Page 75 - Demo

4Robot technology in analyzing tooth removal, a proof of concept73believe that, especially when using fresh frozen cadavers, the setup can be used to gain a unique and relevant new insight into tooth removal techniques.Mechanically the development of the rigid fixation method for a human upper and, to a lesser extent, lower jaw was most challenging. Several designs were 3D-printed in plastic and tested on conserved cadaver jaws on ease-of-fixation and rigidity of the fixation method before the final design was chosen and manufactured in stainless steel. When first testing the stainless steel setup a slight mobility of the jaw holders was noted due to the locking bolt in the rotational plate, which was a prefabricated and gave some slack. It was later customized to a locking pin that could be tightened by rotation, which resulted in a strong and complete rigid fixation of the jaws. During the experiments with fresh frozen jaws, out of 146 experiments, only 2 times an experiment failed because of loosening of the jaw within the holding device. Both times, it involved an upper jaw and loosening was due to improper tightening of the holding device at the start of the experiment.For the measurement of movements, a robot was added to the setup. One of the major concerns when using the robot in a ‘compliant’ mode was the robot not being fully passive at all times. Especially when joint limits are approached with some pace, the robot showed resistance when adapting its joint position to enable certain positions or movements. To overcome this problem a ‘best fit’ starting position of the end-effector of the robot was to be found where most (relevant) joints were in a neutral position to ensure as little resistance as possible. Although it is difficult to measure the exact value of the resistance, it seems relatively small in comparison with the large amounts of forces exerted. The upper jaw was fixated with the occlusal plane in a vertical way and the lower jaw with its occlusal plane horizontal to mimic the clinical situation, which required different “preset” joint positions for upper and lower jaws. These positions, that were optimized based on preference from the surgeons, were programmed starting position for all experiments. The combination of an adjustable frame and a rotational plate ensured roughly the same starting position for all experiments in upper and lower jaw. Pre-programming the same joint positions at the start of each experiment also added to the reproducibility of the experiments. Despite all efforts on creating a setup that comes as close to a clinical setting as possible, it must be noted that some resistance seems inevitable and this should be taken into account when interpreting results of these experiments. Despite a slight learning curve was noted Tom van Riet.indd 73 26-10-2023 11:59