Which of the following is classified as an intrinsic stain?

An intrinsic stain originates from within the tooth structure, often linked to factors such as genetics, dental trauma, or certain medications taken during tooth development. The black line stain, which is a type of intrinsic stain, is typically associated with the accumulation of iron in the saliva, leading to the formation of a darkly pigmented line along the gingival margin. Unlike extrinsic stains, which are caused by external factors and can usually be removed through professional cleaning and good oral hygiene practices, intrinsic stains affect the tooth's internal composition and may require more complex treatments for remediation.

Other types of stains mentioned, such as those from red wine consumption or smoking-related discoloration, are examples of extrinsic stains. These forms of discoloration occur on the surface of the teeth and can usually be addressed more easily through regular dental cleaning or whitening procedures. In contrast, dental caries is the result of decay and does not fall into the category of staining but rather represents damage and decay within the tooth structure.