The more you brush your teeth, the yellower they become. This can be caused by improper diet, tetracycline and pulp necrosis. 1. Improper diet: often drink tea, coffee, etc., will cause darker pigment residue on the teeth, which will lead to the phenomenon of the teeth becoming more and more yellow when brushing. 2. Tetracycline teeth: when patients consume too much tetracycline drugs during the period of tooth development or mineralization, it will lead to more and more yellow teeth. 3. Pulp necrosis: there are individual teeth due to pulp necrosis, the tooth lack of nutrients and the resulting crown discoloration, so that the teeth become more and more yellow. When the phenomenon of yellow teeth, it is recommended that patients go to the regular hospital stomatology to find out the cause of the disease in a timely manner, and according to the cause of the treatment, in ordinary life to develop good oral habits.