How do you clean beneath a fixed bridge without irritating the gumline?

With a fixed dental bridge, what’s the best way to remove plaque where it meets the gums without making tender or bleeding tissue worse? The design seems to matter: is there space underneath for a floss threader or an interdental brush, and how can you tell that a tool passes comfortably without forcing it?

I’d also like to understand the difference between occasional bleeding during cleaning and bleeding or irritation that persists or gets worse. When would that be a reason to book a dental assessment rather than just adjust the cleaning technique?