I feel that foreign matter plays a role in contamination of not only the implant fixture threads, but also the implant screw threads. This foreign matter is comprised of blood (body), calculus (body), wax (lab), porcelain powder (lab), metal filings(lab), and stone slurry (lab).  I also feel that the screw head may not seat properly in the screw access hole of the screw abutment, crown, and/or bridge prosthesis due to the same contaminants.

Screw loosening/fracture occurs:
1. When dentists and labs don’t recognize this debris as a contaminant.
2. The dentists and labs don’t use a new/unused screw for the final screw.
3. The proximal contacts of the crown and bridgework are too tight, putting excessive lateral pressure on the screw threads.
4. Calculus formation in the threads of loose screws will inhibit the dentist’s ability to remove the screw without fracture.
5. Screw metal surface quality may play an important role. You need to check with the implant manufacturers.

Presoaking the screw access hole with tarter/stain removing solution is my best advice for existing cases. Lab quality control starts with using advanced magnification such as a quality dental microscope.  GC