The reasons for yellowing of tooth color are as follows: 1. Frequent chewing of hard textured food can lead to heavy abrasion of teeth, disappearance of transparent enamel and exposure of yellow dentin, making the tooth surface yellow. 2. Not paying attention to oral hygiene and cleaning, often eating food with high viscosity, the tooth surface will deposit a large amount of food residue and soft scale, covering the original color of the teeth, making the teeth yellow, accompanied by bad breath. 3, Long-term smoking, tea, coffee, etc., smoke, tea stains, coffee stains and other pigments can adhere to the tooth surface, making the teeth yellow or black, accompanied by swollen gums, bleeding. 4, root canal treatment of teeth or chronic pulp necrosis of teeth, will lose the nutrients of the pulp tissue, the tooth color gradually becomes dark yellow, brittle texture, easy to crumble and fracture.