Use a straw to consume staining beverages (such as coffee or tea) to limit their direct contact with the enamel of the front teeth and thereby preserve their whiteness.

noli's read

The underlying physical concept is intuitive: by directing the liquid past the incisors, one limits the deposition of colored pigments on the visible enamel. Furthermore, recommendations from the American Dental Association (ADA - expert opinion) support the use of a straw to minimize contact between staining or acidic beverages and the dental surface. However, rigorous clinical data (such as randomized controlled trials) specifically evaluating the long-term effect of a straw on tooth whiteness remain very limited. An experimental study published in the journal General Dentistry highlights that the effectiveness of this method depends crucially on the position of the straw: it must be placed toward the back of the mouth, because if it is placed just behind the lips, the liquid still bathes the teeth. Moreover, after swallowing, saliva inevitably redistributes residual pigments throughout the mouth. The trick is therefore mechanically logical and validated by professionals, but its effectiveness in daily life depends primarily on how you position the straw.

the sources

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