The Microhardness and Chemical Composition of Different Ceramic Self-Ligating Brackets: An In Vitro Study

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.