EXPERIMENTAL DETERMINATION OF THE MECHANICAL PROPERTIES OF MATERIALS USED FOR THE FABRICATION OF ORTHODONTIC ALIGNERS

Relevance. The clinical effectiveness of orthodontic aligners is largely determined by the mechanical properties of the polymer material, which influence aligner stiffness, deformation behavior, and the magnitude of forces transmitted to the teeth. The use of averaged material properties in finite element modeling may reduce the accuracy of calculations, since commercially available polymers differ in their composition, layered structure, and thermomechanical behavior. Objective. To determine and compare the mechanical properties of materials used for the fabrication of orthodontic aligners and to establish an experimental database for subsequent finite element analysis. Materials and Methods. A comparative study was performed on 60 specimens of six materials: Ustom, Avantis, Aligners, 3A Medes, single-layer StarSmile, and three-layer StarSmile, with 10 specimens in each group. Following vacuum thermoforming, uniaxial tensile testing was carried out using a universal testing machine at a crosshead speed of 2 mm/min and a preload of approximately 10 N. Local strains were assessed using digital image correlation, with data processed in Ncorr software. Statistical analysis included one-way analysis of variance, Levene’s test, and the Games–Howell post hoc test. Results. The highest Young’s modulus and ultimate tensile strength were recorded for Ustom, at 1,177.73 MPa and 35.98 MPa, respectively. The lowest Young’s modulus was observed for three-layer StarSmile at 261.87 MPa. This material also demonstrated the highest strain at ultimate tensile strength, reaching 10.72 %. The lowest strength values were recorded for three-layer StarSmile and Avantis. Material type had a statistically significant effect on both Young’s modulus and ultimate tensile strength (p < 0.001). Conclusion. Material composition and multilayer structure substantially influence the mechanical response of orthodontic aligner materials. The obtained values should be used as material-specific input parameters when developing a finite element model of the “aligner–tooth–periodontal ligament–alveolar bone” system.