## 2 Materials and Methods  
A typodont model (Nissin, Kyoto, Japan) was scanned using a desktop scanner (Identica hybrid, Medit, Seoul, Republic of Korea), and was saved as a standard triangle language (STL) file. The direction and position of a miniscrew was determined using custom-developed software, and the miniscrew was placed between the estimated roots of the second premolar and the first molar. The 3D models of surgical guides were generated by thickening a part of the typodont model and subtracting the original model. The undercuts of the model were removed so that the surgical guide could be removed after the placement. The surgical guide was designed to cover the first premolar and the first molar. The length of this part was set at 2.0 mm. The guide hole for the drilling of the 1.0 mm diameter was placed in the planned position. Three different lengths were tested for this part, namely, 3.0, 4.5, and 6.0 mm. A higher level of accuracy was expected with a longer guide (Figure 1). The 3D models of the surgical guides and the typodont were printed using a digital light processing (DLP) 3D printer (ASIGA MAX UV, Asiga, Alexandria, Australia) and a clear resin (DentaGUIDE, Asiga, Alexandria, Australia). A layer thickness of 0.1 mm was used for the printing configuration. Five surgical guides were printed for each length. Thus, 15 surgical guides were printed for the test. The drilling tests were performed on duplicated typodonts (Figure 2). The part of the typodont model, which was close to the surgical guide, was extracted and duplicated using the same 3D printer and an accurate resin for the dental model (DentaMODEL, Asiga, Alexandria, Australia). We printed 20 duplicated typodont models. A layer thickness of  
Figure 1: The design of the surgical guide. The second premolar was partially exposed to check the fitting to the teeth. The length of the surgical guide is the distance from the gingival surface to the top of the guide tube. 0.05 mm was used to print the models. The surgical guides were placed on the duplicated typodont, then the holes were drilled using a micro-motor (Ultimate XL, NSK Nakanishi, Tochigi, Japan) at 1000 rpm. The drill was a double flute drill of 1.0 mm made of high-speed steel (PROXXON, Osaka, Japan). Drilling without using surgical guides (freehand drilling) was also performed as a reference. The drilling depth was set to be 6.0 mm. After the drilling, the surgical guides were removed, then the drilled typodonts were scanned to make 3D surface models. All typodonts were scanned using micro-computed tomography (micro-CT) (R-mCT, Rigaku, Tokyo, Japan). The voxel size and voltage of the X-ray tube were 50 \(\upmu\)m and 90 kV, respectively. The volume data of the micro-CT were exported in a Digital Imaging and Communications in Medicine (DICOM) format and converted to 3D surface data using the marching cubes algorithm. The 3D surface model of the drilled typodont was superimposed onto a reference model to evaluate the accuracy of the drilling (Figure 3A). The surface data of the original typodont model were used as a reference, and the superimposition was calculated by using the iterative closest-point algorithm with custom-developed software. After the superimposition, we measured the distance from the opening of the hole to the ideal insertion vector, the distance from the bottom of the hole to the ideal insertion vector, and the angular difference between the drilled direction and the ideal insertion vector (Figure 3B). Figure 3: (**A**) The superimposition of the original typodont model and the reconstructed surface data from the micro-CT image. (**B**) The yellow line shows the ideal insertion vector, and the red line shows the actual direction of the drilled hole. Distance 1 is the distance between the ideal path and the bottom of the actual hole. Distance 2 is the distance between the ideal path and the opening of the actual hole. The angle between the yellow line and red line was also measured. Figure 2: (**A**) The partial typodont model extracted from the original model.