If there is a cavity in the innermost tooth, the position of the tooth should be judged. If it is a functional tooth, which is the second molar, either one should be preserved and should be treated as early as possible to heal the decayed tooth and make it exercise the function of chewing. If the cavity has reached the nerve, root canal treatment should also be performed as soon as possible, and after the treatment, pile crown restoration should be performed to restore the chewing function. If the tooth is the eighth tooth, which has no big chewing relationship, and the position is not very positive, or there are various food embedment and so on, this tooth requires that if there is a cavity, you can choose to extract the treatment to solve the fundamental problem, and prevent the inflammation of the tooth.