Chapter 1 Oral Structures and Tissues Arthur R. Hand1 and Marion E. Frank2 1 Department of Craniofacial Sciences and Cell Biology , School of Dental Medicine, University of Connecticut 2 Department of Oral Health and Diagnostic Sciences , University of Connecticut The oral cavity and its component cells, tissues, and structures the lips and the mucosa lining the inside of the lips, and extends constitute a unique and complex organ system and environment. posteriorly to the palatoglossal folds or arch . Beyond the palato- Of necessity, we study its various parts individually, but the glossal folds are the palatopharyngeal folds and the beginning health and function of the components of the oral cavity depend of the oropharynx , where the digestive and respiratory tracts upon and influence one another. Importantly, the oral cavity come together. The palatine tonsils are located in the tonsillar relies on as well as influences the health and function of the fauces between the palatoglossal and palatopharyngeal folds. entire body. The lymphoid tissue of the palatine tonsils, along with that of the The oral cavity is the gateway to the body, and most of the pharyngeal tonsil ( adenoids ) and the lingual tonsils , guards the substances that enter our bodies do so through the oral cavity. It entrance to the oropharynx. Anteriorly, the respiratory tract is exposed to the physical insults of mastication, hard objects and (nasal cavity) is separated from the oral cavity by the hard palate , various food substances, and extremes of temperature. A variety and posteriorly by the soft palate . The hard palate has an arch-like of chemicals, including those present in foods and drinks and shape that varies in width and height among individuals. It also produced by commensal and pathogenic organisms, affect the plays an important role in manipulation and mastication of food, oral cavity. It functions in alimentation, respiration, innate and and in speech. The soft palate functions to seal the oropharynx immune defense, special and general sensation, speech, and from the nasopharynx during swallowing and speech. However, human interactions. The tissues and structures of the oral cavity during exhalation, receptor cells that detect odors in the olfactory are subject to unique as well as general disease processes. mucosa are activated by oral vapors moving from the posterior Diseases originating in the oral cavity can have systemic effects; oral to posterior nasal cavity through the nasopharynx, effectively likewise, systemic diseases can affect theCOPYRIGHTED oral cavity and the first expanding MATERIAL the mouth. It is this retronasal route that gives food signs and symptoms of many diseases may appear in the mouth. and drink the odors that contribute much to flavor perception. The lips and cheeks are separated from the alveolar processes of the maxilla and mandible that support and hold the teeth by a The oral cavity space called the vestibule . The vestibule is limited posteriorly by The readily visible components of the oral cavity include the lips the ramus of the mandible, and superiorly and inferiorly by the ( labia ), the inside of the cheeks ( bucca ), the teeth and gums mucolabial and mucobuccal folds . The mucosal lining of the ( gingivae ), the hard and soft palates, the floor of the mouth, and vestibule is continuous with the mucosa of the lips and cheeks, the tongue (Fig. 1.1 ). Not visible, but clearly important, are the and with the mucosa covering the alveolar processes (Fig. 1.2 ). muscles, nerves, blood vessels, glands, joints, and especially the Folds ( frena [singular, frenum ]) of the mucosa, located at the bones of the upper ( maxilla ) and lower ( mandible ) jaws that midline and in the canine regions, extend across the vestibule to provide support for and function with the visible components. anchor the lips and cheek to the maxilla and mandible. The The oral cavity begins at the junction of the vermilion border of secretions of the parotid salivary gland enter the vestibule Fundamentals of Oral Histology and Physiology, First Edition. Arthur R. Hand and Marion E. Frank. © 2014 John Wiley & Sons, Inc. Published 2014 by John Wiley & Sons, Inc. Chapter No.: 5 Title Name: Hand 0002192172.indd 0002192172.indd 1 10/18/2014 5:59:21 PM Comp. by: Sivaranjini Date: 18 Oct 2014 Time: 05:59:20 PM Stage: Proof WorkFlow:CSW Page Number: 1 2 Fundamentals of Oral Histology and Physiology Superior lip (pulled upward) Superior labial frenum Gingivae Palatoglossal fold Fauces Hard palate Palatopharyngeal fold Soft palate Uvula Palatine tonsil Cheek Tongue (lifted up) Molars Lingual frenum Premolars Opening of duct of Canine submandibular gland Incisors Gingivae Inferior labial frenum Vestibule Inferior lip (pulled down) Figure 1.1 Diagram illustrating the anatomy and main structures of the oral cavity. (Modified from Tortora , G.J. & Grabowski , S.R. 2000 . Principles of Anatomy and Physiology , 9th edition , Wiley , New York . Reproduced by permission of John Wiley & Sons.) Mandibular