Tolerance analysis for cast vs machined dental implants

The paper addresses the dimensional tolerance and assembly accuracy of prosthetic components obtained by different manufacturing processes. The success of single tooth implant replacements hangs on the stability of the hexagonal connection, but no standard control procedures are available for its evaluation. The research aims at proposing a new protocol for the dimensional assessment of implant-abutment connections, based on non-contact measurement and statistical data processing. The procedure is applied to machined- and cast-on abutments, as well of the matching implants. Samples are measured using an optical measuring microscope and data are processed to obtain the international tolerance (IT) grade. The rotational misfit is then calculated using the apothems of the external and the internal hexagon. As to the results, all the components are classified between IT8 and IT9 and the maximum rotational misfit is around 4° for all the assemblies, inferior to the critical limits for the screw joint stability. An objective dimensional characterization of prosthetic components and assemblies is reported, which is the basis for their reliability in clinical applications. From a wider perspective, an original measuring protocol is proposed, independent of parts assembly and based on international tolerances.