## 4 Discussion  
An autonomous robot osteotomy scheme was developed and demonstrated with direct coordinate determination by three points on the teeth. The accuracy of our autonomous robotic osteotomy system was evaluated on both stone models and mandible phantoms. Some researchers reported that the RMS differences for an optical navigation between the planning and postoperative computed tomographic model were 1.31 \(\pm\) 0.28 mm and 1.74 \(\pm\) 0.73 mm, respectively [12]. In another study using skull fiducial or laser registration, the results had a 1.75 \(\pm\) 0.94 mm radial error, 2.82 \(\pm\) 1.1 mm depth error, and 3.39 \(\pm\) 1.078 mm target point error [13]. In our system using direct coordinate determination, the position, length, angle, and depth errors were 0.93 \(\pm\) 0.45 mm, 0.81 \(\pm\) 0.34 mm, 1.26 \(\pm\) 1.35\({}^{\circ}\), and 1.19 \(\pm\) 0.73 mm, respectively. Although the angle and depth errors were larger than the position and length errors, our system was accurate compared to autonomous robot studies using other registration methods. Figure 7: Test for the ease with which the posterior mandibular ramal area could be approached by the robot arm osteotomy through an intraoral approach in the dummy operating theater: inferior cut with 20 mm disc (**a**) and 6 mm disc (**b**), and superior cut with 6 mm disc (**c**). At the posterior and anterior cuts, robot osteotomy was designed such that the fissure bur was sliding in the model by 5 mm as the depth of RBG design. The length error represented the accuracy of this action. Moreover, at the inferior and superior cuts, the 20 mm diameter disc saw moved into the model with a 5 mm depth and a slide with 20 mm length. Depth error represented the accuracy of how deep the disc moved into the model. These depth and angle errors were quite large compared with the position and length errors. The position error is position-dependent when the robot arm moves without any resistance, but the depth errors are affected by the changing resistance depending on the density of the model, which corresponds to bone in an actual patient. Therefore, the depth error tended to be larger than the other errors. The control of angular deviation is a different issue from positioning the end point. Our results demonstrated that the angular control of the end effector could be more difficult than position control. In 1991, [PERSON] et al. performed the first orthopedic surgery for hip replacement using the ROBODOC surgical device, which was the first system that could implement a preplanned milling trajectory [14]. In oral and maxillofacial surgery, the first application of robot-assisted surgery was by [PERSON], who performed preclinical tests of antrostomy using the ROBODOC system [15]. In 1998, the OTTO system (Surgical Robotics Laboratory, Medical Faculty Charite, Humboldt-University, Berlin, Germany) was developed as the first interactive robotic system for positioning an electric drill in maxillofacial surgery [16]. To the best of our knowledge, no robotic system has been specifically designed for crani-maxillofacial reconstruction, particularly in hard tissue surgery [6]. In particular, there are no commercially available robots in the oral and maxillofacial surgery field, and there are not many ongoing studies. Six levels of autonomy for medical robotics were proposed as one possible framework. (Level 0: No autonomy, Level 1: Robot assistance, Level 2: Task autonomy, Level 3: Conditional autonomy, Level 4: High autonomy, and Level 5: Full autonomy) [17]. Robot-assisted surgery and robot-guided surgery belongs to Level 1, Robot assistance. Our robot arm belongs to Level 2, Task autonomy, as it can partially perform tasks automatically. This study is a new attempt to use an autonomous robot in the maxillofacial region and goes one step further to a higher level of autonomy. Mandible RBG osteotomy on a phantom model was performed successfully. There was no significant difference between the 6 mm disc group and the 20 mm disc group during both robotic and manual surgery.