Evaluation of micro tensile bond strength of newly introduced universal adhesives using different bonding strategies and lining technique on human dentin: In-vitro study

Aim: This study evaluated the immediate and aged micro-tensile bond strength (µTBS) of two universal adhesives: OptiBond eXTRa™ (Kerr) and BeautiBond Xtream™ (Shofu). It also investigated the impact of applying a flowable composite over the adhesive before placing the composite resin restoration, and analyzed fracture modes and the resin/dentin interface via SEM. Materials and methods: Eighty human molars were randomly assigned to eight groups based on adhesive type, bonding strategy (Etch-and-Rinse [E&R] vs. Self-Etch [SE]), whether a flowable composite was used, and aging periods (24 hours and 6 months). The bonding procedures involved specific etching, adhesive application, and curing protocols, followed by micro-tensile testing at a rate of 1 mm/min. Results: Indicated significant interactions between the adhesive type and bonding strategy, as well as between bonding strategy and aging time. After 24 hours, no significant difference in µTBS was observed between E&R and SE. However, the application of a flowable composite significantly enhanced bond strength in the Kerr adhesive compared to Shofu. Notably, bond strength diminished significantly after six months. Conclusion: the two-step universal adhesive demonstrated superior bond strength and durability due to better hybrid layer formation, while the E&R strategy proved more effective than SE. Incorporating a flowable composite lining enhanced bonding effectiveness for both adhesive types, regardless of the bonding mode employed.