A Wireless Stress Mapping System for Orthodontic Brackets Using CMOS Integrated Sensors

A wireless stress mapping system for the development of “smart brackets” is presented. The system is designed for monitoring the forces and moments applied to individual teeth during orthodontic therapy which may contribute to improve treatment effectiveness. It comprises a stress mapping chip fabricated in a 0.35-μm process and a micro coil produced by gold electroplating in a photoresist mask. Twenty-four transistor-based stress sensors for measuring either in-plane shear stress or the difference of in-plane normal stresses are strategically distributed over the chip area. The sensor signals are processed by a variable-gain differential difference amplifier and digitized by a 10-bit SAR ADC, enabling a resolution down to 11 kPa at highest gain. A wireless interface conditions the energy received at 13.56 MHz and transmits the data by load modulation. With dimensions of 2 × 2.5 × 0.73 mm
³
and a power consumption of 1.75 mW, the system lays the foundation for the assembly of smart brackets as innovative tools in orthodontic therapy.