Odontogenic cysts and tumours arise from inclusion of tooth-forming epithelium and mesenchyme in the jaw bones during development. Cysts also arise from non-odontogenic epithelium trapped during fusions or from vestigial structures. In addition, bone cysts that can arise at other skeletal sites may also occur in the jaws. Odontogenic cysts and tumours may be classified according to their putative developmental origins and biology. The classification of jaw cysts is shown in Fig. 6.1. Odontomes are hamartomatous developmental lesions of the tooth-forming tissues. Odontogenic tumours are uncommon and are usually benign. Ameloblastoma is the most common odontogenic tumour and is described in detail. The other odontogenic tumours are rare and only the principal features are presented. Very rare congenital lesions of possible odontogenic origin are mentioned in the final section. A cyst may be defined as pathological cavity lined by epithelium with fluid or semi-fluid contents. However, clinically, the term encompasses a broader range of benign fluid-filled lesions, some of which do not possess an epithelial lining. The preferred definition is, therefore, ‘a pathological cavity having fluid or semi-fluid contents that has not been created by the accumulation of pus’. Cysts are commonly encountered in clinical dentistry and are generally detected on radiographs or as expansions of the jaws. Most cysts have a radiolucent appearance and are well circumscribed, often with a corticated outline. At least 90% of jaw cysts are of odontogenic origin. The clinico-pathological features of jaw cysts are summarized in Table 6.1. The incidence of the four most common jaw cysts are provided in Table 6.2. The epithelial lining of odontogenic cysts originates from residues of the tooth-forming organ. • Epithelial rests of Serres are remnants of the dental lamina and are thought to give rise to the odontogenic keratocyst, lateral periodontal, and gingival cysts. • Reduced enamel epithelium is derived from the enamel organ and covers the fully formed crown of the unerupted tooth. The dentigerous (follicular) and eruption cysts originate from this tissue, as do the mandibular buccal and paradental cysts. • Epithelial rests of Malassez form by fragmentation of Hertwig’s epithelial root sheath that maps out the developing tooth root. Radicular cysts originate from these residues.
A Clinicopathological Report of Four Cases of Squamous Odontogenic Tumor-Like Proliferations in Odontogenic Cysts: Suggested Opinions regarding This Unusual Nature
