Optical Scan Analysis to Detect Minor Misfit on Implant-Supported Superstructures

Purpose: Despite the development of novel and more precise fabrication methods, absolute passive fit of implant-supported superstructures has yet to be consistently achieved. In the past, several laboratory techniques have been described to analyze fit. The purpose of this study was to assess two methods of fit evaluation with a control (well fitting) prosthesis and an intentionally misfit prosthesis. Materials and Methods: In this in vitro study, two comparable implant-supported superstructures (control and test misfit) were fabricated after scanning a test cast of a maxilla with four implants (two on each side). The test structure was fabricated with a known minor misfit on one of the inserted implants by manipulating the coordinates on the scanned files. The control superstructure was fabricated as accurately as possible without manipulating any scanned information. Both superstructures were evaluated using optical scanning and strain gauge measurements by an investigator who was blinded to the designed misfit. Results: Optical scanning demonstrated an accuracy of 10 µm for the control frame, while the misfit frame demonstrated greater discrepancies, both at the intentionally misfit connection (connection #2, misfit of 29 µm) and at the other connections (#1, 4 µm; #3, 5 µm; #4, 4 µm), although the latter connections showed less misfit. The strain gauge measurement showed a higher mean deviation of 26.2 µm (± 5.9 µm) in the test model, versus 15.3 µm (± 4.3 µm) in the control model. Conclusion: Optical scan analysis was able to detect the misfit in the test superstructure and the manipulated implant. The strain gauge measurements confirmed these findings, indicating that both methods of assessing inaccuracy are effective. Optical scan analysis may be used as a simplified and clinically applicable method to detect minor misfits in implant-supported superstructures. Keywords: implant superstructure, optical scan analysis, passive fit, prosthesis, prosthetic misfit, strain gauge