RF energy harvesting for intraoral orthodontic force monitoring

Optimal orthodontic forces need to be applied to induce appropriate biological and mechanical reactions in the periodontium, thus leading to proper tooth movements, while excessive orthodontic forces could harm the tooth roots and periodontal tissues during treatment. However, estimating orthodontic forces currently relies on clinical experience, lacking objective data and analysis; thus monitoring the in-vivo orthodontic force is essential to reducing side effects and improving orthodontic treatment. Unfortunately, in-vivo orthodontic force sensor systems are currently not available, and in-vitro ones are mostly bulky and costly. Here, we report a battery-free and wireless orthodontic force sensing system (BWS) designed for in-vivo, contactless, and real-time measurement of the orthodontic force. We developed a 915 MHz far-field RF energy harvesting system to power the intraoral BWS, and achieved an in vivo wireless measurement distance of 220 mm. This system allows in-vivo orthodontic force monitoring at anytime and anywhere, so it can be applied to improve clinical treatments and orthodontic research. Besides, in vivo experiments demonstrate that the system can harvest a voltage of 2 V even at a 350 mm distance, which highlights the device's potential to serve as a versatile platform for monitoring various oral environmental parameters through different sensors.