**5. Conclusions**

This study explored the potential of incorporating unique imidazolium-based polymerizable antibacterial monomers into orthodontic bonding cements. For unfilled resins comprising up to 12 wt % ABR-C, no significant decreases in flexural strength or modulus were observed. For experimental cements incorporating 1–4 wt % ABR-C, there is no drastic compromise to the SBS to enamel except for 3 wt % ABR-C; moreover, their SBS values are all comparable to those of the commercially available orthodontic cements. The ISO-22196 antimicrobial test against *S. aureus* showed significant levels of antibacterial e ffects—up to over 5 logs of microorganism reduction exhibited by ABR-C-containing experimental cements. Although MIC and MBC were identified, and a range of antibacterial activities of imidazolium-based orthodontic cements were demonstrated, clinical and long-term studies are still important to validate the e fficacy of this unique series of imidazolium resins towards preventing and mitigating WSLs for patients.

**Author Contributions:** H.L. and X.J. contributed equally to conceptualization; methodology; validation; formal analysis; investigation; resources; data curation; writing—original draft preparation; writing—review and editing; visualization; supervision; and project administration. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** We would like to thank Anuradha Prakki and her team at University of Toronto for assistance with the MIC and MAC tests. We would also like to thank David Pashley and his team at Augusta University for the dentin mass loss and HYP content study. We also greatly appreciate the laboratory assistance provided by Donna Reid and Brandon Zhang.

**Conflicts of Interest:** The authors declare no conflict of interest.
