A fiber Bragg grating-based method for measuring mesiodistal tooth displacement and force under physiological conditions

Objectives This study aims to establish a system for measuring mesiodistal tooth displacement and force via fiber Bragg gratings (FBGs) and investigate its stability and feasibility via experiments on both models and healthy volunteers. Methods The system was established using an FBG sensor and decoder. The FBG sensor was embedded into an 0.018×0.025 NiTi Archwires (Heat-activated Archwire SM Rectangular, Innovative Material and Devices, Inc., China) and placed on the brackets of the upper incisors. The micro shift of teeth led to the bending of the FBG fiber and a consequent wavelength shift. The shift was exported to the deformation of teeth by the decoder. In the in vitro test, a dynamometer was used to load known vertical forces on the model, the mobility was tested, and the mesiodistal tooth displacement and force were measured. In the in vivo test, biting and chewing tests for hard, medium, and soft foods were conducted with two volunteers. The mesiodistal tooth displacement and force were calculated based on the Bragg wavelength shift. Results In the in vitro experiment, when a force of 1 N was applied vertically on the model, the strain deviation of the FBG sensor was 8.56 ± 2.83 µε, the consequent mesiodistal tooth displacement was 0.068 ± 0.023 µm, and the mesiodistal force was 0.200 ± 0.067 N. A linear relationship was observed between the loading force and both tooth displacement and force in the mesiodistal direction. In the in vivo experiment, the two subjects showed different biting and chewing patterns, and the mesiodistal tooth displacement and force showed large differences when biting foods with different hardness levels. Conclusions The established FBG-based system enabled the measurement of mesiodistal tooth displacement and force under physiological conditions, effectively capturing the dynamic biomechanical interactions during orthodontic processes. This provides a reliable tool for obtaining quantitative data directly from the oral environment. Clinical Relevance: This research provides a novel FBG-based method for measuring mesiodistal tooth displacement and force in vivo, informing the physiological and pathological conditions of teeth.