The oral cavity consists of soft and hard tissues. The lips, cheeks, tongue, gingivae, palate, and tonsils are the former, while the teeth are the latter. The oral cavity is bounded by the lips anteriorly, the nasopharynx posteriorly, the cheeks laterally, the tongue and sublingual tissues inferiorly, and the soft and hard palate superiorly. Various muscles, nerves, and vascular systems contribute to these surrounding structures. The muscles of the oral cavity include mylohyoid, geniohyoid, stylohyoid, hyoglossus, glossopharyngeal, thyroglossus, buccinator, masseter, medial and lateral pterygoid, orbicularis oris, and temporalis. These muscles, together with their tendons, nerves, and blood vessels, keep the oral cavity functional.
1.1 The Lips: Macro Anatomy
The lips are composed of the muscular layer of orbicularis oris, connective tissue, dermis, and mucosa (Figure 1.1). The red vermilion border and its junction with the skin and mucosa at its outer and inner borders may vary in width between races and genders. Lips may have a different posture at rest, including: (i) sealed or competent, and (ii) not sealed or incompetent. Lip position may affect the alignment and profile view of teeth and occlusion (Figures 1.2–1.4). In certain circumstances, the lips appear shorter than normal, or the jaws are not in normal skeletal relationship, with a large part of the maxillary labial gingiva being visible during speech and smile. This condition is often referred to as “gummy” smile (Figure 1.5). Alternatively, there are cases where a longer‐than‐normal lip length or lost vertical height is noted due to lost or missing teeth – for example, ectodermal dysplasia. This in turn could cause the lips to overlap heavily, producing the appearance of an edentulous individual (Figure 1.4).
1.2 The Palate
The palate is divided into two major parts – soft and hard palate, with each of them having specific characteristics related directly to the role they play in different oral functions. The hard palate is supported by a hard, bony structure in the roof of the mouth, while the soft palate is mainly supported by fibrous tissue. The hard palate is covered with keratinized membrane, with a prominent eminence at the anterior mid‐line located on top of the incisive foramen of maxillary bone, called the “incisive papilla.” The nasopalatine nerve and blood supply pass through this foramen. “Rugae” are the anterior rough mucosal folds of the palate located on either side of the incisive papilla and midline raphe (Figures 1.6 and 1.7).
The soft palate, in contrast, consists of muscles, salivary glands, and neurovascular components. The uvula is a soft, small, double‐sided eminence of soft tissue located at the postero‐inferior aspect of the soft palate. During swallowing, the soft palate and the uvula move together to close off the nasopharynx, preventing food from entering the nasal cavity.
1.3 The Tongue
The tongue is a muscular structure attached to the floor of the mouth at it’s posterior. The ventral part of the tongue is covered with a thinly keratinized mucosal membrane firmly attached to the underlying muscles. The lingual frenulum is a thin layer of membranous tissue that attaches the anterior half of the tongue at its midline to the muscular structures in the floor of the mouth. The dorsal surface of the tongue is divided into two parts; the anterior two‐third, and the posterior one‐third (also known as the “pharyngeal” part). The border between these two segments is a shallow “V”‐shaped groove, with the apex of the “V” lying posteriorly. Occasionally, there is a pit located at this apex, known as the “foramen caecum.” The dorsal part of the tongue contains several types of papillae that function as taste organs: filiform; fungiform; foliate (Figures 1.8–1.10); and circumvallate forms.