Tooth decay with only a residual root is a relatively common clinical situation. In this case, there are several treatment options as follows: firstly, if the remaining root is too small, you can consider extracting the root and then restoring it with implant or removable denture, which is one of the methods. If the root is long enough and very strong, then the tooth can be restored by means of a crown. Specifically, you can do systematic root canal treatment on the pulp of the residual root, then drive a pile on the residual root, and then make a porcelain crown on the pile for restoration. This restoration method is relatively less damaging and effective, but requires the patient to have a good condition of the residual root.