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 together, 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.