If there is tooth decay, the tooth still has painful symptoms after filling. There are several causes as follows: the first one is that the tooth has secondary decay. In this case, the pain of hot and cold stimulation usually occurs after a long time after the filling, and the X-ray film can be taken to see the formation of decay under the filling again, and it needs to be re-repaired at this time. The second type is the irritation of the filling material to the tooth pulp. If the decay is deeper and closer to the pulp, the filling needs to be cushioned in the cavity, sometimes there is no cushion or the filling is directly applied with glass ionomer or photosensitive resin, these two materials can directly stimulate the pulp and cause pain to the pulp. In this case, the filling material should be removed, re-bedding and refilling treatment. The third type is that the doctor misjudged the disease before filling, and it may have developed into pulp congestion or chronic pulpitis, but the doctor only treated it as caries for repair, after filling, the bacteria still exist inside the pulp, and the pain will still be intense, then root canal treatment is needed.