The back of the teeth yellow, if for the whole piece of foreign material attached to the tooth surface, can be removed by ultrasound is usually tartar, may also be abnormal tooth development or tetracycline teeth. 1. Tartar. Normal teeth are milky white or yellowish, the specific color shades vary from person to person, as a natural physiological manifestation, but if there are abnormal attachments on the tooth surface, can be removed by instruments such as scaling and scraping, often due to poor maintenance of oral hygiene, and the attachment of tartar on the tooth surface. 2. Abnormal tooth development, tetracycline teeth. The back of the teeth may be yellow for enamel development abnormalities, periodontitis damage to the permanent tooth embryo during the period of milk teeth, may cause different degrees of enamel defects, yellowing, but also in early childhood taking tetracycline caused by yellowing of the teeth inside. The back of the teeth is yellow, whether it is calculus specific to the hospital based on oral examination and medical history to determine.