When prosthetic materials are not durable, like with acrylic based hybrid fixed prosthetics, retrievability may have a relatively high value, so that it will be possible to make necessary repairs or refurbish the prosthesis. When prosthetics are durable, like solid zirconia bridges, do you ever expect to take them out for repair? If they have porcelain on them and the porcelain has a critical fracture, can the dental laboratory equipment really fix the prosthesis or will it be a remake anyway?

I would suggest that it will usually be the later. What about loose screws? What do you think will have more loose screws? A prosthesis with a misfit at the implant-abutment junction, like a screwed-in multi-unit hybrid, or one with an optimized implant-abutment fit? So, optimizing the fit of the implant-abutment junction and proper torqueing and re-torqueing of the abutment and would be expected to further reduce abutment screw loosening to an unusual event.

Do you need to be able to remove a prosthesis from the mouth in order to tighten a loose abutment screw? That is usually not necessary. In most locations, an access hole can be made through the prosthesis and the loose abutment screw can be tightened without removing the prosthesis. In the anterior maxilla, there might be an advantage to have a lingual access channel for possible screw tightening procedures, because making a facial screw access channel opening could render the prosthesis unaesthetic. This could be a cause for prosthesis replacement.

It is also unfortunate that the lingual access channel may require the clinician to build a facial cantilever into the prosthesis. This may also cause additional mechanical stresses on the abutment screw and make the prosthesis difficult to maintain by the patient. Both of these problems may feed into the peri-implant disease process and cause the failure of the retaining implant(s) and their attached prosthesis. So, building retrievability into a treatment is dependent on many elements that are not free of cost and risk.

Dental milling technologies, that are CAD/CAM based, have allowed the dental industry to create increasingly precise implant-abutment components. Milled components can be made to fit better and thus be more stable and resist bacterial penetration better. Beware of older technologies that require a casting process that can distort the milled implant-abutment connection. The UCLA bases are precision milled, but the casting process can damage their fit by temperature related distortion and mechanical removal of investment material. 29 A poor implant-abutment fit can lead to increased complications.

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