Tooth decay is not necessary to kill the nerve, but when the tooth decay is more serious and causes obvious neuropathic pain, that is, when it causes pulpitis, it is usually necessary to kill the nerve. Tooth decay is usually called dental caries, which is a disease caused by the decay and disintegration of the hard tissues of the teeth due to the invasion of bacteria. In the early stage of tooth decay, there is no painful symptom, but only the change of hard tissue, color and texture of the tooth. In the early stage of tooth decay, there is no painful symptom, but only a change in the hard tissue, color and texture of the tooth, which is commonly known as black color, brittle texture and softness of the tooth, which is commonly known as worm tooth or worm cavity. In this case, we should use the power system of dentistry to remove the decayed part of the tooth, and then use the filling material to repair it. In this case, it is not necessary to kill the nerve at all, but only when the tooth decay causes serious tooth pain, then only after killing the nerve and then root canal treatment.