Drinking hot water for toothache and cold water for painless toothache is caused by septic pulpitis, which is a phenomenon of heat expansion and cold contraction due to the inflammation of the nerve in the tooth and the production of pus. When drinking hot water, the pus cannot be discharged, which tends to produce pain in the tooth, while cold water tends to produce the gathering and shrinking of pus, which is then able to relieve the pain. In this case, root canal treatment is usually required to remove the inflamed nerve and to remove the infected contents, remove the pus, and seal the medicine in the root canal. After the inflammation of the tooth has subsided, the tooth will be filled, the filling will be tightly closed, and then the root canal treatment will be done, and then the tooth will be restored with porcelain braces to ensure that the tooth is resistant to fracture and that no more secondary caries will occur, and to avoid grinding other affected teeth.