## 4 Discussion  
The purpose of this study was to determine the dimensional stability of maxillary and mandibular edentulous denture bases according to the postcuring time and whether the support structure is present or removed during the postcuring process after 3D printing. Denture-based samples were constructed using 3D printers with two resins, and postcuring times of 0, 15, 30, 45, and 60 min were investigated. Three-way ANOVAs showed that when using the SLA-type Form3 printer and standard gray resin or the DLP-type Phrozen Shuffle printer and MAZIC D resin, the accuracy was significantly higher when postcuring was performed with the support structure present and higher for the maxilla than the mandible. The dimensional changes gradually accumulated, and the deviations increased with the postcuring time. Therefore, the null hypothesis of this study, that there are no dimensional changes according to the removal of the support structure, arch position, and postcuring time, was rejected. Most previous studies have found that digital dentures and record bases produced by 3D printing are highly accurate. In the present experiments, when using standard gray resin with the SLA-type Form3 printer, the error in the no-support group increased significantly with the postcuring time for both maxillary and mandibular denture bases. In the support group, there were significant changes as the postcuring time increased in the maxilla, but there were few changes in the dimension for the mandible and no significant differences according to the postcuring time (Figure 5, Table 2). [PERSON] et al. [24], which was designed to remove the support structure before postcuring, is noteworthy that the accuracy was inferior in their 3D printing group, which contrasts with other studies. Those authors observed a significantly larger dimensional difference for the maxillary edentulous denture base constructed using an SLA 3D printer than for the milled type of base. They attributed this observation to the deformation of partially polymerized prostheses during demounting or to polymerization shrinkage. Their analysis results are consistent with those of the present experiments, which showed that differences in dimensional changes appeared with or without a support structure. In both the SLA and DLP methods, the postcuring step is as important as the design and printing processes, and an insufficient postcuring time can result in dimensional  
Figure 8: Overall deviations of denture bases produced using the MAZIC D resin and Phrozen Shuffle 3D printer presented as color maps. Deviation range of \(\pm\)500 μm and a tolerance of \(\pm\)50 μm was set. changes or reduced strength due to the presence of unpolymerized resin [28]. If the output is an individual tray, insufficient postcuring may result in distortion of the tray and the impression body after obtaining the impression. In the case of a denture base, insufficient postcuring may cause issues relating to its fit, which affects the accuracy of the artificial tooth attachment due to warping of the joint, and may, in turn, lead to an overall occlusal error. In addition, even for a three-dimensionally printed model, insufficient postcuring can lead to errors in the fabrication of the prosthesis that cause serious problems [29]. In the present experiments using the MAZIC D resin and the DLP-type Phrozen Shuffle 3D printer, dimensional changes during postcuring were hardly observed in the group with the support structure present. However, in the group where the support structure was not present, a rapid change in dimensions was observed during the first 15 min of postcuring. As mentioned above, this is considered to be due to a problem with the initial polymerization rate. Additional changes may have occurred due to the presence of bulk resin in the palate area and the direction of polymerization shrinkage in this direction.