If a tooth has a cavity and the inside is black, it may be caries or pulpitis. If it is caries to be filled, if the caries is very shallow, generally can not be anesthesia, the treatment process will have a slight sense of acidity, most people can withstand. If the caries is deeper, near the pulp, cleaning process will have more obvious pain, then you need to take means to avoid pain, called painless treatment. Currently, local anesthesia or laughing gas sedation is used. Modern anesthesia can be basically painless, because the doctor will be applied in the surgical area of the mucosal surface anesthesia cream, and then injected with painless local anesthesia instrument anesthesia. The injection needle used in the painless local anesthesia machine is very fine, and together with the surface anesthesia previously administered, there is no pain when puncturing the mucosa. Under microcomputer control, the anesthetic will be injected slowly and evenly into the surgical area, the whole process will last several minutes. Such a set of procedures can be completely painless, and for those who are extremely fearful, the doctor can also use laughing gas to sedate them. Child patients can be treated under general anesthesia, anesthesia will take effect within an hour, the anesthesia area will have a numbness and swelling, the whole process of treatment will not feel pain, the doctor will also try to divert the patient’s attention during the operation to ease the nervousness, in order to get a better therapeutic experience.