Much of the interpretation of this point rests with experience, and learning by mistakes. However, we do use rough rules of thumb, such as the dentin and pulp in teeth. If it is whiter than the pulp, it is considered radiopaque, and if it is darker than dentin it is radiolucent. In bone, if a lesion shows up as darker than the bony trabeculae, it is considered radiolucent. If it shows as whiter than the trabeculae it is considered radiopaque.
Some lesions contain both radiopaque and radiolucent structures.
Interpretation of radiolucency and radiopacity is general and imprecise. This makes the hole in the bone less dense than the surrounding bone, thus radiolucent. The destroyed bone may or may not be in the process of being replaced by a less dense tissue such as granulation tissue or neoplastic tissue. Radiopaque lesions indicate that a substance more dense than the surrounding bone is being or has been laid down. Sometimes this denser material is harder, more calcified bone, but it also may be very dense, fibrous connective tissue with or without calcification, or perhaps a denser but inferior bone.