Reverse scan body: The scan pattern affects the fit of complete‐arch prototype prostheses

Abstract

AbstractPurposeTo 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 MethodsA 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.ResultsOut 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).ConclusionsOcclusal scan pattern leads to fitting milled prototype prostheses after extraoral scanning with reverse scan bodies without intraoral implant data acquisition.