Clinical evaluation of different bi-layer biomimetic strategies of composite resin in large class I cavities: an 18-month randomized clinical trial

OBJECTIVE: The aim of this study was to conduct a randomized, double-blind, split-mouth comparative clinical trial to clinically assess and compare different bi-layer biomimetic strategies of composite resin in large class I cavities over an 18-month period. MATERIALS & METHODS: A total of 160 posterior composite restorations in 40 participants of age 35-45 years old were enrolled in the study based on inclusion criteria. Each patient received four different bilayer biomimetic bases in four equal groups (n = 40) as follows: Group I: short-fiber reinforced composite (everX Posterior, GC Corporation, Tokyo, Japan); Group II: long-fiber reinforced composite (polyethylene fibers, Ribbond Inc., USA); Group III: Resin-Modified Glass Ionomer Cement (RMGIC) (Riva SDI, Bayswater, VIC, Australia); and Group IV: flowable composite (G-aenial universal Flo, GC Corp., Tokyo, Japan). A 2 mm surface layer of nanohybrid composite resin (Tetric Evo Ceram, Ivoclar Vivadent) was applied to cover the biomimetic base in all groups. Occlusal Class I cavities were prepared according to caries extension with a cavity depth of 4-5 mm. No bevels were prepared. Clinical assessment was carried out according to the World Dental Federation (FDI) by two calibrated evaluators at baseline and at 6, 12, and 18 months for aesthetic properties (surface and marginal staining), functional properties (fracture and retention, marginal adaptation), and biological properties (postoperative sensitivity, secondary caries). Statistical analysis employed Friedman and Kruskal-Wallis tests. The level of significance was established at α = 0.05 across all tests. RESULTS: Forty patients with a total of 160 restorations were evaluated in line with FDI at the end of the study with 100% recall rates. No fracture or secondary caries was reported over an 18-month evaluation period. The intragroup (Friedman test) and intergroup (Kruskal-Wallis test) comparisons revealed no statistically significant differences among short fiber reinforced composite, long fiber reinforced composite, resin-modified glass ionomer cement, and flowable composite for the assessed criteria over time (p > 0.05). CONCLUSION: All tested bilayer biomimetic composite resins have comparable excellent short-term clinical performance by the end of the study period. TRIAL REGISTRATION: The protocol of the current study was approved by the Research Ethics Committee of the Faculty of Dentistry, Tanta University, Egypt, with approval number #R-RD-03-25-3194. This study was registered at www. CLINICALTRIALS: gov with the identification number NCT07285772 on 15/12/2025-'retrospectively registered.'