Reduced enamel epithelium forms from the internal and external enamel epithelium and embraces the fully formed crown of an unerupted tooth. This gives rise to the dentigerous (and eruption) cyst (Chapters 5 and 6, Box 5.3, Figures 5.18 and 5.19). The reduced enamel epithelium also forms the junctional or sulcular epithelium during tooth eruption and this gives rise to inflammatory collateral cysts (Chapter 4)
Cell rests of the dental lamina (‘glands of Serres’)
After tooth formation is complete the dental lamina disintegrates, but residual islands are retained in the gingival mucosa and alveolar bone. Cell rests are particularly common in the posterior mandible, where they may also be found in the gubernacular cord or canal (discussed in detail in Chapters 7, 8, 9, and 12; see Figures 7.12, 8.3, 9.7, and 9.9)
Non‐odontogenic cysts
Nasopalatine duct cyst
Remnants of the nasopalatine duct
The nasopalatine duct is a fetal structure and involutes at about 10 weeks of intrauterine life. Residual epithelial remnants, however, may remain in the incisive canal after birth and in adults (Chapter 13, Figure 13.1, Box 13.1)
Nasolabial cyst
Nasolacrimal duct
The nasolacrimal duct forms after 6 weeks of intrauterine life and drains tears from the lacrimal sac to the lower aspect of the lateral nasal wall. Residual epithelial remnants may persist at the inferior portion of the duct (Chapter 14)
Mid‐palatal raphe cyst (Epstein pearls)
Epithelial inclusions
The palatal shelves fuse at about 7–8 weeks of intrauterine life. The epithelial coverings fuse and then break down into many small islands, many of which form small ‘microcysts’ (Figure 9.7). Most involute before birth, but up to 80% of newborns may have cysts up to 3 months of age (Chapter 9). There is some evidence that inclusions may arise in the bone and give rise to an intraosseous ‘median palatal cyst’ (discussed in Chapter 13)
Surgical ciliated cyst
Remnants of respiratory epithelium
Fragments of sinus epithelium become implanted into a wound following surgery involving the maxillary sinus (Chapter 16)
Cysts of the salivary and minor mucous glands
Mucous retention cysts
Ducts of minor mucous glands
The ducts of minor mucous glands become blocked and dilated, most often as a result of trauma (Figures 15.5, 15.6, and 15.10)
Salivary duct cyst Lymphoepithelial cysts
Intraparotid ducts
The pathogenesis is uncertain, but blockage of ducts associated with sialadenitis may cause cystic dilatation (Figure 15.12)
Intraoral lymphoepithelial cysts
Tonsillar crypt epithelium
The opening of intraoral tonsils may become blocked, causing cystic dilatation of the crypt. Some intraoral lymphoepithelial cysts may be retention cysts arising from a superficial duct of minor salivary glands
Developmental cysts of the head and neck
Intraoral dermoid and epidermoid cysts
Epithelial inclusions
Epithelial remnants are sequestered into the tissues during fusion of facial processes. Oral dermoid and epidermoid cysts are found in the anterior oral cavity at sites of fusion of the mandibular processes (Box 18.1)
Intraoral cysts of foregut origin
Epithelial inclusions
Oral foregut cysts arise from epithelial remnants following fusion of the tuberculum impar (first branchial arch) and the posterior one‐third of the tongue (second to fourth arches) (Box 18.2)
Branchial cleft cysts
Epithelial inclusions
Branchial cleft cysts arise from epithelial remnants that become entrapped or persist due to incomplete obliteration of the branchial clefts or pharyngeal pouches (Box 18.3)
Thyroglossal duct cyst
Remnants of the thyroglossal duct
The thyroid gland develops at about 4 weeks of intrauterine life in the dorsum of the tongue. The developing gland descends downwards into the upper neck forming the thyroglossal duct, which then disintegrates. However, residual epithelial remnants are found in the midline of the upper neck and tongue in about 40% of people (Box 18.4)
In the majority of odontogenic cysts, the epithelial lining is derived from epithelial remnants of the dental lamina (Table 2.1). Early in the development of the jaws, the surface epithelium thickens and grows downwards into the mesenchyme of the future dental arches to form the dental lamina. This extends around the arch as a band that maps the future sites of tooth bud formation for both primary and secondary dentitions. The teeth develop as a result of complex epithelial–mesenchymal interactions that result in epithelial thickenings or placodes, which then form the enamel organs that pass through the well‐described bud, cap, and bell stages during formation of the fully developed tooth (Nanci 2017 ). The dental lamina remains as a thin band that joins the surface oral epithelium to the enamel organ and
