Thermomechanical Comparison of PET-G and TC-85 Orthodontic Aligner Materials

This study combined thermomechanical characterisation with finite element analysis to compare polyethylene terephthalate glycol (PET-G) and Tera Harz TC-85 orthodontic aligner materials. Tensile properties were evaluated at 23, 37, 55 and 80 °C, with five observations per material and temperature. Identical full-arch geometries with a nominal thickness of 0.75 mm were subjected to 600 N compression at 300 K, heating under maintained load to 352 K and cooling to 310 K. At 23 °C, tensile moduli were 1396.4 ± 44.9 MPa for PET-G and 675.4 ± 21.2 MPa for TC-85. Dynamic mechanical analysis (DMA) loss-tangent maxima occurred at sampled temperatures of 80 and 45 °C. Tensile and DMA moduli diverged at elevated temperatures. Initial maximum effective strains were 0.165 and 0.196, and medium-to-fine mesh changes were 1.78% and 2.61%. TC-85 showed a greater reduction in maximum strain following heating to 78.85 °C. Recovery benchmark values at 60 min were 63.3% for PET-G and 92.5% for TC-85; paired-series metrics quantified curve agreement. PET-G exhibited higher tensile stiffness, whereas TC-85 exhibited greater benchmark recovery and a larger thermal-stage strain reduction. The high-temperature endpoint represents ex vivo activation. Constitutive and experimental limitations constrain extrapolation to clinical appliance performance.