Bond Strength, Microleakage, Microgaps, and Marginal Adaptation of Self-adhesive Resin Composites to Tooth Substrates with and without Preconditioning with Universal Adhesives

Purpose: This study investigated and compared the bond strengths, microleakage, microgaps, and marginal adaptation of self-adhesive resin composites (SAC) to dentin with or without universal adhesives.
Materials and Methods: Dentin surfaces of 75 molars were prepared for shear and microtensile bond strength testing (SBS and µTBS). Silicon molds were used to build up direct restorations using the following materials to form 5 groups: 1. Surefil One; 2. Prime&Bond active Universal Adhesive + Surefil One; 3. Vertise Flow; 4. OptiBond Universal + Vertise Flow; 5. Scotchbond Universal + Filtek Z500 (control group). Bonded specimens were thermocycled 10,000x before being tested either for SBS or µTBS using a universal testing machine at a crosshead speed of 0.5 mm/min. Direct mesial and distal class-II cavities were created on 100 sound premolars, with the gingival margin of distal cavities placed below CEJ and restored according to the five groups. After thermocycling, microleakage scores were assessed following immersion of restored premolars in 2% methylene blue dye for 24 h, while marginal gaps and adaptation percentages were investigated on epoxy resin replicas under SEM at magnifications of 2000X and 200X, respectively. Results were statistically analyzed with parametric and non-parametric tests as applicable, with a level of significance set at α = 0.05.
Results: Bond strengths, microleakage scores, microgaps, and percent marginal adaptation of Surefil One and Vertise Flow were significantly (p < 0.001) inferior to the control group. Dentin preconditioning with universal adhesives significantly increased the study parameter outcomes of Surefil One and Vertise Flow, yet they were still significantly below the performance of the control group.
Conclusion: Conventional resin composite outperformed the SAC whether applied solely or in conjunction with their corresponding universal adhesives.