If the root canal treatment is performed with right protocols, it should be asymptomatic . If u still experience pain in the respective tooth , it can be due many reasons. Few as follows, Trauma from occlusion May be one of the reason , there might be high point or crown might be placed at an higher level than ideal occlusal level. Incomplete root canal therapy, may any of the canals not attended , or over obturation means root canal at the apex of the root is over filled, or poor sterilisation/ Asepsis , broken instrument in the canal while doing root canal (bio mechanical) preparation means while cleansing and shaping the canals there’s a instrument breakage and its left behind, and infection still persists . Or furcation involvement means the bifurcation area between the roots is involved which leads secondary infection , laceration Of root canal. Even the prognosis of the root canal treatment depends on the diagnosis and treatment plan , and if any contra indications have been committed by the clinician always play a role in failure . Many more reasons do play a role for failure Of Root canal treatment . U need to get an x ray done for right opinion . Go for an OPG (orthopantomogram ) , u can get it done from nearby diagnostic centre which may cost less than RS 500 and take a second opinion from dentist nearby . I tried my best to give my opinion with little data what u furnished. Thank u . Stay Healthy . Good luck . Dr Vinay Sirigere Apple Dental.