Development of a Periodontal Ligament Simulant for in-vitro Studies

Objectives: The use of in-vitro experimental methods to investigate orthodontic appliances/procedures is widely debated in the literature, namely due to the lack of periodontal ligament (PDL) compliance. The objective of this study is to develop a simulated tooth/PDL/bone complex (TPBC) that replicates the true initial response to loading.
Methods: Simulated TPBC’s were constructed by manufacturing separate single-rooted tooth and socket pieces using aluminum. Root geometry was chosen to match the approximate height and width of a central maxillary incisor, and was conical in shape. PDL simulant was formed by mixing equal parts of silicone (587 Blue RTV Silicone, Loctite®, Westlake Ohio USA) and gasket sealant (2, Loctite®, Westlake Ohio USA). PDL thicknesses ranging from 0.2-0.7mm, in increments of 0.1mm, were tested to determine geometry that best replicates true TPBC response to loading. A sample size of 5 was used for each thickness. To observe the simulated TPBC’s response to displacement, a digitally-controlled micrometer (PI M230.10, PI, Auburn, MA, USA) was used to apply a linear displacement to the simulated tooth. Displacement was applied in the occlusal plane at a rate of 0.001mm/s up to 0.2mm, and at a distance of 10.3mm from the gingival crest of the simulated TPBC to replicate in-vivo experiments from the literature. A six-axis load cell (Nano17, ATI Industrial Automation, Apex, NC, USA) measured the resulting force during loading.
Results: In comparing the force-displacement response of the simulated TPBC’s to data from the literature, it was determined the 0.5mm thick PDL layer yielded the best response. Its force-displacement behavior closely emulated the trends and magnitudes observed from existing data.
Conclusions: A simulated TPBC has been developed and validated using true force-displacement data from the literature. This model can now be used in future in-vitro studies when considering initial tooth movement during orthodontic treatment.