What type of stains cannot be removed from the surface of the teeth?

Intrinsic stains are discolorations that occur within the tooth structure itself and are typically more challenging to remove than other types of stains. They can result from factors such as excessive fluoride exposure during tooth development, tetracycline use, or trauma to the teeth, leading to changes in the internal structure and coloration of the enamel and dentin. Because intrinsic stains are incorporated into the tooth, they often require more advanced whitening procedures, such as professional bleaching or restorative treatments, to address.

This distinguishes them from extrinsic stains, which are formed on the outer surface of the teeth due to external factors like food, drinks, and tobacco, and can often be removed through regular dental cleanings or at-home whitening products. Transient stains and surface stains generally refer to temporary or more superficial discolorations that are usually easily treated. Therefore, intrinsic stains are the type that cannot be removed through standard cleaning practices, making this the correct response.