The objective of this study is to determine the effect of aging on tensile strength and surface condition of orthodontic aligners on days 0, 1, 5, 7, 10, and 14. The total sample of 80 aligners included five brands (Accusmile^®, Angel^®, GRAPHY^®, Invisalign^® and Suresmile^®) were placed in a thermocycler to imitate the temperature variations of the oral cavity and accelerate aging for 50, 250, 350, 500, and 700 cycles. The mechanical tensile properties (Young’s modulus E, yield strength YS, maximum elastic stress MES, Ultimate Tensile Strength UTS, and maximum stress MS) were measured by Universal Testing Machine at a rate of 5 mm of deformation per minute for 4 minutes. Microscopic observations were made under a voltage of 10 kV at magnifications times 50, 250, 500, 1000, and 2500 after cleaning with ethanol and ultrasound then metallization with gold. YS and MES of Angel^® aligners are statistically reduced after five days of aging (P = .003). Aligners from the most rigid to the most flexible are (decreasing E): Accusmile^® > GRAPHY^® > Suresmile^® > Invisalign^® > Angel^®. Surface conditions also deteriorated with aging (appearance of scratches, porosity, cracks, etc.). GRAPHY^® aligners are more heterogeneous and weaker than others. In vitro study Mechanical properties of Accusmile^®, GRAPHY^®, Invisalign^®, and Suresmile^® were not affected by aging. YS and MES were reduced from day 5 for Angel^® aligners. Surface conditions are also altered by aging.

The purpose of the study is to compare the hardness of different metallic brackets to enamel and to determine their chemical composition and microstructure. Five metallic brackets (0.022″ × 0.028″ inch) from seven orthodontic firms produced in different alloys (Discovery^® Smart/Empower^®/Genius^®2 Metal/Victory^TM series/Equilibrium^®/Damon Q) were chosen (n = 35). The hardness of the brackets and enamel was measured using a microhardness tester. The study of the chemical composition of brackets was carried out on a single bracket per series. A scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS) detector was used. Analysis of the chemical composition of metallic brackets was obtained with Oxford Instruments Ultim Max Aztec software. Metallic brackets’ hardness varied from 203 to 439 HV. A significant difference exists between Ti Equilibrium^® brackets, the rest of the brackets and the enamel (p-value = 0.003). No significant difference was found between SS_a(stainless-steel alloy), Co-Cr_a(Cobalt-Chrome) brackets and the enamel. The chemical study confirms that the alloys used to produce metallic brackets validate all the data of the manufacturers except for Genius^®2 Metal; according to this study, they are considered to be Co-Cr_a alloys. The study of the composition of brackets made it possible to confirm manufacturers’ data. Genius^®2 Metal brackets, Empower^®2 and Victory^TM series brackets filled the properties needed for orthodontic treatment. The hardness of metallic brackets is influenced by the alloy used and manufacturing method. Co-Cr_a brackets with hardness comparable to enamel can be considered as an alternative to SS_a brackets in patients allergic to nickel.

Objectives: The aim of this study was to compare the hardness, chemical composition, and microstructure of various self-ligating ceramic orthodontic brackets and enamel. Methods: Sixty ceramic brackets (0.022″ × 0.028″) from six different orthodontic firms (Damon^® Clear 2, Genius^® Crystal, Empower^® 2 Clear, Clarity^® Ultra, Alpine SL^® Clear, and Experience Ceramic^®) were tested using a microhardness tester and a scanning electron microscope (SEM) equipped with energy-dispersive spectroscopy (EDS). Results: The hardness of the ceramic brackets ranged from 1969.8 to 2567.3 VH. The statistical analysis using the Kruskal–Wallis and Mann–Whitney tests revealed significant differences in microhardness between most of the ceramic brackets. Additionally, this study found that passive self-ligating brackets exhibited a significantly higher hardness than that of active self-ligating brackets (p = 0.01). The SEM analysis showed that the variations in the oxygen and alumina composition between the six bracket types were also statistically significant (p = 0.01). Conclusions: Among all of the ceramic brackets tested, Alpine^® brackets displayed the lowest hardness values, making them a potential choice for minimizing enamel damage. Notably, the hardness of self-ligating ceramic brackets was found to be at least six times greater than that of enamel, raising concerns about their potential to cause trauma to the enamel of antagonistic teeth. Consequently, the researchers recommend avoiding bonding ceramic brackets to the mandibular teeth or elevating occlusion with turbo-bites to prevent traumatic contact during treatment.