Why does a tooth still hurt after the nerve has been killed?

Pain may still occur after a tooth nerve has been killed, mainly due to the following reasons: 1. Inflammation of residual pulp: During the process of killing the tooth nerve, it may not be possible to completely remove all pulp tissue, leading to inflammation of remaining pulp tissue and subsequent pain. 2. Apical periodontitis: After the tooth nerve has been killed, inflammation around the root tip may not have fully subsided, resulting in apical periodontitis and causing pain. 3. Root fracture: Teeth may develop cracks due to external forces or long-term wear. These cracks can damage the nerves and blood vessels inside the tooth, resulting in pain. 4. Enamel irritation: After the tooth nerve has been killed, the enamel may become more sensitive. When the tooth is exposed to stimuli such as hot or cold, acidic or sweet substances, the enamel may no longer effectively protect the inner nerves of the tooth, leading to pain. If you encounter such situations, it is recommended to seek timely medical attention to identify the cause of the pain and receive targeted treatment.