1 of 5 dental implants in lower arch is loose, and can't be connected to bridge, is it safe to leave it in the mouth? (Photo)

It is never a good idea to keep a "loose" implant in the mouth. If the implant is truly loose, it needs to come out. It should be relatively simple to replace this implant with a new one. However, if there is just some bone loss around it and it is still immobile, the implant can be disinfected and monitored to see if it can still be used as an anchor.

Hi:If the implant is not infected and if it can be retrieved and taken out  at any time by removing the all on 4.bridge, there is no harm in leaving it in there to see if it tightens up.  Best,Dr. Maddahi

Hi and thank you for your question. The answer to your question is no, it is not safe, as this implant can become infected and affect the others at some point. Now the question is whether the implant is loose or the top component of the implant is loose. If it is the top component, that potentially could be an easy fix, and the implant could be used to stabilized the restoration. Visit your surgeon for an evaluation.
Good Luck to you!!.
Dr. Juan C. arroyo
Oral & Maxillofacial Surgeon

If its verified that the actual implant is mobile and not just one of the multi-unit connectors, then ideally replacing the implant would be a good choice. However, if there is no infection and the oral surgeon feels that the implant can  be stabilized by performing, perhaps, a debridement followed by bone grafting, this may be something to consider. Of course the implant will be left dormant, or out of occlusion, during osseo integration to insure that the implant is not affected by your biting forces while it heals.You had mentioned that 1 of 5 implants are loose. If the implant has to be removed, its good to know that Fixed hybrid restorations (Used with the All on 4 treatment) can work with as little as 4 implants. So while a new implant heals you should still be able to wear your fixed hybrid denture. Given that this does not affect the load distribution on the denture or cause unnecessary force on the other implants. 

After an initial healing time, we go back to implants to impress/restore.  Sometimes when we test the implants, we find that they aren't stable enough.  YET.  Often, we can simply wait a few more months and the stability is fine and we can restore.  If not, we remove the implants and start over when bone has healed.  If no infection is present, implants can be left alone and ignored (called sleeping implants; this preserves bone height and width).