Comparison of Different Thermoplastic Materials by View of Elastic Energy

Objectives: The development of thermoplastic aligners in the field of orthodontic treatment has been ongoing for several decades. The mechanical properties of these thermoplastic materials, primarily hardness and elastic modulus, are closely related to the biomechanics and principles of tooth movement. This study aims to investigate the material properties of commercially available clear aligners and compare their elastic energy using nano-indentation technology.
Methods: Two commercially available thermoplastic materials (BenQ and Invisalign) were thermoformed, embedded, and polished to prepare samples. Measurements were conducted using the MTS Nano Indenter XP system, analyzing a 9-point array for elastic modulus, hardness, and elastic energy. FTIR was performed to identify functional groups, and SPSS was used for statistical analysis.
Results: FTIR results indicated differences in material composition and bonding between BenQ and Invisalign. The elastic modulus and hardness of Invisalign were 2.30 ± 0.21 GPa and 0.12 ± 0.02 GPa, respectively, while BenQ showed 2.70 ± 0.30 GPa and 0.11 ± 0.04 GPa. Significant differences (P < 0.05) in elastic modulus were observed between active and non-active regions of Invisalign, though hardness showed no statistical difference. Elastic work calculations revealed 23.92 nJ for BenQ and 21.92 nJ for Invisalign. Additionally, Invisalign's elastic work was lower in regions with active and non-active regions. Subdivision into early and late orthodontic stages showed greater elastic work in the late stage for both active and non-active regions.
Conclusions: This study found that while Invisalign and BenQ differ in material composition, their elastic modulus and hardness show no significant statistical differences. However, Invisalign’s elastic modulus varies significantly between active and non-active tooth regions, though hardness does not. Additionally, elastic work differs between early and late orthodontic stages and between active and non-active regions, offering valuable insights into orthodontic biomechanics.