A dental radiograph shows a well-defined radiopaque spot in the posterior maxillary region. What is the most likely diagnosis?

A radiopaque finding on a radiograph indicates the presence of a material that blocks x-ray transmission. In the posterior maxillary region, a well-defined radiopaque spot is most likely a foreign body (such as a broken root canal instrument, metallic fragment, dental material, or displaced restoration). Amalgam tattoos are clinical soft-tissue lesions; while amalgam particles can appear radiopaque in soft tissue radiographically, when described as a 'spot in the posterior maxillary region' on a dental radiograph, foreign body is the most appropriate answer. A blue nevus is a soft tissue pigmented lesion, not visible on x-ray. An osteoma would be diffuse and within bone.