Porcelain teeth can not be cold light whitening teeth. Because after the restoration of porcelain teeth or all-porcelain crowns, the material characteristics of the teeth determine that the color of the teeth will not change, and generally porcelain teeth and all-porcelain teeth will not appear to turn yellow again. If cold light whitening is performed, the color of the natural teeth may become white, while the color of the restored dentures does not change, thus creating a color difference problem. Therefore, if a patient is going to choose to undergo cold light whitening of teeth and also to have porcelain crown restoration or all-porcelain crown restoration, he or she must undergo cold light whitening first. This way, the color of the teeth will be upgraded to a certain level and then the corresponding porcelain crown or all-porcelain crown will be chosen, so that the final restoration effect is more consistent and the color difference problem can be avoided.