Can an abscess above a bridge NOT cause any pain? How can you have an abscess without pain? (photo)

I've had a bridge for 10 years. It's the Upper eye tooth and the one back from the eye tooth. At my last cleaning my dentist said I had an abscess in the hole where the old tooth had been removed. I've NEVER experienced ANY pain. She said I need to have a root canal on my front tooth. She also said my teeth could fall out if I didn't have this root canal.