The metal structures made using the CAD/CAM technique fit better than the cast structures but do not pass the Sheffield Test as the passive fit cannot be obtained.
Only with the further optimized SAE spark erosion machine EDM 2000 (year of manufacture 2012) can the finest fit be achieved with the additional module "polishing erosion" (width of gap maximum 5 µm).
How does the Sheffield Test work?
A meaningful method for checking the passive fit is the Sheffield Test (White 1993). The Sheffield Test clearly shows the fit or misfit of the mesostructure on the model and in the mouth. With one screw, the mesostructure is firmly screwed onto the model on the distally positioned implant replica or abutment for checking (Eisenmann 2004). There mustn't be any gap between the mesostructure and the remaining abutments or implants. If a gap forms, there will not be an exact fit. Checking the fit is carried out in both directions on the mesostructure. This test is repeated on the bar and bridge try-in in the patient's mouth. An x-ray of the screwed-down mesostructure is not sufficient for establishing a passive fit.
The high level of precision demanded when creating the meso and suprastructure on implants is, however, only possible with consistent interdisciplinary cooperation between the dentist and dental technician based on tried and tested working steps and approved technical procedures.