## 4 Discussion
The difference in the characteristics of change between standard gray resin and Mazic D resin seems to be due not only to the difference in initial polymerization due to the difference between SLA and DLP but also to the faster polymerization rate of MAZIC D resin during the postcuring period. Preventing such a dimensional change due to the presence of residual monomers requires the manufacturer's instructions to be followed exactly. However, since many CAD/CAM systems are open-source systems and due to various types of 3D printers, software, and materials being used by clinicians and laboratories, the manufacturer's instructions related to the use of standardized company equipment and resins might diverge. In addition, it should be considered that the postcuring time may vary with the values set for 3D printing devices [25]. When using MAZIC D resin and a DLP 3D printer, continuous errors were observed in the maxilla regardless of the postcuring time or presence of a support structure. The larger error for the maxilla than for the mandible was attributed to the large error in the palate area. The palate of the maxilla can play a role in maintaining the dimensional stability of the fabricated object, such as a support structure used in the 3D printing process does, but unlike the support structure, it is an area that is used without being removed. [PERSON] et al. [12] recently found both positive and negative errors in the maxillary palate for maxillary denture bases produced using the DLP 3D printer, which is similar results to this present experiments. Those authors attributed the geometry deviations to the 100-degree construction angle and sagging of the liquid material under its own weight. This analysis can be supported through the result that palate error is small even in the milled type manufacturing method [12; 30]. In addition, in the postcuring process, since there may be a difference in the shrinkage between the part that is directly irradiated with UV light and the part that is not directly irradiated with UV light, this may cause bending and lead to an error in the denture base [20]. In this study, the average RMSE values of standard gray resin and MAZIC D resin were similar, but in the color map shown in Figure 7, it was confirmed that the overall deviation of MAZIC D resin was large. This trend was especially observed in the maxilla, and it can be confirmed through the fact that the standard deviation value of MAZIC D resin is higher than that of standard gray resin in all postcuring time periods. Recent comparative studies found that the accuracy of 3D printing methods was equivalent to or better than those of existing milling methods [21; 26; 27], although inaccurate and irreproducible results have also been reported [24; 25]. It is noteworthy that these studies involved various postcuring times and support-structure removal times. Those experiments applied postcuring times such as 10, 15, and 30 min, or the exact time was not recorded [10; 24; 25; 27]. More accurate comparative experiments require the postcuring time to be properly controlled and recorded, given that this is a very important parameter. The present study was subject to some limitations. Since the required postcuring time varies with the 3D printer, material type, and light source (e.g., its wavelength and intensity) of the postcuring device, standard guidelines cannot be determined solely from the results of this study. In addition, while two types of materials, 3D printers and denture bases with a uniform thickness, were used in the present experiments, the diversity of materials and equipment will be greater in in vivo applications, and the thickness will vary according to the type of residual ridge. Future studies involving various types of equipment, materials, layer thicknesses, and irregular shapes may provide more meaningful guidelines for the optimal conditions to use when producing prostheses using 3D printing technology.