A patient with a half-rotted large tooth in the back is a common clinical condition. For this case, a specific analysis of the problem is needed to see where the rotten area is. If the rotten part is mainly located above the gum, most of the cases can be restored according to this tooth body. First of all, the rotten decayed part should be removed, then do the systematic root canal treatment for the pulp of the tooth, after the root canal treatment, apply the way of pile core to drive the pile core into the root canal of the tooth, finally apply the way of crown restoration to repair the whole tooth, and the tooth can continue to serve us for a long time. If the decayed area has penetrated deep into the root of the tooth, sometimes it can not be restored by the restoration method of the tooth alone, so the tooth can only be extracted and restored by the movable denture or fixed denture.