There were three possible mechanisms exist. Firstly, surrounding the crowns of affected teeth, the intrafollicular developmental dentigerous cysts may be formed. These cysts may be secondarily inflamed and infected as a result of periapical inflammation spreading from non vital deciduous predecessors. Benn and Altini (1996) claimed that this possibility was unlikely as all the cases reported were not associated with tooth impaction. Secondly, radicular cysts developed at the apices of non vital primary teeth. These radicular cysts may fuse with the follicles of the unerupted successors, causing the eruption of the successors into the cyst cavity. This may result in the formation of extrafollicular dentigerous cyst. Shear regarded this to be exceptionally rare because radicular cyst is uncommon in the primary dentition. The third possibility is that periapical inflammation could be of any source but usually from a non vital deciduous tooth spreading to involve the follicles of unerupted permanent successors. The inflammatory exudate causes separation of reduced enamel epithelium from the enamel with resultant cyst formation. Clinical Features
The dentigerous cyst commonly involves a single tooth and rarely affects multiple teeth. The most frequently involved tooth is the mandibular third molar followed by the maxillary canine, but they may be associated with supernumerary or ectopic tooth. Any permanent tooth can be involved. Regezi and Sciubba stated that the impacted teeth were most commonly seen in the third molar and maxillary canine teeth, and hence dentigerous cysts occur most frequently in these teeth. The involved teeth may be displaced into ectopic positions.
A hemizygous deletion or mutation of the STS gene in a male results in complete absence of enzyme activity, while a female carrier of a mutation or deletion is heterozygous and still has a normal copy of the STS gene. Female carriers of an STS deletion or mutation still express the STS enzyme, although with decreased enzyme activity.For this reason, XLI most commonly affects males, although individuals with numeric abnormalities of the sex chromosomes (45,X and 47,XXY) who also carry STS deletions or mutations would be exceptions to this rule.In addition, a female could be affected if she were the offspring of an affected male and a carrier female and inherited a deletion or mutation of the STS gene on both X chromosomes. Genetic counseling issues
Since the majority of cases appear to occur through transmission of an STS deletion from a carrier mother, enzyme testing or DNA testing should be performed in the mother of any newly diagnosed simplex case (i.e. the first case in a family). In the case of an extended family with many affected individuals, carrier status can often be assigned based on pedigree analysis. Males with XLI will transmit the X chromosome harboring the STS deletion or mutation to each of his female offspring, who will therefore be an obligate carrier. However, all male offspring will be unaffected, since they receive their fathers Y chromosome. Female carriers of an STS deletion or mutation have a 50% chance with each pregnancy of transmitting it to an offspring.