I would consult with your endodontist and see what they say. They opened the tooth and saw what was going on inside. Your general dentist can do that also. If there's extensive decay in that tooth still or there's some reason to believe the bridge is bad, then replacing it would be ideal. If the decay isn't bad and the bridge seems fine, then placing a filling in there would work as well. Root canals are done when there's a problem in the pulp but it doesn't necessarily mean that it was due to a cavity. Its possible for the pulp to gradually degenerate over time due to the trauma from dental treatment and the injury caused by the original cavity.
The endodontist generally do root canals and let the dentists finish the restorative aspect of the treatment. Usually they'll restore the tooth at the request of the dentist but usually leave that aspect up to the dentist. They usually just limited their practice to root canals and other associated treatments.
It can happen with decay occurring underneath the crown or bridge work.
Thanks again for your help and quick resonse Dr. T.
Thank you very much for the quick response. Good advise to check with the endodontist. Follow up question. Why would the endodontist not discuss this with me at the time the treatment was completed. Would it not have made sense for him to do the filling at that time, if it was the best option? Also, my dentist suggests that the reason for doing a new bridge is due to the infection still being under the bridge, which will eventually lead to a reinfection, unless the bridge is replaced. I don't understand how the tooth would have extensive decay, as it has been covered by the bridge for the past 6 years. Is it common for decay to develop under the bridgework on the stumped supporting teeth? I also have an opposing gold bridge on the lower right side that is over 25 years old now. No similar problems to date, touch wood. Although, my dentist has also suggested this one needs to be replaced. Any furhter clarity is appreciated.
Again, thank you very much for taking the time to respond to by situation!