What is the diagnosis for an X-ray with a remaining left second molar, absent third molar?

The presence of a left second molar on X-ray with an absent third molar suggests the possibility of a primordial cyst. Primordial cysts are dental cysts that arise in the place of a tooth that has failed to develop, typically occurring in association with an unerupted tooth or in areas where teeth are missing. In this case, the absence of the third molar may indicate that it did not develop, leading to the formation of a primordial cyst in that area.

This cyst is often noted in young patients and can appear similar radiographically to other cyst types, but its unique association with the absence of a specific tooth helps in identifying it. Understanding this context is crucial for proper diagnosis and subsequent management. Other choices, while related to dental cysts or lesions, do not align with the specific radiographic findings noted in the question as precisely as primordial cyst does.