Effects of Thermoforming and Intraoral Aging on Mechanical Properties of Three Different Commercially Available Orthodontic Aligners: A Prospective Clinical Study

Aim: This study aimed to evaluate the effects of thermoforming (TF) and intraoral aging (IOA) on the mechanical properties of three commercially available orthodontic aligners made from two material types, polyethylene terephthalate glycol (PETG) and polyurethane (PU).Materials and methods: Aligner sheets made of PETG (Erkodur), PETG (Taglus), and PU (Zendura), each with a uniform thickness of 0.75 mm, were thermoformed using a Biostar Thermoforming Machine.These thermoformed aligners were then delivered to 15 orthodontic patients (five patients per material group) who wore them continuously for 2 weeks.Mechanical properties, including surface roughness, hardness, and flexural modulus, were assessed at three time points: (T0) as-received, (T1) post-TF, and (T2) post-IOA.Surface roughness was analyzed using an optical profilometer, hardness using a micro-Vickers hardness tester, and flexural strength (FS) using a universal testing machine (UTM).Statistical analysis was performed using SPSS 23.0 with Kruskal-Wallis and Friedman's tests (p < 0.05).Results: Erkodur (PETG) exhibited the highest increase in surface roughness post-IOA (p = 0.015).Taglus (PU) demonstrated the highest hardness throughout (p < 0.05), increasing further after IOA (p = 0.029).FS was highest in Taglus (PU) at baseline and after TF, but Erkodur (PETG) showed the highest FS after IOA.Significant alterations in all three mechanical properties were observed across the aligners at different time points.Conclusion: Thermoforming and IOA significantly affect aligner mechanical and surface properties.PETG aligners exhibited higher surface roughness after intraoral aging, while PU aligners showed higher hardness both before and after TF and after aging.FS reduced considerably in PU aligners after aging, whereas it increased in PETG aligners.Clinical significance: Understanding the effects of TF and IOA on different aligner materials provides valuable insight into their long-term mechanical performance, enabling clinicians to make evidence-based choices for material selection.This ensures better force delivery, durability, and treatment efficiency during clear aligner therapy (CAT).