<unk> s develop due to an inflammatory stimulus in 3 stages: # Initial stage: Epithelial cells from the rests of Malassez at the apex of the roots of a non-vital tooth (one where the nerve and blood supply in the tooth have degenerated and no longer exist) become stimulated due to the body's inflammatory response to bacterial endotoxins infecting the pulp or as a direct response to necrotic pulp tissue, therefore re-entering the growth phase. Bacterial byproducts then are able to seep into the<unk>  region through the infected pulp. # Cyst development stage: Epithelial cells form strands and are attracted to the area which contains exposed connective tissue and foreign substances. Several strands from each rest converge and surround the abscess or foreign body. # Cyst growth stage: Fluid flows into the cavity where the forming cyst is growing due to the increased osmolality of the cavity in relation to surrounding serum in capillaries. Pressure and size increase. The definitive mechanism by which cysts grow is under debate; several theories exist. Biomechanical theory Pressure and concentration differences between the cystic cavity and the growth surroundings influence fluid movement into the cyst, causing size increase. Biochemical theories a. Collagenase (breakdown of collagen) in the jaw bone leads to bone degeneration, providing room for cysts to develop. Substances released by the body's immune system as a result of the connective tissue breakdown, such as cytokines and growth factors, contribute to the mobilization and proliferation of epithelial cells in the area. b. Bone resorption caused by metabolism of acidic substances produced by cysts contributes to cyst growth. Such substances include Prostaglandin-2 and Interleukin-1 which are both produced by the cyst itself. Nutritional deficiency theory Epithelial cells will form a mass inside the cavity and the innermost cells become deprived of nutrients because they are far from the source of nutrients (the blood vessels). The innermost cells die and form an aggregate of dead tissue. The inner cells undergo ischemic liquefactive necrosis which creates the cavity space surrounded by growing epithelial cells. This theory is unlikely in the absence of malignant transformation of epithelial cells as it does not follow the existing relationship between connective tissue and epithelium. Abscess theory Epithelial cells have an inherent quality to reproduce and cover any connective tissue that is not already lined with epithelia. Formation of an abscess must precede the epithelial proliferation in order for the cells to carry out this tendency. This theory explains why cysts are lined in epithelia but not why the initial cysts itself forms.
Periapical cyst
Subareolar abscess
Nabothian cyst
Proliferating trichilemmal cyst
Keratin implantation cyst
Trichilemmal cyst
Limbal nodule
Genu recurvatum