A cyst is a pathological epithelial lined cavity that fills with fluid or soft material and usually grows from internal pressure generated by fluid being drawn into the cavity from osmosis (hydrostatic pressure). The bones of the jaws, the mandible and maxilla, are the bones with the highest prevalence of cysts in the human body. This is due to the abundant amount of epithelial remnants that can be left in the bones of the jaws. The enamel of teeth is formed from ectoderm (the precursor germ layer to skin and mucosa), and so remnants of epithelium can be left in the bone during odontogenesis (tooth development). The bones of the jaws develop from embryologic processes which fuse, and ectodermal tissue may be trapped along the lines of this fusion. This "resting" epithelium (also termed cell rests) is usually dormant or undergoes atrophy, but, when stimulated, may form a cyst. The reasons why resting epithelium may proliferate and undergo cystic transformation are generally unknown, but inflammation is thought to be a major factor. The high prevalence of tooth impactions and dental infections that occur in the bones of the jaws is also significant to explain why cysts are more common at these sites.
Cysts that arise from tissue(s) that would normally develop into teeth are referred to as odontogenic cysts. Other cysts of the jaws are termed non-odontogenic cysts. Non-odontogenic cysts form from tissues other than those involved in tooth development, and consequently may contain structures such as epithelium from the nose. As the cyst grows from hydraulic pressure it causes the bone around it to resorb, and may cause movement of teeth or other vital structures such as nerves and blood vessels, or resorb the roots of teeth. Most cysts do not cause any symptoms, and are discovered on routine dental radiographs. Some cysts may not require any treatment, but if treatment is required, it usually involves some minor surgery to partially or completely remove the cyst in a one or two-stage procedure.
Classification
Odontogenic cysts
Odontogenic cysts have histologic origins in the cells of the dental structures. Some are inflammatory while others are developmental. Radicular cyst is the most common (up to two thirds of all cysts of the jaws). This inflammatory cyst originated from a reaction to dental pulp necrosis. Dentigerous cyst, the second most prevalent cyst, is associated with the crown of non-erupted tooth. Odontogenic keratocyst This lesion may be associated with the Nevoid basal cell carcinoma syndrome. Buccal bifurcation cyst which appears in the buccal bifurcation region of the mandibular first molars in the second half of the first decade of life. Eruption cyst; a small cyst in the gingiva as a tooth erupts, forming from the degenerating dental follicle Primordial cyst; previous thought to be a unique entity. Most primordial cysts have proven to be Keratocystic odontogenic tumors Orthokeratinized odontogenic cyst; a variant of the Keratocystic odontogenic tumor Gingival cyst of the newborn; an inclusion cyst from remnants of the dental lamina on a newborn gingiva Gingival cyst of the adult; a soft tissue variant of the lateral periodontal cyst Lateral periodontal cyst; a non-inflammatory cyst (vs a radicular cyst) on the side of a tooth derived from remanents of the dental lamina Calcifying odontogenic cyst; a rare lesion with cystic and neoplastic features and significant diversity in presentation, histology and prognosis Glandular odontogenic cyst; cyst with respiratory like epithelial lining and the potential for recurrence with characteristics similar to a central variant of low-grade mucoepidermoid carcinoma
Developmental/ Non-odontogenic cysts
There are several development cysts of the head and neck most of which form in the soft tissues rather than the bone. There are also several cysts, previously thought to arise from epithelial remanents trapped in embryonic lines of fusion, most of which are now believed to be odontogenic in origin or have an unknown cause. Their names are included for the sake of completeness.
Developmental cysts of the jaws
Nasopalatine duct cyst, the most common development jaw cyst, appears only in the mid-line of the maxilla.
Developmental cysts of the soft tissues around the jaws
Palatal cysts of the newborn (Epstein's pearls) Nasolabial cyst (nasoalveolar cyst) Epidermoid cyst of the skin Dermoid cyst Thyroglossal duct cyst Branchial cleft cyst (cervical lymphoepithelial cyst) Oral lymphoepithelial cyst