All on 4 dental implants are loose - what can be causing this?

All on four can come loose due to bite issues.

If the dentist is not using a torque wrench to tighten screws correctly it can also be an issue.

Hello. Prosthesis should fit onto the implants passively. This type of loosenings may be associated wit a non-passive fitting prosthesis which may require to renew the prosthesis. Another factor may be worn prosthetic screws. Sometimes the screws that comnect implants to prosthesis may wear in laboratory processes and of a screw loosens, it generally should be renewed rather than re-tightening.
This type of problems may cause damage to the implants. So, it has to be taken care of.Kind regards.Dr Kerem Turgut Atasoy

If you had had a tooth which was extracted before, or any infection or unsterilized part, the implant may fall. Things such as smoking, insufficent bone density, a surgery in unsterilized area, loading the teeth right after the implant surgery and no osseointegration period, and medical conditions can cause this problem.

It is important to know WHAT is loose, since tightening something that ISN'T loose just leads to frustration. There are three parts to dental implant restorations: the fixture (looks like a screw, goes into the bone), the restoration (the crown or bridge), and the abutment (the connector between the restoration and the fixture). The fixture gets inserted into the bone, the abutment gets screwed into the fixture, and the restoration gets secured to the abutment. It is possible that the screws connecting the bridge are tight but the abutment is not, and the micro movement makes everything else get loose.

Or the implants broke.