Generally the time of complete destruction of teeth by tooth decay is related to the oral hygiene condition of the patient and the hardness of the teeth. Tooth decay, also known as caries, is a disease of the hard tissues of the teeth, caused by bacteria acting on the teeth and destroying the tooth tissues to form cavities. Once the cavity appears, it should be treated in time, otherwise, the bacteria will destroy the tooth more seriously. From the initial superficial caries, the medium caries develops into deep caries, and if it destroys the pulp tissue, it will form pulpitis or periapical inflammation. If the tooth continues to be destroyed, then the whole tooth will be decayed, and also forms the residual root or crown, and such a tooth can only be extracted. Caries is the most common dental disease in the oral cavity, for caries must do early diagnosis, early treatment, in the early stage to control the caries, so that it does not continue to develop, so as not to cause more serious consequences. We should go to the hospital regularly for examination, and once we find the appearance of worm teeth, we should treat it in time, so that we can control the tooth decay and make it not develop further. If not treated in time, tooth decay will not stop and will keep damaging the teeth, which is very detrimental to oral health. Therefore, we must pay attention to the health of our teeth, and we must treat tooth decay in time.