Which classification of stains occurs within the tooth structure and is not removable by coronal polishing?

Intrinsic stains are classified as those that occur within the tooth structure itself, resulting from various factors such as developmental disturbances, aging, or certain medical conditions, including exposure to certain medications. Because these stains are embedded within the enamel or dentin, they cannot be removed by coronal polishing, which primarily affects only the outer layers of the tooth surface.

In contrast, extrinsic stains are located on the surface of the teeth and are often caused by dietary factors, habits like smoking, or the use of certain oral care products. These stains can be removed through coronal polishing techniques. Similarly, exogenous stains originate from external sources, which means they can also be removed when addressing the external tooth surface. Endogenous stains, while they occur internally, usually refer to stains formed during tooth development and do not necessarily differentiate in context from intrinsic. Intrinsic stains remain the clear answer as they highlight the inability of coronal polishing to affect stains located below the surface of the enamel.