What happens to stains that are incorporated into the tooth structure?

Stains that are incorporated into the tooth structure undergo a process where they become intrinsic, meaning they become part of the tooth enamel or dentin rather than being merely surface-level deposits. These intrinsic stains can result from various factors such as certain medications taken during tooth development, excessive fluoride, or even factors like trauma to the tooth.

Once a stain becomes intrinsic, it embeds itself within the tooth structure and cannot be removed by standard cleaning or whitening procedures, which typically target only extrinsic stains (those on the surface). Treatments aimed at removing intrinsic stains often involve more intensive dental procedures, such as veneers or crowns, since the stain is now a permanent alteration of the tooth's internal structure.

In contrast, superficial stains remain on the enamel's outer layer and can usually be removed through professional cleaning or polishing. While fluoride can help strengthen teeth and prevent decay, it does not remove intrinsic stains. Furthermore, while intrinsic discoloration can affect aesthetics, it does not inherently lead to decay, as decay is typically caused by bacteria and other factors rather than being directly linked to the presence of stains. Therefore, the accurate depiction of intrinsic stains is that they cannot be removed, which aligns with the correct answer.