Hi sir...    The decaying and pain is due to reinfection of root canal treated tooth... You need to take x_ray(IOPA) of the concerned tooth .. If reinfection is there you need to do Re_Rct of the tooth and then do capping.. Failure to put cap may cause spread of infection..so it is mandatory to put crowning of root caal treated tooth

Your root canal treated tooth may get infected. You may need of re-rct.

Hloo Sir May be due to reinvention of root there might be pain You need to get x ray done to get the present status of your teeth You can also practo consult us Regards

Get an X-ray done. If it is a reinfection and the tooth can be restored then you can opt for retreatment. However if the tooth cannot be restored then you may have to extract it and think of a replacement like an implant or a fixed bridge