Dentist found some decay under crown that hold a permanent bridge. He wants to extract that particular. Any suggestions?

Follow the guidance of your dentist.  If there is decay u see one of the anchor teeth that bridge is no longer salvageable.  Your options are to extract that tooth and:1.  Place two implants and crowns.  This is the best option if there is sufficient bone present.2.  Do a new longer span bridge replacing both teeth ( not my favorite choice, but is an option) to replace. Good luck.

I agree with the answers below. If the bridge is loose it's probably because the tooth with the cavity is broken and does need to be redone.The bridge is not salvageable if it's only being 'held up' by one end. The tooth that is holding the bridge in place will eventually break if it doesn't already have irreparable damage.The options would be to do implants, or another bridge, or partial. The implants are the better option, or even the partial. If you do a big bridge, it will eventually fail so keep that in mind!

It is impossible to answer your question specifically without an x-ray. If the tooth under the bridge is extremely decayed it may not be able to be salvaged. Sometimes it is possible to do a root canal and save the tooth, but not if it is extremely decayed. You will be better served by having one or two implants placed in this area and restoring them.