The medical name of tooth decay is dental caries, and the possible reasons for the pain of dental caries after filling and repairing are pulpal hemorrhage, pulpitis, moderate caries and deep caries filling without cushioning, etc. The details are as follows. 1. Pulp congestion: the process of cavity preparation may produce physical stimulation to the pulp, continuous drilling and grinding of heat and negative pressure generated by drilling and grinding can stimulate the pulp, causing pulp congestion. 2. Pulpitis: If the pulp is not treated by endodontic treatment due to wrong judgment of the pulp condition, the pulp inflammation will persist and cause tooth pain. 3. Medium and deep caries filling without cushioning: amalgam direct filling can conduct cold and hot stimulation, composite resin direct filling can cause chemical stimulation to the pulp, causing pulp congestion. There may be other reasons why you still feel pain when you encounter cold water after filling and repairing caries, so it is recommended that you go to the hospital in time to get a clear understanding of the cause of the disease and then carry out targeted treatment.