Radiographic appearance of proximal resin composite restorations bonded with a radiopaque or radiolucent universal adhesive: a randomized clinical trial

Objectives This trial evaluated the radiographic appearance of resin composite restorations bonded with a radiopaque universal adhesive compared with a radiolucent universal adhesive, assessed by digital radiography based on modified USPHS criteria. Materials and methods Seventy-four participants with class II cavities were randomly assigned to two groups ( n = 37). The intervention group received radiopaque universal adhesive (Scotchbond Universal Plus, 3M ESPE, St. Paul, USA), while the control group received radiolucent universal adhesive (Single Bond Universal adhesive, 3M ESPE, St. Paul, USA). Selective enamel etching was performed, followed by adhesive application and restoration with nanofilled resin composite (Filtek Z350XT, 3M ESPE, St. Paul, USA). Postoperative periapical radiographs were used to evaluate the appearance of the tooth-restoration interface according to modified USPHS criteria, classifying restorations as Alpha (absence of radiolucent line) or Bravo (presence of radiolucent line). Categorical data were analyzed using Fisher’s exact test. Absolute risk reduction (risk difference) with 95% confidence interval was calculated to estimate the difference in the risk of detecting a radiolucent adhesive line between the two groups. Results A statistically significant difference was observed between the two groups ( P = 0.025). Restorations bonded with the radiopaque adhesive demonstrated a 16.2% absolute reduction in the risk of exhibiting a radiolucent line at the tooth-restoration interface compared with those bonded using the radiolucent adhesive (95% CI: 3.71–28.73%). Conclusions The radiopaque universal adhesive resulted in significantly fewer restorations with visible radiolucent lines at the tooth-restoration interface immediately after restoration placement and may facilitate radiographic interpretation of proximal resin composite restorations. Trial Registration https://clinicaltrials.gov/ , (NCT05907928).