###### Abstract  
The objective of this study was to propose a standardised methodology for assessing the accuracy of three-dimensional printed (3 DP) full-arch dental models and the impact of storage using two printing technologies. A reference model (RM) comprising seven spheres was 3D-printed using digital light processing (MAX UV, MAX) and stereolithography (Form 2, F2) five times per printer. The diameter of the spheres (\(n=35\)) represented the dimensional trueness (DT), while twenty-one vectors (\(n=105\)) extending between the sphere centres represented the full-arch trueness (FT). Samples were measured at two (T\({}_{1}\)) and six (T\({}_{2}\)) weeks using a commercial profilometer to assess their dimensional stability. Significant (\(p<0.05\)) contraction in DT occurred at T\({}_{1}\) and T\({}_{2}\) with a medium deviation of 108 \(\upmu\)m and 99 \(\upmu\)m for MAX, and 117 \(\upmu\)m and 118 \(\upmu\)m for F2, respectively. No significant (\(p>0.05\)) deviations were detected for FT. The detected median deviations were evenly distributed across the arch for MAX at \(<\)50 \(\upmu\)m versus F2, where the greatest error of 278 \(\upmu\)m was in the posterior region. Storage did not significantly impact the model's DT in contrast to FT (\(p<0.05\)). The proposed methodology was able to assess the accuracy of 3 DP. Storage significantly impacted the full-arch accuracy of the models up to 6 weeks post-printing.  
three-dimensional printing; dimensional stability; dental models; methodology; accuracy; storage +
Footnote †: journal: Applied Sciences
The accuracy of 3D printed dental models has been extensively researched, with a recent systematic review identifying their accuracy varies significantly, between <100 and >500 um, not only between different printing technologies but also within studies evaluating similar 3D printers [1]. [PERSON] et al. [1] attributed this to the heterogeneity of the study designs in the included studies, which led to a high risk of bias, calling for standardised testing and reporting protocol in studies investigating 3 DP accuracy.  
Furthermore, there is currently limited evidence in the existing literature investigating the impact of storage on the dimensional stability of 3D printed dental models [1,11]. Additionally, and to the authors' knowledge, no studies have investigated the full-arch dimensional stability of 3D printed models. As stated by [PERSON] et al. [11], the fabrication of all types of dental prostheses and appliances is currently not plausible solely through the digital workflow, often requiring analogue input. Therefore, in cases where a combination of analogue and digital workflow is required, the dimensional stability of 3D printed models becomes of direct clinical interest. The dimensional stability of 3D printed models is of critical importance in cases of limited access to 3D printers where service delays are inevitable: increased workload, lack of in-house facilities, and shipping needs of rural and outreach locations. Further complicating the streamlining of the hybrid workflow is the potentially extended time needed for the actual printing of the dental model, inherently dependant on the printing system available, and could span to several hours per model. Henceforth, it is paramount that a 3D printed model remains dimensionally stable during storage to ensure the proper fabrication of the prosthesis for adequate seating, conformity with the patient's stomatognathic system and the planned treatment especially in multi-unit indirect restoration that requires a passive fit upon insertion, and surgical guides for accurate implant placement [11,12]. If, however, 3D printed models do demonstrate dimensional changes with storage, then such changes should be accounted for as part of the validation process of the workflow.  
The objective of this study was to propose a standardised methodology for assessing the accuracy of 3D printed full-arch dental models and the impact of storage on the dimensional stability using two commercially available 3D printing systems.