## 2 Materials and Methods
### Stages of Additive Manufacturing  
1. Data collection was performed using the scan of the reference model as a benchmark for three-dimensional printing and comparison later in the study.
2. The analysis involved the virtual assessment of the object using a GOM Inspect 2020(tm) (Braunschweig, Germany) software package. After the design was loaded, the STL file was imported into the printer's software, followed by specifying the parameters for cutting and adding the support structures.
3. Printers were generally named Printer A and Printer B due to commercial reasons. Using photo-cured liquid resins (DentaMODEL(tm), Asiga, Sydney, Australia and NextDent(tm) Resin Model 2.0, Soesterberg, The Netherlands) eight three-dimensional models (Figure 2) were obtained as follows: - Printer A, using SLA printing technology, was used to obtain 4 three-dimensional models named Model A1, A2, A3, A4 (Figure 3A). Build volume of the pieces was 124.8 \(\times\) 70.2 \(\times\) 196 mm (4.9 \(\times\) 2.8 \(\times\) 7.7 in), with resolution 1920 \(\times\) 1080 pixels, pixel pitch 65 microns (0.0025 in) (390.8 effective PPI), wavelength 405 nm. - Printer B, using DLP printing technology, was used to obtain 4 three-dimensional models named B1, B2, B3, B4 (Figure 3B). The maximum construction volume of the workpiece was 119 mm \(\times\) 67 mm \(\times\) 75 mm, resolution 1920 \(\times\) 1080 pixels The printer used 385 nanometers in wavelength UV LED.  
At a later stage in the study, using the GOM ATOS Capsule (Zeiss(tm) Gmbh, Braunschweig, Germany) scanner, the models printed previously were scanned again for comparison with the benchmark. The models were covered with an antireflexive powder to avoid any shine and so that the measurement conditions were preserved for all  
Figure 1: Three-dimensional mesh of the reference model.  
Figure 2: Typodont and 3-D printed models used in the study.  
measurements. The results of the scanning were then exported in a STL format. A global standard best fit method was used to pre-align the reference and printed model. This minimizes the average deviations between the surfaces. A local best fit method was used to align the two surfaces in the teeth area as the global best first method aims at minimizing global deviations.  
The GOM Inspect 2020(tm) (Braunschweig, Germany) software package was used to measure and evaluate the accuracy of the models. The measurements were performed in the following incidences (schematically presented in Figure 4):  
* Interdental distances of the arches, inside and outside (Figure 4A,B);
* Deviations of the medium plane buccal-lingual (Figure 4C);
* Mesial-distal dimensions (Figure 4D);
* Height of teeth (Figure 4E);
* Curvature of the arch's length (Figure 4F).  
The width of the dental arch was obtained by measuring the inter-canine, inter-premolar and inter-molar distances on both tooth surfaces (internal and external) of each tooth. Tooth height was obtained by first calculating the distance between the gingival margin and the occlusal surface or gingival margin of each tooth. Arch curvature was  
Figure 4: Schematic representation of measurement directions (features).  
Figure 3: (**A**) Model manufactured through SLA; (**B**) Model manufactured through DLP.  
determined by the mid-buccal-lingual distance of each tooth. All measurements except for the tooth height were made in a horizontal section in the median level of the tooth height.  
The accuracy was evaluated by analyzing precision and bias for each feature (measurement direction). Precision is defined as a measure of how close together the measurements are, or how similar they are while bias measures how far the measurements are from the true value or reference ([[https://ag.arizona.edu/classes/rnn613/accuracy.html](https://ag.arizona.edu/classes/rnn613/accuracy.html)]([https://ag.arizona.edu/classes/rnn613/accuracy.html](https://ag.arizona.edu/classes/rnn613/accuracy.html)) (accessed on 11 January 2023)).