Purpose: The aim of this study was to evaluate the clinical success potential of two nanocomposites placed in posterior teeth using an antibacterial adhesive system over 18 months. Methods: A total of 49 Class I and 47 Class II restorations were placed in the permanent teeth of thirty adult patients. The carious lesions were restored with Grandio (Voco) or Filtek Supreme (3M ESPE) using a two-step self-etching antibacterial adhesive system Clearfil Protect Bond (Kuraray). The restorations were finished with fine-grit diamond burs, Enhance polishing system, and Sof-Lex finishing brushes. The restorations were evaluated at baseline, 6, 12, and 18 months after placement using modified Ryge criteria for color stability, marginal discoloration, marginal adaptation, caries formation, anatomic form, postoperative sensitivity, surface roughness, and retention. Results: The changes in the parameters were assessed using the Cochran Q test and the McNemar test at a significance level of p 0.05. All restorations were classified as clinically satisfactory after 18 months. Statistical analysis demonstrated differences only in superficial roughness, with Grandio exhibiting more surface roughness than Filtek Supreme (p 0.05). Conclusion: Posterior restorations built up with the novel nanocomposites using an antibacterial self-etching system showed satisfactory results at the 18-month recall appointment relative to all criteria except the surface texture in the case of Grandio. Further evaluations are necessary for a more in-depth analysis. Keywords: nanofill, nanohybrid, antibacterial adhesive, posterior restorations