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Thermoformed versus directly 3D-printed clear aligner materials: A comparative in vitro study of thermomechanical
Bismina Noushad1, Achint Juneja1, Monis Raza1
1Department of Orthodontics and Dentofacial Orthopaedics, Institute of Dental Studies and Technologies (IDST), Modinagar, Uttar Pradesh, India.
Objective:
To compare thermoformed polyurethane aligners (Zendura®) and directly 3D-printed shape-memory aligners (TC-85™) in terms of thermomechanical behaviour, chemical extractables, and shape-recovery performance.
Material And Methods:
In this in vitro comparative study, standardized specimens (n=22/group) were evaluated using differential scanning calorimetry (Tg, ΔCp), gas chromatography-mass spectrometry (ISO 4049 extractables), and shape-recovery testing at multiple temperatures; time-dependent stress relaxation under constant strain (2% tensile strain, 180min, 37°C) was additionally evaluated as a viscoelastic measure of orthodontic force decay. Measurements were recorded at baseline and after 7 days of artificial saliva ageing. Statistical analysis was performed using parametric and non-parametric tests (P≤0.05).
Results:
Both materials showed increased extractables after ageing (P<0.05). Zendura exhibited significantly higher cumulative extractables than TC-85™ (P<0.001). ΔCp remained stable in both groups, with higher values in TC-85™ (P<0.001). Tg remained stable for Zendura but decreased slightly for TC-85™ (P=0.043), with TC-85™ demonstrating lower Tg overall (P<0.001). Shape recovery decreased after ageing in both materials but remained significantly higher in TC-85™ (P<0.001). Under constant strain, TC-85™ underwent significantly less stress relaxation than Zendura® (27.2±0.5% vs. 41.3±0.4%; P<0.001) and retained a higher residual force at 180min (72.8% vs. 58.7%), indicating more sustained force delivery in vitro.
Conclusion:
Directly 3D-printed TC-85™ aligners demonstrated lower extractables, favourable thermal properties, greater resistance to stress relaxation, and superior shape-recovery behaviour compared with thermoformed Zendura® under short-term ageing conditions. These differences reflect material behaviour under standardized bench conditions and should not be interpreted as direct evidence of superior clinical force delivery or biocompatibility.
