To judge whether the tooth is rotten to the nerve is to judge whether the caries has invaded to the nerve, clinically there are the following methods: 1.consultation for the patient’s symptoms, the early stage of caries development will only have the change of tooth color and texture, which will not cause pain. But once the caries causes pain, especially spontaneous pain, it means the caries has developed to the nerve, because there are painful symptoms; 2, the auxiliary judgment method is dental film examination, dental film can be viewed through imaging to the corresponding location of low density shadow. If the low density shadow has invaded to the pulp cavity, it means the tooth has been decayed and invaded to the nerve part, which is also a better way for clinical examination.