Impact of Biomimetic Primer on Bonding of Ion-Releasing Adhesives

Objective This study evaluated the dentine bonding performance of an experimental adhesive containing fluoride-doped calcium phosphate (FDCP) at baseline (T0) and after thermocycling (TC). Additionally, it assessed fractographic and resin-dentine interface ultramorphology, as well as the effect of the tested materials on dentine enzymatic activity. Methods The experimental system consisted of an ion-releasing flowable composite (VS10-R20%) and a universal adhesive (AD/VS10-R10%; pH 3.1), applied on acid-etched dentine with or without a biomimetic dual-analogue primer (pH 7.0). A commercial universal adhesive (SCH: Scotchbond Universal) and a glass ionomer cement (GIC: RIVA SC) were controls. Specimens underwent microtensile bond strength (µTBS) testing after 24 hours or TC (10,000 cycles). Failure mode and fractographic SEM analyses followed µTBS testing. Confocal microscopy assessed interfacial nanoleakage at T0 and after TC. Enzymatic activity was evaluated through in-situ and gelatine zymography on dentine powder pretreated with the materials. Results SCH control obtains a significant µTBS reduction after TC, mostly adhesive failures, and collagen degradation. Furthermore, strong enzymatic activity, especially post-TC, was observed. GIC control also registered a lowest µTBS values but stable after TC and, despite gaps and nanoleakage post-TC, enzymatic activity remained consistent with T0. Finally, experimental system obtains lower µTBS than SCH but stable after TC. SEM revealed minimal exposed collagen fibrils, mineral deposition, and reduced enzymatic activity compared to controls. A reflective layer beneath the hybrid layer and limited dye penetration indicated improved bonding interface integrity. Conclusions The FDCP-based experimental bonding system showed stable dentine bonding after aging. Its ion-releasing ability, especially with the biomimetic primer, effectively preserved the hybrid layer and reduced enzymatic degradation, suggesting its potential for durable adhesive restorations.