A dentigerous cyst is an epithelial-lined cyst which involves the crown of an unerupted tooth in its cavity.

Source :Origin and growth of cysts of the jaws. Ann R Coll Surg Engl. 1967 May; 40(5): 306–336.

The cysts are the second most prevalent type of odontogenic cysts after radicular cysts. They are usually painless, and many patients (and their dentists) are unaware of them until a routine x-ray is performed.

The reasons for their development are currently unexplained.

It has been suggested (Thoma, 1960) that dentigerous cysts originated by a degeneration of the stellate reticulum of the enamel organ, the central type originating over the axis of the crown, the lateral type presumably starting a little later in the crown development. However, it has long been observed that teeth contained within a dentigerous cyst generally do not suffer from abnormalities of enamel.

[Source as above]