The difference between tooth pigmentation and tooth decay is as follows, long-term tea and coffee drinking or smoking will cause pigmentation on the surface of tooth lip and tongue and sulcus point gap etc., untimely hygiene cleaning and frequent food embedment will cause the occurrence of cavity, shallow caries is chalky, deep caries is dark brown. X ray shows that there is no difference between the density of pigmented area and surrounding area, the density of cavity is low, there is no abnormal reaction in the pigmented area when the tooth is stimulated by cold, heat, acid, sweet, etc., and the cavity will produce obvious soreness.