What are stains that cannot be removed from the surfaces of the teeth by coronal polishing?

Intrinsic stains are those that originate from within the tooth itself and cannot be removed through coronal polishing, which is designed to clean the outer surfaces of teeth. These stains can be caused by various factors such as developmental conditions, fluorosis, certain medications taken during tooth development, or trauma to a tooth.

Such stains differ from extrinsic stains, which are surface stains that can typically be removed through polishing or professional cleanings. Endogenous stains refer specifically to those that arise from within the tooth structure, aligning closely with the concept of intrinsic stains. Transient stains may appear temporarily due to dietary choices or other external factors and can usually be removed through good oral hygiene and professional cleaning.

Thus, intrinsic stains are the stains that are resistant to removal by coronal polishing, making them the correct answer in the context of this question.