**5. Conclusions**

The present study incorporated a not ye<sup>t</sup> investigated quaternary ammonium MYTAB into a dental resin, which achieved potent antibacterial e ffects against dental plaque microcosm biofilms for the first time. The results showed that (1) MYTAB at 2% greatly decreased *S. mutans* in planktonic and biofilm stages compared to GCtrl, (2) higher MYTAB mass fraction rendered the adhesive more strongly antibacterial, (3) MYTAB at 1% mass fraction greatly reduced the cell viability, and (4) the incorporation of MYTAB at a maximum concentration of 2% had no detrimental e ffect on the degree of conversion and ultimate tensile strength. MYTAB-containing dental resin is a promising strategy for dental applications.

**Author Contributions:** P.A.M.S. contributed to design, data acquisition, and analysis, and drafted the manuscript; I.M.G. contributed to design, data acquisition, and analysis, and drafted the manuscript; J.N. contributed to data acquisition and analysis; F.V. contributed to data acquisition and analysis; V.C.B.L. contributed to design, data analysis, and data interpretation; M.A.M. contributed to data analysis and data interpretation, and drafted the manuscript; F.M.C. contributed to conception, design, data acquisition, analysis, and interpretation, and drafted and critically revised the manuscript. All authors have read and agreed to the published version of the manuscript.

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

**Acknowledgments:** This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001.

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