Optical measurement methods of the 3D-position stability of implant-abutment connections - an in vitro study.

Abstract

Introduction: For ideal occlusion and passive fit of implant-retained prosthetic restorations minimal tolerance of the position of the abutment in the implant after dis- and reassembly is essential. Methods to examine the three-dimensional (3D) positional stability of implant-abutment connections (IAC) vary and their accuracy and applicability have not been assessed. The aim of this study was to evaluate non-contact optical measurement devices for 3D-feasibility, accuracy, repeatability, time efficiency and complexity of use.

Methods: Five devices capable of contactless, optical methods (Profile Projector; Digital Image Correlation (DIC); Profilometer; Confocal Technology; Coordinate Measuring Machine (CMM)) were examined regarding their 3D-feasibility, accuracy, repeatability, time efficiency and complexity. The parameters were quantified and scored using a decision matrix. In an experimental set-up the method (device) with the highest score was used to measure the position stability as follows: four implants with a butt joint (BJ) and a conical (CON) IAC were embedded in an aluminum block and dis- and reassembled ten times with the abutment screw being hand-tightened (∑1-5) and torque-tightened (∑6-10).

Results: The CMM achieved the highest score in the decision matrix with 40/50 points (range: 10-50 points; 10 requirements not met, 50: requirements fully met) while the Profile Projector, the DIC, the Profilometer and the Confocal Technology achieved 30, 32, 34, 38 points, respectively. Using the CMM the mean rotational freedom in BJ vs. CON was 0.32° ± 0.16° vs. 0.21° ± 0.25° (hand-tightened) and 0.36° ± 0.09° vs. 0.20° ± 0.22° (ratchet), respectively. The maximum vertical deviation of the abutment position after re-assembly was 7.2 μm ± 2.1 μm (BJ) and 24.4 μm ± 2.1 μm (CON).

Conclusion: The data acquired suggest that the CMM with its non-contact, optical measurement method is the most appropriate to investigate the 3D positional stability of the IAC in different implant systems. As previously described distinct differences between BJ and CON IACs were found. CON connections exhibit a higher vertical deviation when the system specific torque value was applied.