingstone, Edinburgh, 1977. A readable text on teeth, including an account of the development and growth of the face, jaws, and teeth.
Wheeler, R. C., An Atlas of Tooth Form 4th ed., W. B. Saunders Company Philadelphia, 1969.
Wheeler, R. C., Dental Anatomy, Physiology and Occlusion, 5th ed., W. B. Saunders Company, 1974. These two books are valuable for dental students.
51-1 Where does the parotid duct open?
51-2 What is the opening between the oral cavity and the oropharynx termed?
51-3 Which nerve supplies the muscles of the palate?
51-4 What is the anatomical significance of the sulcus terminalis on the back of the tongue?
51-5 Where are the vallate papillae?
51-6 Where are the valleculae?
51-7 Why is the attachment of the tongue to the mandible important clinically?
51-8 Into which chief lymphatic nodes does the tongue drain?
51-9 What is the difference between the anatomical crown and the clinical crown of a tooth?
51-10 What is the clinical importance of the relationship between the upper molar roots and the floor of the maxillary sinus?
51-11 Why are some teeth called successional and others accessional?
51-12 When do milk teeth appear?
51-13 Which are the first permanent teeth to erupt?
51-14 How are teeth numbered?
51-15 What is occlusion?
Figure 51-1 Views of the open mouth with the tongue protruded (A) and with the tip of the tongue raised (B). (From photographs by Bassett.)
Figure 51-2 A, Dorsum of the tongue, showing the sensory innervation on one side. The numbers refer to cranial nerves. B and C, Diagrams showing the parts of the tongue.
Figure 51-3 Extrinsic muscles of the tongue, right lateral aspect. Most of the right half of the mandible and of the mylohyoid muscle has been removed.
Figure 51-4 Lymphatic drainage of the tongue. A, Right lateral aspect. Note the submandibular and sublingual salivary glands. Each cross-hatched circle represents a group of nodes. JD, jugulodigastric nodes; JOH, jugulo-omohyoid nodes. B, Schematic coronal section. (A is based on Rouviere, B on Jamieson and Dobson.)
Figure 51-5 A, Longitudinal section of an incisor. B, Cross-section of the crown of an incisor, showing enamel, dentin, and pulp. C, Side view of an incisor, showing the area of epithelial attachment and the line of the cemento-enamel junction. D, Longitudinal section of a molar, showing the bifurcation of the pulp cavity.
Figure 51-6 Dental terminology. Upper permanent teeth viewed from below.
Figure 51-7 Right lateral aspect of the maxilla and mandible of a 5-year-old child, showing the position of the deciduous and permanent teeth.
Figure 51-8 Vestibular surfaces of the right deciduous teeth. Abbreviations for cusps and roots: B, buccal; D, distal; L, lingual; M, mesial. (After Wheeler.)
Figure 51-9 Vestibular surfaces of the right permanent teeth. Abbreviations for cusps and roots: B, buccal; D, distal; L, lingual; M, mesial. (After Wheeler.)
Figure 51-10 A, Dental and periodontal tissues from the right side of the mandible of an adolescent. B, Twenty intra-oral films of the permanent teeth. The teeth are being viewed as they would appear from within the oral cavity. (From McCall, J.O., and Wald, S.S., Clinical Dental Roentgenology, 4th ed., W. B. Saunders Company, Philadelphia, 1957, courtesy of the authors.)