An in-vitro investigation of the bond strength of experimental ion-releasing dental adhesives to caries-affected dentine after 1 year of water storage

Abstract

Objective: The aim of this study was to evaluate the bonding performance after 1 year storage of an experimental dental adhesive containing analogues of phosphoproteins and fluoride-doped bioglass (EXP), applied in self-etching (SE) or etch & rinse (ER) mode, to caries-affected dentine after selective caries removal.

Materials and methods: Fifty human molars with dentine carious lesions were excavated selectively using Carisolv^TM gel and then connected to simulated pulpal pressure system. Teeth were divided randomly into five groups based on the tested materials: EXP-SE, EXP-ER, a resin-modified glass-ionomer cement (RMGIC), a three-step adhesive system (OPT) and a universal adhesive applied in SE mode (UA-SE). The specimens were submitted to different analytical tests (μTBS, SEM fractographic analysis and dye-enhanced confocal microscopy) at baseline (T0) and after 1 year (T1).

Results: At T0 there was no difference in bond strength between the tested materials (p>0.05). At T1, EXP-SE and EXP-ER were the only materials to show no significant reduction in bond strength (p<0.05). The SEM showed a clear presence of minerals deposited on the dentine surface after bonding in the EXP-SE and EXP-ER groups. The specimens restored with RMGIC showed no exposure of the dentine surface after failure. The OPT and UA-SE specimens showed clear signs of degradation at the interface. Confocal microscopy imaged mineral precipitation at the interface of the EXP groups.

Conclusion: Conventional adhesives may have inadequate bonding performance with evident degradation at the dentine-bonded interface over time. Although the RMGIC may present a drop in bond strength after prolonged storage, the bonding interface may result less affected by degradation over time. Innovative ion-releasing adhesives may remineralise the caries-affected dentine and achieve a stable bond over time.

Clinical significance: GIC-based materials may represent an appropriate dentine replacement material after selective chemo-mechanical caries removal rather than conventional adhesive systems.

Keywords: Bioglass; Caries-affected dentine; Interface degradation; Ion-releasing adhesives; Phosphoproteins; Selective caries removal.