How do stains typically occur on teeth?

Stains on teeth primarily occur by adhering to the surface directly. This can happen through various means, such as the consumption of certain foods and beverages, like coffee, tea, red wine, and various fruits. These substances can leave pigments that settle on the tooth enamel and cause discoloration. Additionally, tobacco products can contribute to surface stains on teeth, further emphasizing the importance of hygiene practices in dental care.

While other factors may influence tooth appearance, the direct adherence of particles and pigments onto the tooth surface is the primary mechanism for staining. It's also important to consider that stains can be classified as extrinsic or intrinsic. Extrinsic stains are those that attach to the exterior surface of the teeth, whereas intrinsic stains originate from within the tooth structure. However, for the purpose of this question and the options provided, the correct answer focuses on the direct adherence of staining agents to the tooth surface itself.