The experimental production of odontogenic keratocysts

Longstanding dental pathology in Neandertals from El Sidrón (Asturias, Spain) with a probable familial basis

Two Neandertal specimens from El Sidrón, northern Spain, show evidence of retained left mandibular deciduous canines. These individuals share the same mitochondrial (mtDNA) haplotype, indicating they are maternally related and suggesting a potential heritable basis for these dental anomalies. Radiographs and medical CT scans provide evidence of further, more extensive dental pathology in one of these specimens. An anomalous deciduous canine crown morphology that developed before birth subsequently suffered a fracture of the crown exposing the pulp sometime after eruption into functional occlusion. This led to death of the tooth, periapical granuloma formation and arrested deciduous canine root growth at an estimated age of 2.5 years. At some point the underlying permanent canine tooth became horizontally displaced and came to lie low in the trabecular bone of the mandibular corpus. A dentigerous cyst then developed around the crown. Anterior growth displacement of the mandible continued around the stationary permanent canine, leaving it posteriorly positioned in the mandibular corpus by the end of the growth period beneath the third permanent molar roots, which, in turn, suggests a largely horizontal growth vector. Subsequent longstanding repeated infections of the expanding cyst cavity are evidenced by bouts of bone deposition and resorption of the boundary walls of the cyst cavity. This resulted in the establishment of two permanent bony drainage sinuses, one through the buccal plate of the alveolar bone anteriorly, immediately beneath the infected deciduous canine root, and the other through the buccal plate anterior to the mesial root of the first permanent molar. It is probable that this complicated temporal sequence of dental pathologies had an initial heritable trigger that progressed in an unusually complex way in one of these individuals. During life, this individual may have been largely unaware of this ongoing pathology.

Experimental odontogenic cysts induced by in vitro 4-nitroquinoline 1-oxide (4NQO) treatment of F344 rat incisor tooth germs

This study was designed to establish an experimental animal model for elucidating the early stages of odontogenic cysts and tumors. It involves the in vitro treatment of tooth germs with 4-nitroquinoline 1-oxide (4NQO) at the early bell stage and their subsequent transplantation into the kidney subcapsular space. While all tooth germ transplants of the control group not exposed to the carcinogen showed continued tooth development with no pathological lesions, 21 of 23 4NQO-treated tooth germs developed into similar appearing keratinized cysts with or without associated tooth structures. The remaining two transplants failed to develop cysts and formed only a tooth. The present experimental procedure was effective in inducing keratinized cystic lesions that exhibit some similarities to human odontogenic keratocysts or primordial cysts.

The role of endotoxin and cytokines in the pathogenesis of odontogenic cysts

Odontogenic cysts arise from tooth-forming epithelial residues. The stimulus for the formation of radicular cysts is thought to be endotoxin released from the infected necrotic tooth pulp. However, in keratocysts and follicular cysts, such a stimulus is not present. In order to investigate what drives the cyst epithelium to proliferate, explant media and fluids from 16 radicular cysts, eight keratocysts and seven follicular cysts and explant media from four specimens of non-inflamed gingival tissue were examined for the presence of endotoxin and cytokines. Cyst fluids were also cultured for 72 h in anaerobic and aerobic conditions to detect micro-organisms. Endotoxin from three different bacteria, cytokines [interleukin-(IL) 1 alpha, IL-1 beta and IL-6] as well as prostaglandin E2 (PGE2) were tested in an epithelial cell-proliferation assay. As the cyst epithelium is supported by a connective tissue capsule, the effect of fibroblast culture media on epithelial cell proliferation was also investigated. The results showed significantly higher concentrations of endotoxin in radicular cyst fluid than in the keratocyst or the follicular cyst. None of the cyst fluids contained micro-organisms. Immunoassays demonstrated the presence of IL-1 alpha and -6 in all fluids and explants tested; IL-1 beta was only found in the inflammatory radicular cysts. However, reverse transcriptase-polymerase chain reaction showed that mRNAs for IL-1 alpha, -1 beta and -6 were present in all cyst types. Proliferation studies indicated that endotoxin and the cytokines had a mitogenic effect on epithelia at low concentrations; PGE2 had very little effect at low concentrations, and had an inhibitory effect at high concentrations. Cyst fibroblast culture media had a mitogenic effect on the epithelia that was enhanced by the presence of endotoxin.

Odontogenic cyst induction by periapical infection in rats

The purpose of this study was to test the hypothesis that odontogenic cysts can be induced by periapical infection. Pulp extirpation and reaming beyond the root apices were performed in 53 lower first molars in 27 Sprague-Dawley rats. The cavities were left open to allow continuous contamination by oral bacteria. Animals were killed at 6 and more than 8 months after operation. Odontogenic cysts were found in association with 8/53 teeth in 6 animals. Histologically, cysts were observed around the lower incisors below the first molars. The cyst wall consisted of fibrous connective tissue with inflammation and was lined with keratinized squamous epithelium. The cyst cavity contained a mass of keratin and necrotic debris. These results support the hypothesis that inflammatory stimulation from the apices can cause cystic changes in the enamel epithelium of underlying teeth.

