Which stain is characterized as being tenacious and hard to remove?

The stain characterized as tenacious and hard to remove is the tobacco stain. Tobacco stains occur when tar and nicotine from smoking or chewing tobacco accumulate on the surfaces of teeth. These stains are notoriously stubborn due to their composition, which allows them to adhere firmly to the enamel and sometimes penetrate into the dentin, making them difficult to eliminate through regular brushing or over-the-counter whitening products. Professional dental cleaning is often required to effectively remove such stains, highlighting their tenacity.

In contrast, other stain types like green, yellow, and black line stains generally do not exhibit the same level of persistence. Green stains, often associated with poor oral hygiene or dietary factors, are typically easier to remove. Yellow stains can result from dietary choices such as consuming coffee or tea, and are usually manageable with routine dental care. Black line stains are mineralized deposits that can be somewhat resistant, but they still usually respond well to professional cleaning methods. Thus, tobacco stains stand out due to their difficult removal properties.