The brightness of teeth depends primarily on the surface condition of the enamel.
Smooth enamel naturally reflects light better, giving a smile a bright and radiant appearance. Conversely, when micro-deposits accumulate or the surface becomes more uneven, teeth appear duller.
Coffee, tea, wine, acidic drinks, tobacco, and certain foods gradually contribute to this loss of brightness. Even when teeth are clean, they may appear less bright simply because the enamel surface reflects light less effectively.
Contrary to popular belief, restoring shine doesn't necessarily mean "severely whitening" teeth. The goal is primarily to smooth, polish, and revive the natural luster of the enamel.