The yellowing of the inside of the teeth may be a normal physiological phenomenon, exogenous coloring, etc. It may also be related to pathological factors such as dental calculus and dental caries. 1. Physiological factors: the enamel of human teeth is transparent, dentin is yellow, resulting in yellowish teeth color, if the inner side of the teeth is yellow may be a normal color, no need to worry too much. 2. Exogenous coloring: such as long-term tea, smoking, drinking carbonated beverages, etc. caused by tea stains, smoke stains, pigmentation spots, etc., can also be manifested as the symptoms of yellowing of the inner side of the teeth, timely and good dental cleaning, the above symptoms can be gradually relieved. 3.Pathological factors (1) Calculus: If the teeth are not cleaned thoroughly, food residues and soft tartar will accumulate in the inner side of the teeth for a long time, which will gradually mineralize into calculus over time, which can be manifested as yellowing of the inner side of the teeth, and may be accompanied by bleeding, redness, swelling and pain of the gums. (2) Caries: Bacterial infection due to inattention to oral hygiene, further dental caries, lesions can be manifested in the inner side of the teeth yellowing symptoms, can be accompanied by pain. If the inner side of the teeth yellowing need to pay attention to oral hygiene, at the same time should be timely consultation, clear diagnosis and active treatment, so as not to delay the condition.