So what? The following is the consultation of netizens. User consultation: doctor, I recently found that the lower part of the teeth is black and the surface is a little yellow. I feel very distressed. May I ask? Thank you? First of all, let's understand the reason why the teeth are yellow: the top grade is smoking, and the yellow substance in tobacco adheres to the teeth. The second type is tetracycline teeth, which is caused by frequent use of tetracycline as a child. It combines with calcium in the body to form a yellow compound of tetracycline calcium, which is deposited on the crown of teeth. The third kind is mottled enamel teeth, also called dental fluorosis, which is caused by the high concentration of fluorine in drinking water. When the concentration of fluorine exceeds one millionth, it will affect the calcification process of tooth germ, and the tooth surface will be yellow and uneven, with punctate or strip-shaped concave defects. When teeth calcify before the age of 5, mottled enamel teeth often appear. Teeth are black and yellow. To sum up, about? Recommended by vibrant dental experts in Meilai Shenzhen Plastic Surgery Hospital-Cold light whitening teeth. Meilai Vitality Stomatologist said: Cold light whitening is an excellent method for tooth whitening at present, which is suitable for mild to moderate tetracycline teeth. Clinically, cold light whitening is effective not only for tetracycline teeth, but also for drug-induced discolored teeth and exogenous pigment teeth (such as drinking strong tea and coffee for a long time). At the same time, the cold light whitening technology uses light energy to uniformly act on the tooth surface, which is contrary to the pigment selectivity in the teeth of the studio. Swallowing the pigment growing on your teeth slowly can completely remove the bad pigment on your teeth and make your teeth white and flawless from now on. The whole treatment process is painless. It is a real tooth whitening technology. And the effect is lasting. The above is the relevant introduction, and I believe you will know something through the introduction of the above experts.