Whitening involves applying bleach solutions to the teeth. The bleach attacks the highly colored organic molecules that lodge between the crystals of tooth enamel (the outermost tooth covering) or in the dentin (the tooth material under the enamel). It’s these organic particles that give the teeth a stained appearance. For surface stains, the solution is left on the teeth usually for 30 minutes to one hour, depending on the method used. For internal stains on non-living teeth that have had root canal work, the bleach might be sealed inside the tooth. The bleaching process continues until these organic particles are rendered colorless. Bleaching works best on yellowish stains and even some brown stains, but may not work at all on gray discoloration. It’s important to keep in mind that bonding material and fillings cannot be whitened with bleach. If you have these restorations in your mouth, you should consider how your teeth will look if the natural parts become whiter and the bonding stays the same.