First Telemetric Smart Orthodontic Bracket for Therapeutic Applications

This paper reports a telemetric orthodontic bracket instrumented with a CMOS stress sensor chip which makes it possible to measure the 3D force and moment vectors acting on individual teeth. For the first time, this sensor system was equipped with the slot component of a standard ceramic bracket and was telemetrically read out over a distance sufficient to allow contactless operation in orthodontic applications. The maximum distance between the external reader coil and the microcoil within the bracket is 2.4 mm. The minimal transferred power to keep the system in operation is 17 mW. The 2×2.5-mm
²
-small Cu microcoil is embedded in SU-8, comprises 35 windings and is 22 μm in height. A reader unit which maximizes the transferable power while simplifying the electronic equipment was designed. The reader coil was tuned to resonance at 13.56 MHz in agreement with the ISM band reserved for medical RFID systems. The telemetrically extracted sensor data are demodulated, digitized and decoded by the reader unit, which is connected to a graphical user interface. Force and moment values were successfully measured with resolutions better than 60 mN and 0.14 Nmm, respectively.