Effect of Dentin Deproteinization Using Sodium Hypochlorite and Bromelain Enzyme on Microtensile Bond Strength of Self-etch Adhesive at Different Dentin Depths: An in-Vitro Study

Background Dentin bonding remains a clinical challenge in daily dental practice especially bonding to deep dentin due to structural differences compared to superficial dentin. The study aimed to evaluate the effect of dentin deproteinization using sodium hypochlorite (NaOCl) and bromelain enzyme on the microtensile bond strength (µTBS) and failure modes of one-step self-etch adhesive system to superficial and deep dentin. Methods Forty-eight sound human third molars were randomly assigned into two main groups according to dentin depth (superficial and deep). Each group was further subdivided into three subgroups (n = 8) according to surface treatment: control (no pretreatment), 10% NaOCl, and 10% bromelain enzyme. After adhesive application and resin composite buildup, specimens were thermoscycled then sectioned into beams to be subjected to µTBS testing. Failure modes were analyzed under stereomicroscopy. Data was analyzed and the significance level was set at (p ≤ 0.05). Results In superficial dentin, the control group showed significantly higher µTBS values (26.78 ± 6.11 MPa) compared with NaOCl (20.55 ± 4.82 MPa) and bromelain (19.55 ± 4.22 MPa), with no significant difference between the two deproteinizing agents. In deep dentin, both NaOCl (23.02 ± 5.35 MPa) and bromelain (20.86 ± 3.61 MPa) significantly improved µTBS compared with control (16.06 ± 3.61 MPa), with NaOCl showed higher mean values compared to bromelain. Failure mode analysis revealed more adhesive failures in deproteinized superficial dentin, while deep dentin treated with NaOCl showed predominating cohesive failures within resin composite. Conclusions Deproteinization with sodium hypochlorite or bromelain enhances bonding to deep dentin but jeopardizes bonding to superficial dentin