The reasons why teeth still hurt after root canal treatment are: 1. the presence of missed root canals and inflammation of the residual pulp, causing pain. 2. the formation of root canal lateral penetration during root canal preparation, resulting in bacterial infection causing swelling and pain. 3. when the hydrogen peroxide solution is pressurized to flush the root canal, the gas produced escapes the apical hole causing swelling and pain. 4. instruments penetrate the apical hole, damaging the periapical tissue or root canal paste, gum tip, etc. beyond the apical area, causing irritation and pain. 5. 5.Fillings or restorations on the coincidental surface, with occlusal high points, cause early contact or coincidental interference, resulting in chewing pain. 6.The tooth forms a hidden fracture or longitudinal fracture, producing pain during occlusal contact.