HARDNESS AND ELASTIC MODULUS ASSESSMENT FOR TWO ALIGNER MATERIALS BEFORE AND AFTER THERMOCYCLING: A COMPARATIVE STUDY

Clear aligners have gained popularity as an alternative to traditional orthodontic appliances. Yet, the long-term mechanical behavior of aligner materials under thermal stress remains understudied. While prior research has established that thermoplastic materials undergo property changes with temperature, the specific effects of thermocycling on hardness and elastic modulus have not been fully resolved. This gap motivated the current investigation into how two commonly used thermoplastic materials respond to simulated oral conditions. No prior work had resolved the comparative durability of these materials after repeated thermal exposure. Understanding these properties is essential for predicting clinical performance. The need for accurate mechanical data has grown with increasing use of aligners. This study aims to address that need by focusing on material behavior under thermocycling. The findings could help clinicians choose materials that maintain performance over time.

The study aimed to evaluate how thermocycling affects the mechanical properties of two thermoplastic materials used in orthodontic aligners. Specifically, it focused on hardness and elastic modulus as key indicators of material performance. The motivation comes from the growing use of aligners and the lack of data on material behavior under thermal stress. The goal was to compare two specific products: Duran® and Erkodur®. The researchers wanted to determine if thermocycling alters these properties significantly. They also sought to identify which material is more stable under repeated thermal changes. The study was designed to provide data that could inform material selection in clinical settings. By measuring properties before and after thermocycling, the study aimed to simulate real-world usage conditions.

The study used two thermoplastic materials: Duran® and Erkodur®. For hardness testing, disk-shaped samples were 3D printed to standard dimensions and thermoformed into sheets. Twenty samples were tested for each material. Shore D hardness was measured before and after thermocycling. For elastic modulus, dog bone-shaped resin specimens were 3D printed and tested using tensile methods. The testing protocols followed ASTM D882-02 and ASTM D638-02a standards. Thermocycling was simulated using a controlled temperature protocol to mimic oral conditions. A universal testing machine was used to measure elastic modulus under tension. The study compared results between the two materials and before/after thermocycling.

Erkodur® showed higher hardness than Duran® before and after thermocycling. However, Erkodur® experienced a significant decrease in hardness after thermocycling, while Duran® remained stable. The elastic modulus of Duran® was consistently higher than Erkodur® in both pre- and post-thermocycling conditions. Thermocycling had no significant effect on the elastic modulus of either material. The difference in hardness between the two materials was statistically significant. The lack of change in elastic modulus suggests both materials retain structural integrity. The findings indicate that material choice may influence long-term performance. These results provide insights into how aligner materials behave under thermal stress.

The authors concluded that Erkodur® has higher initial hardness than Duran® but is more affected by thermocycling. Duran® maintained its hardness and elastic modulus more consistently. The elastic modulus of Duran® was higher in both pre- and post-thermocycling tests. Thermocycling reduced Erkodur® hardness but had no impact on elastic modulus. These findings suggest material properties may influence clinical outcomes. The study does not propose new materials but highlights differences in current options. The results may guide clinicians in material selection for aligner fabrication. The authors emphasize the importance of considering mechanical stability in orthodontic practice.