# Four Different Build Angles in 3D-Printed Complete Deture Bases: A Comparative In Vitro Study
## 4 Discussion
Consistent with previous studies, the mean RMSE was the smallest in 3D-printed prostheses with a build angle of approximately 90\({}^{\circ}\)[12; 18; 35]. However, based on our color difference map, denture bases with a 90\({}^{\circ}\) build angle did not demonstrate clinically better tissue adaptation across the overall surface compared to denture bases with other build angles, similar to the results reported by [PERSON] et al. [18]. This is primarily because the negative deviation at the posterior palatal seal region decreases the retention of the denture base. In contrast to our study, [PERSON] et al. used a DLP 3D printer and adjusted the build angles by lifting the posterior part of the denture base; they showed clinically better tissue adaption at the posterior region of the denture base [27]. However, across all build angles, the range of error values between the digital model and the denture base tissue surface was as follows: RMSE ranged from 220 to 290 \(\upmu\)m, mean positive deviation (impingement) ranged from 130 to 220 \(\upmu\)m, and mean negative deviation (misfit in space) ranged from \(-227\) to \(-133\)\(\upmu\)m. All these values were within the clinically acceptable range [20]. Unlike previous studies that showed significant differences in the distance between bilateral amines and molars in denture bases with different build angles [18], our results did not show differences in the inter-canine width and inter-molar width  
The inter-AP lengths were not significantly different between denture bases with 0\({}^{\circ}\) and 30\({}^{\circ}\) build angles or between those with 60\({}^{\circ}\) and 90\({}^{\circ}\) build angles. However, compared to the denture bases with 0\({}^{\circ}\) and 30\({}^{\circ}\) build angles, those with 60\({}^{\circ}\) and 90\({}^{\circ}\) build angles exhibited a significantly greater inter-AP length. This observation aligns with the differences in adaptation between the digital model and the denture base tissue surface in the anterior and posterior regions, as illustrated by the color difference map. As the build angle increases, notable changes in adaptation are observed in both the anterior palatal rugae area and the posterior border seal area of the denture base. The primary reason for this is that the posterior border seal area, which is printed first, is more susceptible to tensile forces and gravity, which increases as the build angle rises. Consequently, this area is more prone to deformation at higher build angles. Additionally, at higher build angles (60\({}^{\circ}\) and 90\({}^{\circ}\)), tissue adaptation in the anterior palatal rugae region tends to show a positive deviation. This effect may result from the best-fit algorithm used in Geomagic Control(r), which aims to minimize overall deviation when significant deformation occurs in the posterior border seal area of the denture. The average of the error values for all build angles was within clinical limits. However, the error values for the distances between the polished surfaces of the denture bases ranged from \(-2.14\) mm to \(+2.28\) mm, which exceeds the error range typically observed in dentures produced using the conventional heat-curing process [2]. This is thought to be a result of additional errors incurred while modifying the positions of the automatically generated supporters around the reference points of the denture base's polished surface in the 3D printer slicing program, which may have had an impact on the precision in that area [36]. Additionally, manually identifying and measuring the length between the reference points, which were set in the CAD model for the 3D-printed dentures, could have caused this result. Thus, a method for assessing the accuracy of the polished surface that incorporates a supporter for 3D printing is needed. In SLA or DLP 3D printing, the build angle refers to the orientation in which the object is sliced during the printing process [32].