Fillings can be painful and are related to the depth of tooth decay. Tooth filling is to remove the decayed hard tissues and then to fill the tooth. While removing the decayed hard tissues, it also generates a certain pressure of drilling and grinding on the pulp tissues, and the nerve of the tooth will have a certain reaction. If the tooth decay is shallow and far from the nerve, there will be no obvious pain during the drilling process, but there may be mild discomfort. If the tooth decay is deeper and closer to the nerve, there will be obvious pain during the drilling process. There will also be varying degrees of pain after the filling. If a small pulp hole is not detected during the filling process, there will be significant pain after the filling, which is very intense and sometimes radiates to the ipsilateral head and neck, and it is difficult to distinguish which tooth has the pain. Or the filling material may be too high during the filling process to form an occlusal trauma, causing pain in the apical region. Or the filling material does not restore the contact point of the adjacent surface well, and the overhang will also cause the pain of the tooth. So the filling will have obvious pain if the tooth decay is deeper or the filling material is too high after filling. If the pain is obvious, the filling treatment can also be considered under local anesthesia.