#### Article
###### Abstract  
The study aimed to evaluate the time-related accuracy of additively manufactured dental casts and to compare it with scan data obtained with an intraoral scanner in vitro. Twenty-eight markers were attached to a set of dendrimers as reference model, and the distances between the markers were measured using a digital caliper. An intraoral scanner was used to obtain the virtual scan data of the reference model with a total of 30 scans per arch. The distances between markers were measured using a three-dimensional inspection software for all scans (group IOS). Scan data were additively manufactured using a 3D printer, and the distances between markers were measured as in the reference model immediately after post-polymerization (group PPIA), 1 day (group PPID), 7 days (group PPTD), and 30 days after post-polymerization (group PP30D). The linear deviation in group IOS was 199.74 \(\pm\) 11.14 \(\upmu\)m, PPIA was 242.88 \(\pm\) 49 \(\upmu\)m, PP1D was 259.9 \(\pm\) 42.59 \(\upmu\)m, PP7D was 289.82 \(\pm\) 39.74 \(\upmu\)m, and PP30D was 315.8 \(\pm\) 33.28 \(\upmu\)m, in comparison with the reference model, with significant differences among all groups (all \(p<0.05\)). When additively manufacturing casts from scan data to verify the quality of dental prostheses designed virtually, the prostheses should be adapted to casts manufactured within one week.  
accuracy; additive manufacturing; cast-free digital workflow; direct digitization; postpolymerization  
28 March 2022221 April 20  
highly accurate. Employing additive manufacturing processes in the fabrication of dental casts requires less equipment and fewer materials while reproducing complex structures with high precision [14; 15; 16; 17; 18; 19].  
A previous study reported clinically acceptable accuracy and reproducibility of the additively manufactured dental casts compared to dental plaster casts fabricated using the traditional method [20]. Another study reported the higher accuracy of additively manufactured dental casts than that of milled casts [17]. However, additively manufactured dental casts may experience shrinkage, distortion, and deformation, because a photopolymerizing resin is used as a substrate [21; 22; 23; 24]. As various factors can affect the accuracy of additively manufactured dental casts, several studies have investigated them under diverse conditions, such as additive manufacturing methods, printing angulation, or printing time [25].  
In clinical situations, a cast-free digital workflow for the fabrication of implant prostheses is becoming popular. However, concerns regarding the absence of a dental cast exist due to the difficulty in directly viewing, sensing, and evaluating the harmony of the implant prostheses with the adjacent teeth and soft tissues. It is therefore beneficial to not only evaluate the prostheses virtually on CAD software, but also to place the prostheses on additively manufactured dental casts [26; 27]. However, studies comparing the accuracy of additively manufactured dental casts with that of virtual data from an intraoral scanner are lacking.  
The aim of this study was to investigate the dimensional stability of additively manufactured dental casts over time in reference to a physical reference model, and to compare the additively manufactured dental casts with the scanned data of this reference model obtained with an intraoral scanner. The null hypotheses were that additively manufactured dental casts neither differ in terms of dimension over time nor do they differ from intraoral scan data.