Recently, many patients have asked about teeth whitening, and the same question has different answers because everyone’s situation is different, so there is no way to answer in the same way. It just so happens that a friend on the website consulted me about a similar problem, and here I give an appropriate answer based on my knowledge of teeth whitening, and I hope you will pat me on the back if there is anything wrong. First of all, let’s introduce the common causes of tooth staining. Dental fluorosis Fluorosis, also known as dental fluorosis or enamel fluorosis, is a typical endemic disease with regional characteristics, and is the most common and prominent symptom in the early stages of chronic fluorosis. Fluorine mainly damages the enamel-forming cells of the tooth embryo during enamel development, therefore, excessive fluorine can only enter the organism during the mineralization period of tooth development for dental fluorosis to occur. If, before the age of 6 or 7, the patient lives in an endemic area with high fluoride content in drinking water for a long time, even if he moves to another place later, he cannot avoid the involvement of permanent teeth that will erupt later; on the contrary, if he moves to a high fluoride area after the age of 7, he will not develop dental fluorosis. Clinically, fluorosis is often divided into three types according to the degree of enamel lesions. Chalky (mild): the tooth surface loses its normal luster and appears opaque plaque; discolored (moderate): the tooth surface appears yellow, yellow-brown or brown; defective (severe): in addition to the above changes, the tooth surface also appears shallow sockets or pit-like defects, or the tooth loses its normal shape due to wear.