The reasons why the child’s tooth still hurts after filling include the following points: First, the enamel hidden crack: in the process of decay and cavity preparation, the sharp car needle cuts the tooth tissue, which may cause the weak enamel to occur hidden crack, and the external stimulus can be transmitted to the pulp along the crack to produce pain. Second, the cavity is deeper: when the deeper cavity extends to the dentin layer, if there is no cushion, cold, hot, acid and sweet will provoke the pulp to cause pain. Third, bacterial infection: If the cavity is deeper and the pulp has been infected by bacteria, without root canal treatment in time, the direct filling will cause severe swelling and pain. Fourth, pulp penetration: If accidental pulp penetration occurs during the preparation of cavity type and pulp capping is not performed in time, it can lead to continuous pulp congestion and swelling and produce sharp pain, and root canal treatment must be taken after grinding out the filling to relieve the pain.