The toothache of drinking water after one year of root canal treatment is considered to be related to factors such as apical periodontitis, gingivitis and pulpitis. 1. Periapical periodontitis: If there is no crown restoration after root canal treatment, it may cause bacteria to enter the apical foramen, leading to the emergence of corresponding inflammatory diseases at the root tip, such as periapical periodontitis, which will cause toothache when drinking water, and will affect normal chewing. 2. Gingivitis: related to the lack of attention to local hygiene after root canal treatment, repeated inflammatory stimulation, resulting in redness, swelling and pus at the root of the gums, can cause gingivitis, resulting in drinking toothache. 3. Residual pulpitis: Root canal treatment clears the necrotic pulp tissue, but the root canal is very complex, if there is residual pulp is not cleaned up, it can cause residual pulpitis. It will cause the patient to have toothache from drinking water or pain from hot and cold stimulation. One year after the root canal treatment, it is necessary to go to the hospital for review to know the recovery situation, and for those who have not recovered well, it is necessary to adjust the treatment program in time.