The causes of toothache due to hot and cold stimulation after filling are as follows: 1.The acid etchant is not completely removed during the filling process, and the residual part penetrates into the tooth tissue and provokes the pulp to cause allergic reaction. 2.The depth of the cavity is close to the pulp, and the cavity is not cushioned at the bottom, so the cold and hot stimulation will be transmitted to the pulp along the filling to provoke the pulp and produce soreness. 3.If the filling is silver amalgam, the cold and heat conduction speed is faster, and it needs to be replaced by glass ionomer cement, composite resin, etc. to relieve the pain. The pain can only be relieved by replacing the filling with glass ionomer, composite resin, etc. 4. The chemicals released by the filling material will stimulate the dentin tissue and form restorative dentin before the symptoms disappear.