The constant vague pain after removing the nerve of the tooth by root canal treatment may be caused by the normal pain reaction after the operation, medication pain, tooth splitting and so on. 1. Normal postoperative pain reaction: it is because when root canal treatment is carried out, it will cause some wear and tear on the tooth body, which will have some effect on the sensitive tooth, and there will be a certain degree of pain, but it will usually disappear on its own. 2. Pharmacological pain: When root canal treatment is carried out, root canal cleaning and sealing disinfection will be carried out. For the root canal disinfectants commonly used in the clinic, some patients will have obvious reaction and painful feeling. 3. Tooth splitting: after root canal treatment, if the tooth cannot be restored with crown in time, the tooth will be split and pain will also occur. If the symptom of constant hidden pain after removing the nerve of the tooth by root canal therapy persists without relief, you need to seek medical treatment in time.