Tooth yellowing can be roughly divided into two types, one is that the pigment outside sticks to the teeth, which leads to yellow teeth, and the other is that the teeth themselves are yellow. These typical teeth are dental fluorosis and tetracycline. The first reason for yellowing is relatively simple. Just wash your teeth. The second is more complicated. Common whitening methods include bleaching, porcelain teeth cosmetic repair and resin repair. Bleaching lasts for a relatively short time and will gradually return to its original color.