Dentition and Supporting Structures

Typically, there are 32 teeth present in the oral cavity of an adult, with the first permanent tooth generally appearing by age 6 years. There are 20 primary teeth in childhood. Teeth are classified as central and lateral incisors, canines, premolars, and molars. There are no premolars or third molars in the primary dentition. Third molars appear in the mid to late teenage years, but many times do not have adequate space to erupt, often resulting in impaction, and may cause pain and/or infection. Permanent teeth may be classified according to different systems, but the most common method used in the United States is the Universal numbering system.3,4 In this system, teeth are counted starting from the right maxilla (#1 for the right maxillary third molar) to the left maxilla (#16 for the left maxillary third molar), continuing to the left mandible (#17 for the left mandibular third molar) and ending in the right mandible (#32 for the right mandibular third molar) (Fig. 1). The primary teeth are labeled using the alphabet, starting with the letter A for the second primary molar in the right maxilla and ending with the letter T for the second primary molar in the right mandible.4

Each tooth is divided into 2 parts, the crown and the root(s). The outer portion of the crown is covered by enamel, the hardest substance in the body. Dentin, which is immediately below the enamel layer, forms the bulk of the tooth and can be sensitive if the protective enamel is lost. The soft tissue containing the blood and nerve supply to the tooth (pulp) is housed within the dentin, extending from the tip of the root to the crown. A layer of cementum covers the root, which aids in attaching the tooth to the bony socket (Fig. 2).

Supporting structures of the teeth (periodontium) include the periodontal ligament, gingival tissue, bone, blood, and nerves. The periodontal ligament is made up of thousands of fibers, which fasten the cementum to the bony socket and alveolar bone, and act as shock absorbers for the teeth, which are subjected to heavy forces during function. These ligaments also function as sensory, nutritive, and remodeling structures surrounding the roots. Gingival tissue covers teeth and bone to protect them and provides an easily lubricated surface. The alveolar portions of the maxillary and mandibular bones contain sockets to support the roots of the teeth. Each tooth and periodontal ligament has a nerve supply, and the teeth are sensitive to a wide variety of stimuli. The blood supply is necessary to maintain the vitality of the tooth. The maxillary and mandibular divisions of the trigeminal nerve innervate the teeth and the periodontium.

Lips and Oral Mucosa

The lips are musculofibrous structures that are critical to eating, swallowing, speaking, whistling, singing, expectoration, and common human behavioral communications, such as kissing, smiling, and pouting. The lips are composed of 4 tissue layers: cutaneous, muscular, glandular, and mucosa. The juncture where the lips meet the surrounding skin of the mouth is the vermillion border. The areas of the upper and lower lip meet at the corner of the mouth and are called labial commissures. The commissure is important in facial appearance, particularly during functions such as smiling. The maxillary and mandibular branches of the trigeminal nerve (V2 and V3, respectively) innervate the upper and lower lips. The infraorbital branches of V2 innervate the upper lip and the surrounding skin of the face between the upper lip and the lower eyelid, except for the bridge of the nose. The mental nerve branch of V3 innervates the lower lip, mucosa, and the labial gingival tissues anteriorly. The facial artery supplies the blood to the lips.5–8

Tongue and Floor of the Mouth

The tongue occupies the major part of the oral cavity and oropharynx. The tongue has several important functions, including swallowing, mastication, speech, and taste. Tongue movements also help clear food debris from the oral cavity. The major salivary glands, parotid, submandibular (or submaxillary), and sublingual glands, produce saliva to assist with swallowing. Five cranial nerves contribute to the complex innervation of this multifunctional organ. Motor innervation for all of the muscles of the tongue comes from the hypoglossal nerve (cranial nerve [CN] XII), with the exception of the palatoglossus, which is supplied by the pharyngeal plexus (fibers from the cranial root of the spinal accessory nerve carried by the vagus nerve [CN X]).

General sensation of the anterior two-thirds of the tongue is supplied by the lingual nerve, a terminal branch of V3. Taste sensation for this portion of the tongue is carried by the chorda tympani branch of the facial nerve (CN VII). The posterior one-third of the tongue relays general sensation via the lingual-tonsillar branch of the glossopharyngeal nerve (CN IX). Some general and taste sensation from the base of tongue anterior to the epiglottis is carried by the internal laryngeal branch of the superior laryngeal nerve (CN X).

The surface of the tongue is covered by various projections of lamina propria covered with epithelium known as lingual papillae. There are 4 types of papillae: circumvallate (vallate), foliate, filiform, and...