Root canal treatment of teeth can be uncomfortable and not painful. Root canal treatment of teeth is a routine treatment for pulpitis or apical inflammation. First, the nerve is inflamed or necrotic and has no retention value and the infected pulp tissue needs to be removed. In the case of pulpitis, the nerve is partially viable and there will be significant pain, and pulp extraction under local anesthesia can be performed, which is only a painful pinprick reaction. After pulp extraction, root canal preparation is performed to remove the infected bone with a file, followed by root canal disinfection. There may be discomfort after the root canal is sealed. This is because the root canal preparation process may push the infected material outside the root canal, or the root canal sealant may irritate the apical region, causing a painful reaction in the apical region. After the inflammation of the root canal is controlled, a tight root canal filling will be performed. During the root canal filling process, there is a pressure on the apical region and a swelling sensation occurs. Sometimes the root canal filling material is pushed out of the apical hole, causing pain in the apical area, which usually resolves on its own in two or three days. In case of a perfect root canal treatment, there will be no significant pain during the treatment. Therefore, there is usually no pain during the root canal treatment, and there may be a short period of swelling and pain.