Which type of stain cannot be removed through the polishing process?

Metallic stains cannot be removed through the polishing process primarily because they originate from the incorporation of metal ions into the tooth structure itself, making them an intrinsic part of the tooth enamel or dentin. These stains often occur from exposure to certain medications or heavy metal deposits, which alter the color and composition of the tooth rather than just settling on the surface.

Polishing is effective for removing extrinsic stains, which are surface stains caused by food, drink, or tobacco and can generally be eliminated with abrasive agents. Surface stains reside outside the enamel and do not penetrate the tooth structure, making them more susceptible to polishing techniques.

Intrinsic stains, while more challenging than extrinsic stains, may sometimes be treated through whitening methods that can penetrate the enamel. However, metallic stains, by nature of their deeper incorporation into the tooth, remain unaffected by standard polishing procedures and typically require more advanced dental treatments, such as bleaching or restorations, to address their appearance.