Reverse scan body: A complete digital workflow for prosthesis prototype fabrication

Abstract

Purpose To assess the accuracy of fit of prosthesis prototypes fabricated via a complete digital workflow protocol with a reverse scan body skipping intraoral scanning for implant data acquisition. Materials and methods A maxillary stone cast with four multiunit abutment implant analogs (Screw‐Retained Abutments, Institut Straumann AG, Basel, Switzerland) with adequate anteroposterior spread simulated a common clinical patient situation. This stone cast served as the master cast and an interim screw‐retained prosthesis was fabricated on it. Novel reverse scan bodies were connected to the interim prosthesis, and extraoral scanning was performed with a white light intraoral scanner. The produced standard tessellation language (STL) files were then imported to computer‐assisted design software and after the digital design, the STL file was exported to a computer‐assisted machining milling machine and a three‐dimensional (3D) printer to produce a total of 50 milled and 50 printed fixed complete denture prototypes, respectively. Two clinicians assessed the accuracy of fit of each digitally fabricated prosthesis prototype on the master cast, utilizing the screw‐resistance test and radiographic evaluation. Out of the 100 prototypes, 94% (94/100) were fitting accurately. Fisher's exact test was used to test the difference among the groups. The test revealed statistically significant results (p = 0.027). Results Out of the 50 digitally fabricated milled prosthesis prototypes, 50 (100%) presented with accurate fit under in vitro assessment. Out of the 50 digitally fabricated 3D printed prototypes, 44 (88%) presented with accurate fit under in vitro assessment. Conclusions Accurately fitting digitally fabricated prosthesis prototypes can be milled after extraoral scanning with reverse scan bodies without intraoral implant data acquisition.

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

“…[15][16][17] In the clinical scenario, it is imperative for the clinician to ensure the interim conversion prosthesis is passively fitting, has appropriate hygienic intaglio contour, is restored at the appropriate vertical dimension of occlusion, and meets the esthetic and phonetic parameters for the patient. 12,13 Additionally, it is incumbent that prior to the extraoral scanning of the immediately loaded interim (conversion) prosthesis, the clinician torque tests the MUAs to ensure they are not loose. 12,13 Once assured, the interim prosthesis can be used for this technique.…”

“…12,13 Additionally, it is incumbent that prior to the extraoral scanning of the immediately loaded interim (conversion) prosthesis, the clinician torque tests the MUAs to ensure they are not loose. 12,13 Once assured, the interim prosthesis can be used for this technique. If the interim prosthesis is not passively fitting, then the clinician needs to achieve passivity of fit by sectioning and re-luting the interim prosthesis prior to extraoral scanning.…”

“…Similarly, in the present in vitro study, the interim prosthesis was fabricated on the reference cast, and passive fitting was confirmed prior to the digital scanning procedures. The reverse scan body protocol basically simulates the back‐pouring technique in a digital workflow and produces accurately fitting digitally fabricated prototype prostheses by skipping implant data acquisition with intraoral scanning 12,13 …”

“…There are many advantages to the reverse scan body concept 12,13 . The number of clinical appointments can be reduced from the five‐appointment analog workflow to three appointments, or even two if a prototype is not necessary.…”

“…[3][4][5] The reverse scan body concept was recently introduced, and promising results were shown with extraoral scanning to overcome intraoral limitations. 12,13 The main parameters affecting the accuracy of intraoral complete-arch digital scans are the inter-implant distance, scan body design, degree of alveolar ridge resorption and lack of keratinized mucosa, operator experience, and scanning pattern. 3,[14][15][16][17][18] The reverse scan body extraoral concept can be used in the workflow of the definitive prosthesis fabrication in three appointments including the digital data acquisition appointment (reverse scanning protocol), prototype prosthesis fabrication appointment, and the delivery appointment.…”