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Published on: December 20, 2024
Mechanical properties of thermoplastic and 3-dimensional printed thermoset orthodontic aligner materials: An in vitro
Bethany Cook1, Nicholas Shirey1, Christian Groth1
1From the Department of Orthodontics and Pediatric Dentistry, School of Dentistry, The University of Michigan, Ann Arbor, Mich.
Introduction:
Shape-memory polymers (SMPs) have been proposed for use in the direct printing of clear aligners. The purpose of this study is to evaluate and compare the mechanical properties of SMPs and thermoplastic materials.
Methods:
Samples of SMPs, Tera Harz Direct Aligner Clear (TC-85, Graphy Inc, Seoul, South Korea) and Dental Clear Aligner (DCA, LuxCreo Inc, Chicago, Ill), and a thermoplastic material, polyethylene terephthalate glycol (PET-G, Dentsply Sirona, Charlotte, NC), were fabricated, wet-conditioned, and tested for yield strength, ultimate tensile strength (UTS), stress and strain at failure, as well as stress relaxation and modulus relaxation. The SMPs underwent stress relaxation testing twice, with the second run (Run 2) conducted after shape recovery. Statistical analysis included 1-way analysis of variance followed by Tukey post-hoc analysis and independent t tests to determine significance (P <0.05).
Results:
PET-G exhibited the highest values for yield strength, UTS, strength at failure, and strain at failure, followed by DCA, and TC-85 had the lowest strength values (P <0.001). For stress relaxation, PET-G had the lowest values of stress loss and modulus loss (P <0.001), with a total stress loss of 23% and modulus loss of 38%. The stress loss of DCA and TC-85 was 83%-99%, and the modulus loss was 89%-99%. Both TC-85 and DCA had greater total stress and modulus loss at Run 2 than at Run 1.
Conclusions:
There were significant differences in yield strength, UTS, and strength at failure, stress relaxation, and modulus relaxation for the materials. There was also a significant decrease in stress relaxation and modulus relaxation for SMP materials between Run 1 and Run 2.
