Oral Cavity

The oral cavity extends from the lips to the palatoglossal folds. The outer vestibule is enclosed by the cheeks and lips and forms a slit-like space separating it from the gingivae and teeth. It is limited above and below by mucosal reflections from the lips and cheeks.

The space bordered by the teeth and gin-givae is the oral cavity proper. It is bounded inferiorly by the floor of the mouth and tongue and superiorly by the hard palate. The buccal mucosa extends from the commissure of the lips anteriorly to the palatoglossal fold posteriorly. It is lined by thick, non-keratinized stratified squamous epithelium and contains variable numbers of sebaceous glands (Fordyce spots or granules) and minor salivary glands. The duct of the parotid gland (Stensen's duct) opens on a papilla or fold opposite the upper second permanent molar tooth. The mucous membrane related to the teeth is the gingiva. The gingival mucosa surrounds the necks of the teeth and the alveolar mucosa overlies the alveolar bone and extends to the vestibular reflections. The junction between these two parts is marked by a faint scalloped line called the mucogingival junction. The gingival mucosa is pink and firmly attached to the underlying bone and necks of the teeth (attached gingiva) except for a free marginal area. It is usually non-keratinized or parakeratinized. The alveolar mucosa is reddish and covered by thin, non-kera-

tinized stratified squamous epithelium. Minor salivary glands may be seen in the alveolar mucosa and occasionally the attached gingiva.

The hard palate is continuous anteriorly with the maxillary alveolar arches and posteriorly with the soft palate. A median raphe extends anteriorly from this junction to the incisive fossa into which the nasopalatine foramen opens. Most of the palatal mucosa is firmly bound to the underlying bone forming a mucoperios-teum. It is covered by orthokeratinized stratified squamous epithelium and posteriorly contains many minor mucous salivary glands.

The oral part of the tongue (anterior two thirds) lies in front of the V-shaped sulcus terminalis. It is mobile and attached to the floor of the mouth anteriorly by a median lingual fraenum. The dorsal part is covered by stratified squamous epithelium and contains several types of papillae. The most numerous are the hair-like filiform papillae which are heavily keratinized. There are less numerous and evenly scattered fungiform papillae which form pink nodules and contain taste buds. Taste buds here and in other oral sites are occasionally mistaken for junctional melanocytic proliferation or Pagetoid infiltration. In front of the sulcus terminalis there are 10-12 circumvallate papillae. These contain many taste buds on the surface and in a deep groove that surrounds each papilla. In addition, the ducts of minor serous salivary glands

Fig. 4.1 Taste buds. Normal intraepithelial taste buds are sometimes confused with melanocytic lesions and pagetoid infiltration..

(von Ebner's glands) open Into the base of the groove. At the postero-lateral aspect of the tongue where it meets the palatoglossal fold there are the leaf shaped foliate papillae. These also may contain taste buds on the surface and the core of the papillae often contains lym-phoid aggregates similar to those in the rest of the Waldeyer ring. In addition, there are minor salivary glands in the underlying lingual musculature. The ventrum of the tongue is covered by thin, non-keratinized stratified squamous epithelium which is continuous with similar mucosa in the floor of the mouth. Minor salivary glands (glands of Blandin and Nuhn) are present, predominantly towards the midline and deep within the lingual musculature. They can extend to involve the tip of the tongue. The floor of the mouth is a horseshoe-shaped area between the ventrum of the tongue medially and the gingivae of the lower teeth anteriorly and laterally. It extends to the palatoglossal folds distally and is in continuity with the retromolar pad behind the lower third molar tooth. The mucosa covers the major sublingual glands and the submandibular (Wharton's) ducts which open anteriorly onto the submandibular papillae on either side of the median sublingual fraenum. It is important to note that 75% of oral squa-mous cell carcinomas have been reported to arise in an area that comprises the floor of the mouth and adjacent lingual mucosa, sublingual sulcus and retromolar region {1767}. This region forms only about 20% of the total mucosal area. The zone of increased susceptibility has been called the 'drainage area' as it is thought that any carcinogens present in the mouth pool there before being swallowed. It is obvious, therefore, that any precursor lesions in these areas should be regarded as highly suspicious.

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