The Periodontal Ligament (PDL) is a soft connective tissue that anchors the tooth to the surrounding alveolar bone, forming a tooth-PDL-bone complex (TPBC). The PDL demonstrates nonlinear, viscoelastic, anisotropic, and heterogeneous mechanical material properties that facilitate in protection and adaptation of the TPBC against external loads. The PDL will act as a shock absorber to protect the TPBC against high magnitude loads, such as mastication. The TPBC can adapt in response to long-term low magnitude load conditions, such as those applied through orthodontic appliances, as the stress/strain state within the PDL can trigger a cellular biological response leading to alveolar bone remodelling and, subsequently, tooth movement. Determining the PDL’s mechanical material properties and its stress/strain response to applied loading is critical to understanding its behaviour and biological implications. Due to the small and varying geometry, direct mechanical measurements from an intact PDL are limited. An in-fibre Bragg grating (FBG) sensor is a small and flexible sensor that can be placed within the PDL space of an intact TPBC and measure repeatable strains. The repeatability of sensor measures within a single TPBC has been demonstrated in previous works. However, the repeatability, sensitivity, reproducibility, and verification of measurements has yet to be evaluated.

The objectives of this work were to first define an apically directed, quasi-static, displacement-controlled experimental protocol to obtain force, displacement, and FBG strain measurements from an intact TPBC. Second, a cross-verification between FBG strain measures obtained using the defined experimental protocol and a finite element model was used to determine the relationship between FBG and finite element strain measurements.

A rigorous investigation of the repeatability, sensitivity and reproducibility of output FBG strains from within the PDL space and reaction force measurements was completed. It was concluded that:​ the experimental protocol was repeatable within, but not across, TPBCs;​ the output measures were highly sensitive to experimental protocol input parameters;​ and the force and strain measures were reproducible when replacing an FBG within a TPBC. Using the defined experimental protocol, a cross-verification between strain magnitudes from a representative finite element model and FBG strain measurements suggested a one-to-one comparison was not appropriate. However, a statistically significant linear relationship was found for the change in strain induced by varying tooth displacement between experimental and finite element model outputs, suggesting the FBG is capable of predicting a change in the PDL strain.

The results of this thesis showed that the FBG could be replaced within a TPBC and measure a representative change in strain with varying tooth displacements. Therefore, the proposed FBG method has potential applications within in vivo studies where the mechanical properties of an intact PDL are to be monitored over time, eliminating the need to sacrifice specimens to isolate the PDL for mechanical measurement. This could be implemented to advance literature focused on treatment protocols within a diseased or injured PDL or for optimization of orthodontic treatments.