Comparison of Milled Full-Arch Implant-Supported Frameworks Realised with a Full Digital Workflow or from Conventional Impression: A Clinical Study

Abstract

Background: The aim of the present study was to investigate the accuracy of a new digital impression system, comparing it to the plaster impression technique in the realization of full-arch implant-supported metal frameworks. Methods: We took 11 scans (8 of the upper maxilla and 3 of the lower jaw) on a sample of nine patients previously rehabilitated with fixed full-arch screw-retained prostheses following the Columbus Bridge Protocol (CBP) with four to six implants (total: 51) since at least 4 months. Two impressions were taken for each dental arch: one analogic plaster impression using pick-up copings and an open tray technique and a second one using an intra-oral scanner. Two milled metal substructures were realised. The precision and passivity of the substructures were clinically analysed through the Sheffield test and endo-oral radiographs. Laboratory scans of the plaster casts obtained from an intra-oral scanner (IOS) and of the plaster casts obtained from traditional impression were compared with the intraoral scans following Hausdorff’s method and an industrial digital method of optical detection to measure discrepancies. A Mann–Whitney test was performed in order to investigate average distances between surfaces after the superposition. Results: The Sheffield test demonstrated an excellent passivity of the frameworks obtained through both the digital and the analogic method. In 81.81% of cases (n = 9) both substructures were found to have a perfect fit with excellent passivity, while in 18.18% (n = 2) of cases the substructures were found to have a very slight discrepancy. From the radiographic examination, no gaps between the frameworks and the implant heads or multiunit abutments were observed, with 100% accuracy. By superimposing digital files of scans according to Hausdorff’s method, a statistically significant discrepancy (p = 0.006) was found between the digital scans and the digital models obtained from plaster impressions. Three-dimensional optical detection found a mean discrepancy of 0.11 mm between the analogic cast and the cast derived from the digital impression. Conclusions: The present study clinically demonstrates that milled implant-supported full-arch frameworks obtained through a digital scan and the herein described technique have an accuracy comparable to those obtained with traditional plaster impression.

Conventional and Digital Impressions for Fabrication of Complete Implant-Supported Bars: A Comparative In Vitro Study

“…Additionally, superimposition of images often occurs in the absence of fixed anatomic references and the presence of similarities in the morphology of scanbodies [29,34]. Mandible/tongue movements, excessive salivation, and operator experience are other complicating factors [33,38]. In the present in vitro study, the scanning process was performed in a parallel-implants stable model without movements, tongue superimposing, moisture, or saliva, leading to caution in interpreting results.…”

“…It seems that the open tray with splinted transfers associated with high-precision elastomers such as VPS or polyether is the most accurate technique to obtain working models for implant-supported prostheses [10], and the present study used this method for the conventional impression group. Studies and reviews have attempted to elucidate the feasibility of using intraoral digital impressions in full-arch implant-supported prostheses cases, with general agreement on the challenges associated with the technique [12][13][14]17,[24][25][26][27][28][29][30][31][32][36][37][38]. The large area to be scanned increases the risk of minor deviations accumulating during the formation of three-dimensional (3D) images [29].…”

“…However, in multiple implants [24], especially for full-arch cases [17,[25][26][27][28][29][30][31][32][33][34][35][36][37][38], intraoral digital impressions still lack predictability. Numerous methods have been used to assess the quality or accuracy of intraoral digital impressions for multiple implants.…”

“…They can measure the 3D deviation and, consequently, the trueness and precision between the experimental models and the master model without the need to construct prostheses. Other studies analyzed the quality of fit directly in the prostheses utilizing radiographic analysis [36,38], strain recording [15], optical microscopy [34], and the Sheffield test [36,38]. Based on the findings of some of these studies evaluating digital impression, it has been suggested that it may not be suitable for routine clinical use in full-arch prostheses [16].…”

“…More recently, a clinical study which compared full-arch implant-supported prostheses made using conventional and digital intraoral impressions found no differences in the fit quality between both methods. Nevertheless, digital analysis resulted in prostheses with better accuracies [38]. Thus, despite the evident progress observed in recent studies, there is still no consensus on whether intraoral digital impressions can be regularly used to produce complete implant-supported dentures.…”