Review the panoramic radiograph. Considering the impacted mandibular third molars indicated by the arrows, all of the following are recognized potential future complications EXCEPT:

Correct answer: D. Primordial (primary) cyst formation

• A. EXTERNAL ROOT RESORPTION of the second molar occurs where the impacted crown presses directly against its distal root surface — a recognized indication for prophylactic removal.
• B. DISTAL CARIES on the second molar is one of the most common and most damaging consequences of a mesioangular impaction. The contact area is impossible for the patient to clean, and the lesion is frequently deep before it is detected.
• C. RECURRENT PERICORONITIS is the classic complication of a partially erupted third molar, arising from bacterial stagnation beneath the operculum.
• D. CORRECT as the EXCEPTION. A PRIMORDIAL CYST arises from a tooth germ that degenerates BEFORE any calcified tissue forms — meaning it develops INSTEAD OF a tooth, in place of one that never came to exist. Since these third molars are clearly present and fully formed on the radiograph, a primordial cyst in their position is not possible. The cyst these impacted teeth could actually produce is a DENTIGEROUS cyst, arising from the follicle surrounding the crown of an unerupted tooth.

Note: Distinguish the odontogenic cysts: DENTIGEROUS — attached at the CEJ, surrounds the crown of an UNERUPTED tooth (this is the relevant one here). PRIMORDIAL — forms in place of a tooth that never developed. RADICULAR — at the apex of a NON-VITAL tooth. Note that many primordial cysts, on histological review, prove to be odontogenic keratocysts.