Abstract
For digital impression-making of two-piece oral implants, scan bodies are used to transfer the exact intraoral implant position to the dental laboratory. In this in vitro investigation, the accuracy of digitizing a one-piece ceramic oral implant without a scan body (OC) was compared to that of a standard two-piece titanium implant with a scan body (TT) and a preparation of a natural single tooth (ST). Furthermore, incomplete scans of OC simulating clinical compromising situations (OC1–4) were redesigned using a virtual reconstruction tool (RT) and superimposed to OC. OC and TT oral implants and one ST were inserted into a mandible typodont model and digitized (N = 13) using two different intraoral scanners. The resulting virtual datasets were superimposed onto a three-dimensional (3D) laser scanner-based reference. Test and reference groups were aligned using an inspection software according to a best-fit algorithm, and circumferential as well as marginal discrepancies were measured. For the statistical evaluation, multivariate analyses of variance with post-hoc Tukey tests and students t-tests to compare both scanners were performed. A total of 182 datasets were analyzed. For circumferential deviations, no significant differences were found between ST, TT, and OC (p > 0.964), but increased deviations for OC1–4 (p < 0.001) were observed. The measurements of the marginal deviations revealed that ST had the smallest deviations, and that there were no significant differences between TT, OC, and OC1–4 (p > 0.979). Except for marginal deviation of OC (p < 0.001), the outcome was not affected by the scanner. Within the limitations of this study, digitization of OC is as accurate as that of TT, but less than that of ST. In the case of known geometries, post-processing of compromised scans with a virtual reconstruction results in accurate data.
Highlights
For the manufacturing of a tooth- or implant-borne prosthesis, the shape and position of teeth and oral implants need to be transferred to the dental laboratory in a highly accurate and reliable procedure
The implant-abutment connection (IAC) of an oral implant has a standardized geometry, and in-lab implant replicas with identical IACs are used for subsequent manufacturing of the restorations [6]
As passive fit of implant-borne superstructures seems mandatory for long-term clinical success [11,12,13], it is recommended to splint impression copings in the case of multiple adjacent implants to minimize the risk of discrepancies caused by deformation of the impression material [11]
Summary
For the manufacturing of a tooth- or implant-borne prosthesis, the shape and position of teeth and oral implants need to be transferred to the dental laboratory in a highly accurate and reliable procedure. For the “transfer method” impression technique a transfer cap attached to the impression coping remains in the impression material after setting and removal from the oral cavity of the closed tray [7]. This allows repositioning of the impression coping with an attached lab-replica of the implant prior to pouring. The majority of in vitro investigations have confirmed the benefit of splinted copings in edentulous and partially edentulous patients in the case of ≥4 implants [12]
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