Use a straw when consuming colored drinks (such as coffee) to limit their direct contact with the front teeth and thereby preserve their whiteness.

noli's read

Drinking through a straw to reduce the direct contact of colored beverages with the front teeth is based on validated physical logic. A comparative clinical imaging study, published in the British Dental Journal, confirmed that using a straw significantly reduces the contact time of liquids with the front teeth. Nevertheless, for this to be truly effective, the study specifies that the straw must be positioned very far back in the mouth, a habit that is uncommon in daily life. The Canadian Dental Association, through Dr. Euan Swan (expert opinion), also tempers this tip by noting that the back teeth remain exposed to the staining agents. Finally, the tongue, coated with pigments, naturally ends up redistributing these coloring agents across the entire smile when one swallows.

the sources

No named source held this one up — that absence is part of the verdict.