incisors 1st Central Lateral Canine premolar Mucogingival junction Labial frenum Attached Alveolar Interdental Free gingiva mucosa papilla gingiva Figure 1.2 Oral mucosa, gingivae and mandibular teeth. Blood vessels visible through the thin non-keratinized epithelium of the alveolar mucosa give it a redder color than the gingivae with their thicker keratinized epithelium. (From http://commons.wikimedia.org/wiki/File:Healthy_ gingiva.jpg ) through its main duct, which opens at the parotid papilla on the The attached gingiva is firmly bound to the bone of the alveolar buccal mucosa opposite the maxillary second molar tooth. process, and through the junctional epithelium is bound to and The mucosa surrounding the necks, or cervical regions of the creates a seal around each tooth. The free gingiva is separated teeth, is called the gingivae. The attached gingiva is clearly demar- from the tooth by the gingival sulcus or crevice , and forms the cated from the alveolar mucosa at the mucogingival junction . interdental papilla between adjacent teeth. 0002192172.indd 2 Chapter No.: 5 Title Name: Hand 0002192172.indd10/18/2014 5:59:28 PM Comp. by: Sivaranjini Date: 18 Oct 2014 Time: 05:59:20 PM Stage: Proof WorkFlow:CSW Page Number: 2 Chapter 1 Oral Structures and Tissues 3 The tongue occupies the space within the maxillary and man- parakeratinized epithelium, and is found on surfaces subjected dibular arches, from the floor of the mouth to the hard and soft to the stresses induced by chewing our food (mastication), the palates. The mucosa of the dorsal surface of the tongue has sev- hard palate and the gingivae. Specialized mucosa is found on eral types of specialized structures called papillae that function the dorsal surface of the tongue. This mucosa is considered spe- in the manipulation of food and in taste. The tongue also is criti- cialized because it forms four different types of papillae , three cal for forming proper speech sounds. The anterior portion of of which have taste buds through which taste sensations are the tongue is anchored to the floor of the mouth by the lingual received. Multiple fungiform papillae dot the dorsal anterior frenum . The ducts of the submandibular and sublingual lingual surface, whereas two series of papillae with associated salivary glands open on either side of the lingual frenum at the trenches or troughs, the medial circumvallate and lateral foliate sublingual caruncle ; smaller ducts of the sublingual gland open papillae, are found far posterior near the base of the tongue along the sublingual fold on each side of the floor of the mouth. (Fig. 1.4 ). The walls of the trenches are lined with specialized mucosa containing taste buds. The ducts of minor salivary glands ( von Ebner’s glands ) open into the trenches, and sub- Oral mucosa stances present in the trenches are flushed out by their secre- Mucosa is a wet, soft tissue membrane that lines an internal tions. Because the mucosa of the tongue has a stratified body space, e.g., the oral cavity, the gastrointestinal, urinary, and squamous keratinized epithelium, and because it plays an reproductive tracts. The oral mucosa consists of three layers: a important role in mastication of food, this mucosa also may be surface epithelium ; a supporting lamina propria consisting of classified as masticatory mucosa. a layer of loose connective tissue (papillary layer ) just below the The oral mucosa has several functions. These include provid- epithelium and a deeper layer of dense irregular connective tis- ing protection from physical and chemical insults through its sue ( reticular layer ); and an underlying submucosa consisting of multilayered and keratinized epithelial surface; serving as a per- dense irregular connective tissue (Fig. 1.3 ). The submucosa fre- meability barrier to prevent passage of microorganisms and quently contains minor salivary glands , and in some locations toxic materials; detecting and responding to pathogenic micro- may contain adipose tissue. In some regions of the oral cavity, organisms and foreign antigens through its immunological com- the submucosa may be absent, and the mucosa is bound to ponents; lubricating and moistening the oral surfaces through either bone or muscle by the lamina propria. secretion of fluid and mucins ; and general and special sensation Three subtypes of mucosa are found in the oral cavity. Lining through free and encapsulated nerve endings and taste buds. or moveable mucosa has a stratified squamous non-keratinized epithelium , and is found on the inside of the lips and cheeks, in the vestibules and the floor of the mouth, and on the alveolar pro- cesses, the ventral surface of the tongue, and the soft palate. Masticatory mucosa has a stratified squamous keratinized or Epithelium Papillary layer Lamina propria Reticular layer Minor salivary Submucosa gland Nerve & vein Bone Figure 1.4 Light micrograph of a section through a foliate papillary trench of the tongue of a hamster. Arrows point to taste buds in the epithelial lining of the trench.