Tooth calcification includes two stages of physiological and pathological, as follows: 1.Physiological calcification: It refers to the completion of crown and root morphology during tooth development, and the increase of calcium ions in the hard tissues of teeth, which increases the hardness of teeth. After the tooth erupts, if the surface is often adhered to food residue and soft scale, the acid produced by the decomposition of bacteria can demineralize the tooth tissue, and the structure is loosened, and then form caries. 2.Pathological calcification: It refers to the heavy abrasion of tooth surface, and the pulp forms into dentin cells under the chronic stimulation, which causes the pulp cavity to be occluded and narrowed, and at the same time the root canal wall is gradually thickened, resulting in the root canal narrowing and inaccessibility.