Deproteinization with Papain enzyme improves the bonding performance of self-etch adhesives to eroded dentin

To evaluate the effect of papain enzyme pretreatment on the bonding performance of self-etch adhesives (SEAs) to eroded dentin, assess its proteinizing effect, and examine the ultrastructure of the pretreated eroded dentin surface and resin-dentin interface. Artificially eroded dentin surfaces were created and pretreated with papain enzyme, while untreated eroded dentin surface served as a control. The treated dentin surfaces were bonded with Clearfil SE Bond 2 (SEB) and Clearfil Universal Bond Quick (UBQ). Microtensile bond strength (µTBS) was measured after 24-hour storage and after 10,000 thermocycles, between 5 °C and 55 °C. Additionally, the deproteinizing effect was evaluated by comparing changes in the amide-to-phosphate ratio using Raman microscopy. Dentin morphology and resin-dentin interface were investigated using scanning electron microscopy. Statistical analysis was performed using three-way ANOVA with Tukey's post hoc tests, and t-tests (p < 0.05). Pretreatment with papain enzyme slightly increased the initial µTBS of SEB, while significantly increasing the initial µTBS of UBQ (p < 0.05). Furthermore, papain enzyme could stabilize the µTBS of both adhesives after thermocycles (p > 0.05). It also significantly reduced the amide-to-phosphate ratio (p < 0.05) altered the surface morphology and improved the structure of resin-eroded dentin interfaces. Deproteinization with papain enzyme dissolved the organic components on the eroded dentin surface, leading to the improvement of resin infiltration, increased thickness of the hybrid layer, and improved the bond durability of SEAs to eroded dentin. The application of the papain enzyme as a pretreatment has the potential to enhance and maintain the bonding performance of self-etch adhesives to eroded dentin. This leads to improved adhesion and restoration quality on compromised eroded dentin surfaces.