# Accuracy Comparison among 3D-Printing Technologies to Produce Dental Models
## 2 Materials and Methods  
For the purpose of this in vitro study, a cone beam computer tomography (CBCT) was performed on a resin dental model with tomographic hyperdensity (tomographicable model; BoneModels; Castellon; Spain), shaped according to a human maxilla. Digital Imaging and Communications in Medicine (DICOM) files obtained were then converted into an STL file using a CBCT software (Nemo Studio; Nemotec SL, Madrid, Spain). The resulting STL file was imported and virtually measured using a 3D analysis software (DentalCAD 2.4 Matera, Exocad GmbH, Darmstadt, Germany). Digital small marks with 1 mm in diameter were added to specific places on the buccal and palatal plates of the maxillary ridge (simulating buccal-lingual width measurements of edentulous area commonly performed during dental implant planning) to ensure reproducibility of the linear measurements of the buccal-lingual width of the alveolar ridge, performed for trueness analysis, following a previously described methodology [1]. Figure 1 shows in a smaller STL file of a dental crown how the digital markers were created using the CAD software of this study and how the digital linear measurements were performed. Briefly, the middle point of the upper limit of the mesh area of each digital mark was considered the point at which to start and finish each linear measurement, as this point was also planned to support the tip of the digital caliper on all 3D-printed dental casts. Furthermore, cross-section views of the mesh area containing the measurement were also created by the CAD software and used to orientate all digital linear measurements. Digital linear measurements were used as control values to be compared with the measurements performed directly on the 3D-printed dental casts. Figure 1: Example of the linear measurement procedure used in this study (dental CAD software, Exocad GmbH). In this example, an STL file of a tooth has 1 mm markers on the 4 axial surfaces (buccal, palatal, mesial, and distal). The figure shows a linear measurement performed between mesial and distal digital markers. Note that since both markers are in different heights, the cross-section view (bottom right) of the CAD software was used to orientate the measurement to be performed between the exact sites that the tips of the digital caliper could touch to make the physical measurements, as performed in the present study. This file was imported into the corresponding slicing software programs of each of the following 3D printers: Obiet30 Dental Prime (Stratasys, Minneapolis, MN, USA); Form 2 (Formlabs, Somerville, MA, USA); Sonic Mini (Phrozen, Hsinchu, Taiwan); Photon (Anycubic, Shenzhen, China); and Miicraft 125 (Miicraft, Jena, Germany). All 3D printers were previously calibrated and all 3D-printing parameters adjusted according to the 3D printer and resin manufacturer's instructions (Table 1). Before starting the study, representative test specimens with known dimensions provided by the manufacturers were printed with all 3D printers and measured to confirm successful calibration. A total of 15 dental casts were manufactured with each 3D printer. Dental models manufactured with Stratasys were 3D-printed using a light-curing resin of the same brand (VeroDent Plus MED690), whereas all other models were fabricated with an independent light-curing resin brand (Prizma 3D Model, Makertech Labs, Tatui, Brazil). This resin brand produces different resin bottles specifically designed for either SLA, LCD, or DLP technology. Therefore, the appropriate bottle of Prizma 3D Model resin was chosen for each 3D printer technology. The light-cured resins of this work were composed mainly of monomers and oligomers and was specifically developed to produce dental casts. After 3D-printing, all models were washed and postcured for 10 minutes in a standard UV light-curing chamber. The following measurements were performed with the aid of the locating marks: left posterior buccal-lingual width; right posterior buccal-lingual width; and anterior buccal-lingual width.