# Accuracy Comparison among 3D-Printing Technologies to Produce Dental Models
## 4 Discussion  
This study aimed to compare the accuracy of three different 3D-printing technologies used to manufacture dental models, SLA, DLP, and LCD 3D printers, in creating a final manufactured product (dental models). For this purpose, trueness and precision analyses were performed with a model resin commercially available generally available in the market. Our main outcome was a discrepancy between the referential measures on the original digital files that were manufactured and the physical measures on the manufactured models [11]. This is the first in vitro study to address the aforementioned differences between the 3D printers. Nevertheless, the present findings are consistent with previous studies that also compared 3D-printing technologies [4,5]. However, the clinical relevance of the accuracy differences found herein may not be clear, since several other studies confirmed that the 3D-printing methodologies lead to clinically acceptable outcomes, which were better than those observed in conventional cast models [11,12]. There were no significant differences in trueness and precision among all 3D printers (Friedmann test, \(p>0.05\)). Discussing this finding in relation with previous similar studies [13,14] is a challenge, as these studies were not able to standardize the materials used and the method of calibration of the 3D printers. Nevertheless, the absence of significant differences among 3D printers suggests that low-cost devices might perform at similar levels of trueness of highly priced devices, provided that the correct materials and methods are applied. On the other hand, pairwise comparisons showed that the PolyJet technology was significantly better in trueness and had greater reproducibility and reliability of measurements, especially compared to the 3D printer that showed the greatest deviation in median values from the control ones, which was the Anycubic Photon. This finding is in agreement with a previous study on dental models, which found greater accuracy for dental models 3D-printed using the PolyJet technology [13]. Figure 3: Median linear variations (in millimeters) and standard error of control (digital measurements performed on the CAD software), and digital caliper measurements on 3D-printed dental casts. Note that the Stratasys 3D printer (Polyjet) presented the closest values to the control digital ones. Measurements are shown in millimeters. Error bars are limited to the amplitude of the scale used to depict the differences found and showed similar results for all 3D printers. While this study solely assessed 3D-printing accuracy, other factors such as the cost relationship among 3D printers are important in 3D-printing comparisons for dentistry. For instance, the DLP technology enables fast light-curing 3D-printing and ensures high precision [15]. One of its biggest drawbacks of this technology is that it is relatively expensive and limited in size of the printing bed. The LCD technique, in turn, is also based on light-curing, but it uses liquid crystals instead of a light projector [16]. Compared to other 3D-printing technologies, LCD is more inexpensive and has good resolution, but it is known to have a shorter lifespan [17]. Factors such as time taken to 3D-print dental devices, cost, and production rates are important for comparison in research to assess whether the clinician can implement 3D-printing in its practice [18; 19]. The more automated the 3D-printing procedure is, the more acceptability from clinicians the procedure can achieve. In this context, some models of DLP 3D-printers that have user-friendly interfaces but that were not tested herein have also been used in studies validating dental techniques, such as The Hunter Printer (Flashforge, China) [19; 20]. Research and website validating 3D-printing software parameters for each light-cured resin can also be a useful tool to help the clinician and dental professionals to standardize the procedure used to manufacture dental devices in their practice.