If the tooth is badly decayed and there is pain, it is necessary to seek medical attention in time. Usually, if the decay is big and the pain has appeared, it means the infection of decay has reached the pulp, and after the tooth has pulpitis, you should go to the hospital for root canal treatment, using the root canal treatment method to completely remove the infected nerve, control the infection in the root canal cavity, prevent the further spread of the inflammation, so as to relieve the pain. Root canal treatment usually takes 2-3 follow-up visits to complete the treatment, and it takes about 1 month to complete the whole course of treatment. A rotten tooth may also be suffering from periapical infection. The apical periodontitis is caused by the inflammation staying too long and spreading to the periapical area, the treatment also requires dental root canal treatment, after the root canal treatment of the tooth, it is recommended that the crown is protected with porcelain crowns or full porcelain crowns, otherwise the tooth is easy to bite split, bite crack.