Telemetric smart orthodontic brackets

Abstract: This thesis reports the development, fabrication and characterization of a telemetric smart orthodontic bracket. The telemetric smart bracket comprises a previously developed CMOS chip equipped with 32 integrated piezoresistive field effect transistors (piezo-FETs), a microcoil for the real- ization of an inductive link and a reader unit for the telemetric readout. The piezo-FETs on the CMOS chip produce a voltage signal proportional to the applied mechanical in-plane normal stress, which is amplified and digitized on-chip. The CMOS chip, which is electrically connected to the hybridly manufactured microcoil, is powered via the electromagnetic field provided by the reader unit. As long as the chip is powered, the piezo-FETs continuously provide a signal proportional to their mechanical stress values. These signals are transmitted over the inductive link between the antenna of the reader unit and the microcoil using the principle of load modulation. In total, three smart bracket versions have been developed in this thesis. All three versions are smaller than 2 mm x 2.7 mm x 0.7 mm Version 1 comprises a planar microcoil, which connects to the CMOS chip using flip chip bonding. The manufacturing process of this microcoil has been developed in this thesis and is based on copper electroplating into a 35 µm thick photolithographically structured resist. The achieved coil track dimensions measure only 5 µm in width, 22 µm in height, with a spacing of 10µm between their tracks. Using a special process step for structuring of the seed layer, the seed layer between the coil tracks is etched away selectively, which results in a higher process reliability since the thin copper coil tracks are not attacked. Since copper was selected for the microcoil tracks, the serial resistance could be minimized to approximately 7-30 Ohms depending o the number of turns and track dimensions. The assembly with the CMOS chip was attached to a ceramic bracket and readout telemetrically up to a coil-to-coil distance of 3-3.9 mm, depending on the tuning state of the reader unit. This configuration allows for the first clinical tests using a rubber ligature and a metallic arch wire. However, the use of metallic ligatures could not be realized due to insufficient magnetic coupling. In order to improve the magnetic coupling of the reader unit to the smart bracket, version 2 comprises a second type of microcoil. The applied micro- coil was integrated onto the CMOS chip using an automatic wirebonder, winding a 25 µm-thick insulated copper wire around a cylindric SU-8 post glued on the CMOS chip. Due to the helical geometry of this microcoil, the coupling and the transmission distance was significantly improved in simulations and measurements. The achieved transmission distance was increased to 5-6 mm. This range depended mainly on the tuning of the reader unit and the surrounding metallic materials. The coupling factor at a distance of 3 mm was 4% in the measurement and 3.5% in the simulation. Due to the increased coupling factor, a smart bracket ligated to the arch wire with metallic ligatures could be read out for the first time. However, the SU-8 manufacturing process turned out to show height variations of up to 100 µm for a desired height of 400 µm, thus lowering the yield of the winding process. Furthermore, the mechanical properties of the rather soft SU-8 are unsuitable for the final integration of the smart bracket. In order to improve the mentioned disadvantages of the SU-8 posts in version 2, a third version of the smart bracket was developed. Therefore, the posts from version 2 were replaced by laser-cut ceramic posts with a rectangular shape. Since they were cut from a single ceramic wafer, height variations were practically eliminated.Round edges and the negative angle caused by the laser profile helped improve the winding yield up to 70-90% depending on the ultrasonic power drift of the wirebonder. All three smart bracket versions are suitable for clinical experiments thanks to the reader unit and the optimized antenna, developed in this thesis. The smart brackets have experimentally proven their capability of measuring the 6DOF loads with a uncertainty of 28-707 mN for the forces and 0.063- 0.652 Nmm for the moments

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Universität Freiburg, Dissertation, 2022

Klassifikation und Themen

• Schlagwort: CMOS ; Implantiertes medizinisches Gerät ; Mikrosystemtechnik ; Sensor ; Kieferorthopädie

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2022
• Urheber: Hafner, Julian
• Beteiligte Personen und Organisationen: Paul, Oliver ; Reindl, Leonhard M. ; Albert-Ludwigs-Universität Freiburg. Fakultät für Angewandte Wissenschaften

Weitere Informationen

• DOI: 10.6094/UNIFR/229298
• URN: urn:nbn:de:bsz:25-freidok-2292986
• Rechteinformation: Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 15.08.2025, 07:38 MESZ