Want to know more about the Sheffield screw test for dental implant prosthesis?
Sheffield screw test is a one screw test that dentists use to check the passivity fit of a dental prosthesis. Typically this is an all on 4 or all on x prosthesis. It is a very common technique in implant dentistry.
When do you need to do a 1 screw test?
The Sheffield screw test is useful whenever you are delivering a multiple implant prosthesis. Whether it is the final delivery or a step to fabricate the prosthesis, any time a new step is taken it’s important to check fit. It helps to ensure the fit of the prosthesis is passive. A non-passive prosthesis will have more load on the screws and the prosthesis itself and can cause fractures or breaks of either the screw or the prosthesis. We do the Scheffield screw test when making any all on x prosthesis, multiple times. First we do the test with the verification jig. If this is accurate then most likely so will everything else. We also do this with the PMMA temp and the final prosthesis.
What are the steps for the one screw test?
There are some mild variations in the test but for the most part everyone does it the same. The short version is you tighten only one screw and check the fit of the prosthesis to the other implants. This can be done visually and with radiographs. We just check visually with 8x magnifcation dental loupes. Radiographs can be deceiving due to angle or technique of the radiograph according to Daros JPD 2018. You will also check for any rock of the prosthesis. Then you remove that screw and do the next one. We continue this process until every implant proves that the screw tightening still allows passive fit of the rest of the prosthesis.
Problems that can screw up, get it?, the Sheffield test.
Want to verify nothing is holding up the prosthesis and making the screw artificially tight because of contact somewhere. The biggest issues when doing this are tight interproximal contacts when dealing with a prosthesis that is not the full arch. The other major issue that can happen with any prosthesis is the squeezing of the gingiva. This can be hard to see if it occurs under a pontic. To check this sometimes you need to use some type of fit check PVS. When it happens on the buccal or lingual it is easier to see with tissue blanching.