Comparison of the physical-mechanical properties and resistance to colouration of different clear aligner materials

Aim: The aim of this study was to determine the physical-mechanical changes and color changes caused by different liquid exposure in aligners produced by direct (Clear A, Graphy Tc-85) and indirect (CA Pro, Invisalign) methods. Methods: Clear aligner samples from different brands were evaluated with three different tests. Samples of two different sizes were prepared for the cyclic loading test and tensile test. The coloration test samples were the right central incisors in the maxillary aligners produced for the cyclic loading test. Two types of samples produced for the cyclic loading test and tensile test were kept in seven different liquids (distilled water, orange juice, soy sauce, cola, red wine, tea and coffee) in an oven at 37 °C for 24 hours. In the coloration test, the samples were kept in the same seven liquids at 37 °C for 24 hours, 3 days and 7 days. The cyclic loading test was carried out by applying forces on the samples in 1, 5, 10, 50 repetitions to reach a deformation depth of 1 mm, in a mechanism that can exhibit precise movements in all three axes of space. The tensile test was performed with an Esetron microtensile device, which has two independent tips moving away from each other at a speed of 5 mm/min to determine the elastic modulus, tensile strength and elongation at break values. Coloration test measurements of the samples were made using a colorimeter device (LS173 D/8). Results: In the cyclic load test, the aligner group in which the increasing number of repetitions caused the least difference in mechanical properties was Graphy Tc-85. Among the tensile tested samples, CA Pro samples exhibited the lowest modulus of elasticity and tensile strength, while their elongation at break values were the highest. In the coloration test, samples immersed in soy sauce showed the largest ΔE value for all four aligner groups. Conclusion: No harmonious relationship has been determined between the amount of change in the mechanical properties of liquids with different pH values as a result of exposure to clear aligners and the pH values of the liquids. In the experimental groups of all four clear aligners, the tensile strength and modulus of elasticity decreased significantly, while the elongation at break increased compared to the control groups. When each of seven different liquids was compared between groups, Invisalign samples showed the highest ΔE values in each liquid.