**5. Conclusions**

CeO2 was investigated for the first time as a promising filler to improve the radiopacity of dental adhesives. The particles were chemically analyzed and then used in experimental adhesives formulation. Through of incorporation of CeO2 particles at 1.44 vol.%, the dental adhesives were able to show increased radiopacity and a proper degree of conversion. The restorative materials here proposed could be a reliable strategy to assist clinicians diagnose recurrent caries.

**Author Contributions:** I.M.G., contributed to data analysis, data interpretation, and drafted the manuscript; V.C.B.L., contributed to design, data acquisition, data analysis, and data interpretation; A.S.T., contributed to data analysis and data interpretation; C.P.B., contributed to data analysis and data interpretation; S.M.W.S., contributed to design and data interpretation; M.A.M., contributed to data interpretation, drafted the manuscript, and critically revised the manuscript; F.M.C., contributed to conception, design, data acquisition, analysis, and interpretation, and drafted and critically revised the manuscript. All authors gave final approval and agreed to be accountable for all aspects of the work.

**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 (scholarship).

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