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  • Title: Reverse scan body: The scan pattern affects the fit of complete-arch prototype prostheses.
    Author: Papaspyridakos P, Bedrossian EA, Ntovas P, Kudara Y, Bokhary A, Chochlidakis K.
    Journal: J Prosthodont; 2023 Dec; 32(S2):186-191. PubMed ID: 37721306.
    Abstract:
    PURPOSE: To assess the effect of different scan patterns on the fit of implant-supported complete-arch prototype prostheses fabricated via a complete digital extraoral protocol with a reverse scan body. MATERIALS AND METHODS: A mandibular cast with four multi-unit abutment (MUA) implant analogs with adequate antero-posterior spread served as the reference cast, simulating a common clinical patient situation, and a polymethylmethacrylate interim screw-retained prosthesis was fabricated on it. Novel reverse scan bodies were connected to the interim prosthesis on the intaglio of the MUA abutments and extraoral scanning was performed with a white light intraoral scanner (TRIOS 4; 3 shape) and three different scan patterns: starting from the occlusal surface of the interim prosthesis (O-group), starting from the intaglio (I-group), and helix pattern (H-group).  The resulting STL files from the three groups were then imported to computer-aided design (CAD) software and after the digital design, the STL files were exported to a computer-aided manufacturing (CAM) milling machine which generated a total of 15 CAD-CAM milled prototype prostheses per group. Two clinicians assessed the fit of each digitally fabricated prototype prosthesis on the reference cast, utilizing the screw-resistance test and radiographic evaluation. Fisher's exact test was used to test the difference between the three groups, and Cohen's k-score was used to assess the inter-examiner agreement. RESULTS: Out of the three different groups, the O-group scan pattern led to 100% prosthesis fit, while the prototype prostheses generated from I- and H-groups had 80% and 53% fit, respectively. The results were statistically significant (p = 0.008). CONCLUSIONS: Occlusal scan pattern leads to fitting milled prototype prostheses after extraoral scanning with reverse scan bodies without intraoral implant data acquisition.
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