Comparative Antibacterial Efficacy of Orthodontic Brackets Coated with Titanium Dioxide, Copper Oxide, and Hydroxyapatite-Silver Nanoparticles Against Streptococcus mutans

Background: The development of dental caries around orthodontic brackets is a common complication of orthodontic treatment. Objectives: This study aimed to compare the antibacterial efficacy of stainless steel (SS) brackets coated with copper oxide nanopar- ticles (CuO-NPs), titanium dioxide nanoparticles (TiO2-NPs), and hydroxyapatite silver nanoparticles (HA-SNPs) against Streptococcus mutans. Methods: In this in vitro, experimental study, 20 orthodontic brackets were assigned to four groups (n = 5, each group). One group served as the no-intervention control group, and the brackets in the remaining three groups underwent dip coating with CuO-NPs, TiO2-NPs, and HA-SNPs < 100 nm. The number of S. mutans colonies was counted after 24 h, one week, and one and three months. Data were analyzed using the Shapiro Wilk test, repeated measures ANOVA, and Bonferroni multiple comparisons test. Results: All three experimental groups exhibited similar antibacterial properties after 90 days of trial (P > 0.05). Moreover, CuO-NPs had a greater inhibitory effect than TiO2-NPs on S. mutans after 24 h (P = 0.007). However, the inhibitory effect of HA-SNPs was not significantly different from that of TiO2-NPs (P = 0.259) or CuO-NPs (P = 0.224). Conclusions: Considering the similar antibacterial properties of all three coatings in the long term, all three types of nanoparticles can be used to coat orthodontic brackets to prevent caries. However, due to the high cost and difficult preparation of HA-SNPs and the slightly higher efficacy of CuO-NPs in the short-term, the latter may be preferred for this purpose.