Distributed optical fiber sensor technology for bite force mapping

Measuring bite force gives important information about the performance of the jaw muscles. Enhancement of bite force measurements, particularly 2D force mapping, can be achieved through the application of advanced distributed fiber optics sensing techniques, which present the capability to acquire high resolution measurements. Optical Backscatter Reflectometry (OBR), based on the principles of Optical Frequency Domain Reflectometry (OFDR), is the key to achieve spatially distributed measurements and transform a single-mode fiber (SMF) into a cost-effective minimally invasive sensor. The OBR interrogator, manufactured by LUNA, catches the light backscattered by each section of the fiber and detects the spectral variation induced by the stain and pressure application. We have developed two methods to construct a two-dimensional map of the applied bite force. In the first a SMF has been bent into four lines and embedded into a silicone mouthguard. In the second approach we used massive Scattering‑Level Multiplexing (SLMux), which exploits fibers with different scattering levels: a standard low scattering SMF to enable the multiplexing, and a MgO‑nanoparticles doped fibers with a 40 dB higher scattering for sensing purposes. The setup with eight multiplexed fibers allows to obtain bite force mapping for each side of the jaw by embedding four fibers for left and right sides. The pressure sensitivity coefficient of the maps has been effectively calculated. The setup has been validated for 2D force mapping over the silicone mouthguard with millimeter resolution. The capability of optical fiber to be multiplexed and embedded in non-uniform geometries results in a high resolved and precise 2D bite force reconstruction.