This in vitro study compared the shear bond strength (SBS) and antibacterial efficacy of an orthodontic adhesive containing either cinnamon or titanium dioxide (TiO₂) nanoparticles (NPs). A total sample of 120 freshly extracted teeth was randomly divided into three groups, according to the type of NPs incorporated into adhesive for metallic orthodontic brackets’ bonding: group 1—conventional orthodontic adhesive (TXT) as a control; group 2—conventional orthodontic adhesive mixed with TiO₂ NPs (TXT + TNP); and group 3—conventional orthodontic adhesive mixed with cinnamon NPs (TXT + CNP). The SBS and adhesive remnant index (ARI) scores were evaluated and compared between the groups. The antibacterial efficacy against Streptococcus mutans for all the groups was assessed via a disc agar diffusion test. Data comparisons among groups were performed by ANOVA followed by Bonferroni post hoc test. Antibacterial efficacy comparison between the experimental groups was performed via an independent t-test. The significance level for all the tests was set at p ≤ 0.05. The highest mean SBS values (10.11 ± 1.88 MPa) were in the TXT control group followed by TXT + TNP (9.40 ± 1.78 MPa), and the lowest SBS was in the TXT + CNP (8.99 ± 1.77 MPa) group. The mean SBS among the experimental groups was non-significant (p = 0.241). Antibacterial effects significantly increased (p ≤ 0.05) in both experimental groups. However, TXT + TNP revealed a significantly higher antibacterial effect (p = 0.021) than TXT + CNP. In conclusion, incorporating cinnamon or TiO₂ NPs into an orthodontic adhesive improves its antibacterial effects without compromising the bond strength for clinical purposes.