For shallow caries and medium caries, there is usually no pain after filling, while for deep caries, there will be a short period of pain after filling, which will recover after a day or two, so that the tooth can continue to be used. If there is serious spontaneous pain after filling, then it may be the inflammation of the tooth nerve, and root canal treatment is needed. Tooth filling is the best method to treat the caries, and generally you should get a tooth filling in time when you have caries. If the caries is not treated in time, the decayed tissue will destroy the tooth and damage the pulp, which will lead to pulpitis or periapical inflammation, then the tooth cannot be filled directly, and root canal treatment is needed first, and then the tooth is filled. Once the caries has progressed to deep caries, the nerve must be protected first. If the nerve is damaged, there will be obvious spontaneous pain. If the pain is particularly severe, then the filling material should be removed and then the tooth should be treated with a nerve-killing root canal. Therefore, for caries, it is necessary to do early diagnosis and early treatment, so that the carious tissue can be controlled at the early stage of caries so that it will not continue to develop, and the occurrence of pulpitis and periapical inflammation will be prevented.