## 4 Discussion  
In the field of fixed prosthodontics, the rehabilitation of cases with complex cross-arch-fixed dental prostheses is a difficult procedure. Generating an accurate final impression including the prepared teeth and the entire arch is critical to ensure precise fitting and long-lasting definitive restorations [4]. According to the ADA specification on impression materials, there are specifications to test their accuracy and ability to reproduce fine details using simulated tooth models presenting areas that can be easily measured [14]. The testing conditions embodied in the specifications differ from those encountered during clinical practice; therefore, in the present study, a typodont master model with full-arch-prepared abutment teeth was used. A TRIOS-3 3 Shape intra-oral scanner was used in the current study, as a previous study reported the highest precision for this scanner compared to other intra-oral scanners used in dentistry [13]. As reported in a previous study [12], instead of using digital versions, casts were printed to standardize the groups in order to have the same testing conditions and to avoid any errors, while measurements were made using a stereomicroscope. The distance between the casts and microscope was standardized and a ruler was used for calibration during measurement using the software. The readings obtained after evaluating the discrepancies of the casts contained both negative and positive values. These were converted to absolute values to avoid false results that could occur due to the positive and negative values canceling each other out [15,16]. Furthermore, in the present study, the die stone casts obtained from PVS-2 presented the highest accuracy compared to the casts obtained from the alginate impression material and digital impressions. This result was supported by other studies that found that the accuracy of full-arch conventional impressions was better than the digital impressions [4,5,7]. The high accuracy of the additional silicon two-step putty-light body technique can be explained by the uniform space for the light body material to polymerize with minimal shrinkage, and the details were recorded by the light-body material only [17, 18, 19]. The 3D-printed models obtained from the intraoral scanning digital impression did not exhibit superior accuracy compared to the stone casts obtained from the conventional impression materials (ALG and PVS-2). This result is supported by several in vitro studies [4,5,7,12]. An in vitro study found that the local deviations of full-arch impressions were higher for digital impression systems than for conventional impression methods [4]. Additionally, it should be noted that most previous studies involved dentulous patients or those with a single missing tooth. However, there is a paucity of literature evaluating the precision of intraoral scanners in partially edentulous cases. Figure 6: Percentage of deviation from the typodont master cast for the impression materials and CAD/CAM. The present study included a full dental arch with multiple edentulous areas and prepared abutment teeth to imitate the clinical scenario of a complex case. Comparing the result of the present study (full arch) with that of our part 1 study (half-arch), the accuracy of the stone casts produced by both 3M ESPE PVS and the Kromopan alginate impression materials and the digitally printed models was better in the half arch than the full arch [12]. The precision of digital impressions was anticipated to be less in cases where multiple teeth are missing due to a deficiency of reference points from the scanning machine and the dentist [20]. In the current study, the only measurement that did not exceed 0.5% in dimensional change was with the stone casts produced by both 3M ESPE PVS and Kromopan alginate impression materials at the HAPC dimension.