Experimental extra-follicular histogenesis of follicular cysts

An animal model has been developed in which implantation cysts have been produced very close to developing teeth within the jaws of Vervet monkeys. Various deciduous teeth were extracted from both the maxilla and the mandible of 6 young Vervet monkeys. After 4 weeks, full thickness mucoperiosteal flaps were raised in these areas, up to 6 recipient sites were prepared in each monkey by drilling holes in the alveolar bone and small pieces of autogenous palatal mucosa were placed in these graft recipient sites. One monkey was killed after 5, 8, 22 and 25 weeks respectively and 2 after 52 weeks. Of the 33 implants placed, cyst formation occurred from 11 (33%). The distribution of the cysts was irregular in that 4 cysts were produced in each of 2 animals while no cysts were found in another 2 animals. The cysts produced were filled with keratin and lined partly by a thick keratinising epithelium and partly by a thin non-keratinising epithelium only a few cell layers thick. In one of the animals killed after 52 weeks, the follicle of an erupting premolar tooth had collided with one of the cysts resulting in the cyst lining becoming incorporated into the follicle, partly replacing the follicular reduced enamel epithelium and forming now an integral part of the follicle. This observation supports the hypothesis that the follicular odontogenic keratocyst has an extra-follicular origin arising after the eruption of a tooth into a pre-existing cyst cavity.

Human odontogenic keratocyst transplants in nude mice

Specimens from human odontogenic keratocysts were subcutaneously transplanted to nude mice. The transplants were harvested after 14-66 d with a rate of successful recovery of 87%. The histologic epithelial features in the original odontogenic keratocyst and their transplants were essentially similar. This included a well-defined basal cell layer composed of columnar and cuboidal cells, the number of cell layers and the keratinization pattern. Epithelial outgrowths from the transplants were found in 19 of 26 cases. The outgrowths over murine connective tissue in the majority of cases were keratinized, but the phenotypic expression differed with respect to the shape of basal cells and number of cell layers.

Experimental dentigerous cysts and enamel hypoplasia: their possible significance in explaining the pathogenesis of human dentigerous cysts

Cysts lined by epithelium were often found in association with tooth-germ isografts in hamster cheek pouch. They developed from odontogenic epithelium and were in close relation to the crowns of involved teeth. Cysts associated with tooth-germ isografts from 5-day-old animals (17 out of 36) commenced their formation shortly after transplantation as a result of enamel organ degeneration. Teeth associated with these cysts often showed enamel hypoplasia. Accordingly, 86 teeth involved in human dentigerous cysts were examined and 43 were found to possess areas of enamel hypoplasia on their occlusal surfaces or incisal edges. It is suggested that the pathological process initiating cystic degeneration in the enamel organ was also accompanied by degeneration of ameloblasts. When tooth germs from 2-day-old hamsters were transplanted, cystic spaces developed only after completion of enamel formation, 6 weeks following transplantation (in six out of 11 transplants), as a result of separation between the cells of the reduced enamel epithelium. Enamel hypoplasia was not a conspicuous feature. These experimental and clinical observations suggest that there may be at least two types of dentigerous cyst, perhaps with different causes, arising at different stages of tooth development.

An autoradiographic study of experimental odontogenic cyst formation in the mouse

Proliferative populations of cells within the epithelial lining of developing experimental odontogenic cysts were identified by labeling with 3H-thymidine. Mouse molar teeth extracted from 10-day-old mice were transplanted subcutaneously and host animals were injected with 3H-thymidine 1 h prior to sacrifice. The cysts which developed around the crown of the transplanted teeth were prepared for autoradiographical examination. Labeling indices were high initially but decreased rapidly as the cysts enlarged. The pattern of labeling, however, bore no resemblance to the labeling of the reduced enamel epithelium from which the cysts developed. It was concluded that labeling activity reflects only the state of development and activity of the cyst and not the origin of the cyst.

A histological study of odontogenic cysts formed following mouse molar tooth transplantation

The enamel organs of subcutaneously transplanted mouse molar teeth undergo cyst formation and present a model for the study of the pathogenesis of development odontogenic cysts. Maxillary molars extracted from 10-day-old C57B1 mice were grafted subcutaneously into adult mice of the same strain. The grafts were recovered between 2 and 50 days after operation and routinely prepared for histological examination. After initial degeneration, the enamel organ took the form of a squamous epithelium in which after 5 to 6 days squamous hyperplasia took place. Cystic degeneration within the epithelium produced cavities lined with a thick parakeratotic stratified squamous epithelium which resembled the lining of an epidermoid implantation cyst. As the cysts enlarged the lining changed in appearance to a thin squamous non-keratinized epithelium. Similar features have been described in other experimentally produced cysts and in some odontogenic cysts in humans. Their different morphology may arise frominteraction betwen the surrounding connective tissue with epithelium at different stages of development.

Production of keratinizing cysts within mandibles of rats with autogenous gingival epithelial grafts. A histologic study

A method for the consistent production of epithelial-lined cysts in the mandibles of rats is described. Attached gingiva from the interdental papilla was excised and implanted into prepared cavities in the mandible. The animals were examined at time periods varying from 0 to 45 days later. Twenty-seven of the 28 animals examined after 7 days or longer had developed cysts. An interpretation of the pathogenesis of these cysts was made based on histologic observations and measurements of the cysts at the various time intervals.