Cavity toothache occurs when bacteria infect the hard tissue of the tooth, approaching or reaching the dental nerve, causing a pain response from the nerve, which is also a self-protective reaction. Initial treatment for cavity toothache involves using a drill to remove the decayed hard tissue of the tooth. If the decay is completely removed and the dental nerve is not exposed, this condition can be directly treated by filling or using a pulp-capping agent to protect the nerve before filling. If, after removing the decay, the dental nerve is exposed or reached, the situation cannot be resolved with a direct and immediate filling. Instead, nerve-killing procedures are necessary, which involve root canal treatment of the tooth.