3D force measurement with an open source/DIY load-cell: Setup, precision and application in aligner orthodontics

Background: In aligner orthodontics the relationship be- tween movement per step, material properties and generated forces is not immediately obvious. In complex cases, the attachment level of periodontally impaired teeth as well as the attachment shape and position must also be considered. Thus, one way to learn more about these conditions is to gain experience from daily clinical practice, the other way is to examine various situations in vitro. In the course of scientific investigations, several sophisticated devices have been developed using high-precision industrial three-axis force and moment sensors. The high costs of the sensors and the complexity of the interaction between software and hardware constitute an obstacle for extensive use in the educational area. Objective: To develop a low-cost sensor system for orthodontic force measurement for educational purposes. Material and methods: A simple, open source apparatus for three-axis force measurement using load cells is presented here. Comprehensive information about software and hardware as well as details about measurement quality are also presented. Additionally, an example illustrating the results derived from an experimental setup with intrusion/extrusion of a central incisor is also given. Results: The results of the calibration process and error measurement showed that it was possible to assemble an adequately accurate (ICC ≥ 0.999) device. The Dahlberg error was under 0.3 g, sensor readouts were linear and repeated measurements were accurate enough for the desired purpose. The measurement example demonstrated that it was possible to simulate a clinical situation. Conclusion: The presented apparatus may be a good starting point for further educational projects. Keywords: 3D printing, aligner, DIY, force measurement