Clinical performance of a bulk-fill versus a nanofilled resin composite in non-carious cervical lesions with different extensions: a 6-years randomized, parallel, double-blind clinical trial

Objectives To evaluate the clinical performance of a regular bulk-fill (Filtek Bulk Fill Posterior) and a regular nanofilled (Filtek Z350 XT) resin composite in restoring non-carious cervical lesions (NCCLs) with different occlusogingival distance (OGD). Methods A randomized, parallel, double-blind controlled trial was conducted with 77 participants. One hundred and forty NCCLs were categorized by their OGD as 1.5 mm (±10%) or 3 mm (±10%). Lesions were randomized into four groups (n=35) and restored with Filtek Bulk Fill Posterior (1.5 mm-B and 3 mm-B) or Filtek Z350 XT (1.5 mm-C and 3 mm-C). The self-etch adhesive Clearfil SE Bond was used in all procedures. Two calibrated, blinded examiners evaluated the restorations at 6 years (range 66-94 months) using modified USPHS criteria. Survival analysis (retention/fracture) was performed using Kaplan-Meier (Log-rank test), and secondary outcomes were analyzed with Friedman’s and Wilcoxon tests (α=0.05). Results After 6 years, 99 restorations were evaluated. Thirteen restorations were lost resulting in retention rates of 85.7% for 1.5 mm-C, 91.4% for 1.5 mm-B, 91.4% for 3 mm-C, and 91.4% for 3 mm-B. Significant marginal discrepancy was observed for 1.5 mm-B, 3 mm-C, and 3 mm-B (p < 0.01). Fifty-eight restorations showed minor marginal staining and 72 were rated Bravo for surface texture, with no significant differences among groups or compared to the 30-month evaluation (p>0.05). No significant difference was found for the other parameters. Conclusion The regular bulk-fill demonstrated similar clinical performance to the regular nanofilled resin composite in NCCLs, regardless of the OGD after 6 years of clinical service. Clinical significance This is the first 6 years clinical trial showing the long-term behavior of a bulk-fill resin composite in NCCLs. The OGD of NCCLs appears not to influence the clinical performance of resin composite.