A lasting white smile depends on knowing why teeth lose brightness in the first place. Surface stains often come from coffee, tea, red wine & tobacco, while some darker changes come from inside the tooth & may not respond the same way to over-the-counter products. The American Dental Association notes that whitening can help with both extrinsic & intrinsic discoloration, but not every product works equally well for every type of stain & restorations such as fillings or crowns do not whiten like natural teeth. That is why smile brightening should begin with the right diagnosis, not guesswork.