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

Orthodontic clear aligners as an alternative to traditional braces have become increasingly ubiquitous in the last few years. Therefore, understanding the properties of the aligner materials can help to produce more accurate results of the treatment and provide more data for orthodontists who are currently using or intend to use this technology. This study aimed to investigate the effect of thermocycling on some mechanical properties (Hardness and Elastic Modulus) of two thermoplastic products used in the fabrication of orthodontic aligners. Two thermoplastic products of Duran® 0.75 mm and Erkodur® 1 mm were used in this study. A specially prepared disk fabricated from risen material with dimensions of (15mm) in diameter and (6mm) in thickness which was fabricated with a 3D printer was used for hardness assessment. Twenty sheets were thermoformed over the round disk for each product. Whereas, for elastic modulus, a Dog bone specimen with dimensions 8 mm in width and 150 mm in length was made from resin by using a 3D printer. The shore D hardness test was used to measure the hardness of the two products before and after thermocycling. For elastic modulus, thermoplastic sheets that were less than 1mm in thickness were measured according to the ASTMD 882-02 and those with 1mm were measured according to the ASTMD 638-02a. The elastic modulus was measured using a tensile test by a universal testing machine before and after thermocycling. Erkodur model® was higher than Duran® in the hardness test before and after thermocycling. But, Erkodur model® showed significant, however, Duran® showed no significant change in hardness before and after thermocycling. The elastic modulus test for the two materials showed a significant difference between Duran® and Erkodur® models. The elastic modulus of Duran® was higher than Erkodur® before and after thermocycling. The hardness of the Erkodur® product was higher than that of Duran®, whereas the elastic modulus of the Duran® product was higher than Erkodur® before and after thermocycling. On the other hand, thermocycling reduces the hardness of the Erkodur® product more than that of Duran® and did not affect the elastic modulus of each product.