Hi, Pus is suggestive of infection in the guns below teeth. As u had undergone surgery for your gums 10 years back, may be same the infection has recur. It happens when our body immunity goes down due to other illness. U need to visit an endodontist and get an oral examination done. After oral examination and radiographic examination only we can decide upon the cause and treatment plan for your problem.

Hi there... As u said u noticed pus discharge.. So first of all visit ur dentist n get an x-ray done for this region to find out the exact source of infection.. It could be either because of the same tooth that u got root canal treated or else it could be because of something else(adjacent tooth or just a gum disease) .only after then ur treatment modality would be decided.