Effect of esterase aging on the micro-shear bond strength of amide-modified and conventional universal adhesives to dentin (in vitro study)

Background: The degradation of the resin--dentin interface remains a major limitation of adhesive restorations. Esterase-mediated hydrolysis of adhesive polymers may accelerate bond deterioration and contribute to interfacial failure. Objectives: This study aimed to compare the micro-shear bond strength (μSBS) of two universal adhesives, Clearfil Universal Bond Quick and All-Bond Universal, after aging in porcine liver esterase by using self-etch and etch-and-rinse strategies. Materials and Methods: Eighty sound human mandibular third molars provided 160 standardised dentin blocks. Each adhesive was applied in self-etch or etch-and-rinse mode, composite cylinder of 1 mm in diameter applied. Then, the resin--dentin samples were stored in phosphate-buffered saline (PBS) or porcine liver esterase (6 U/mL) for 4 weeks at 37 °C, with medium renewal every 48 h (n = 20/group). μSBS was measured at 0.5 mm/min. Resin biodegradation was assessed by high-performance liquid chromatography of bis-hydroxy-propoxy-phenylpropane (BisHPPP) release, and failure modes were evaluated stereomicroscopically. Results: Esterase aging significantly reduced μSBS for both adhesives in both modes (p < 0.001). In self-etch mode, μSBS decreased from 32.20 ± 8.02 MPa to 14.45 ± 3.66 MPa for All-Bond Universal and from 36.75 ± 7.60 MPa to 21.25 ± 6.71 MPa for Clearfil Universal Bond Quick. In etch-and-rinse mode, the μSBS values decreased from 35.75 MPa ± 10.03 to 16.50 ± 5.67 MPa and from 41.10 ± 9.08 MPa to 24.25 ± 5.58 MPa, respectively. Under enzyme aging, Clearfil Universal Bond Quick showed significantly higher μSBS than All-Bond Universal in both modes (p < 0.001). BisHPPP release was markedly higher in enzyme groups than PBS controls, and enzyme-aged specimens failed mainly adhesively. Conclusions: Esterase aging significantly weakened resin--dentin bonding and increased resin biodegradation. The amide-modified Clearfil Universal Bond Quick showed better bond strength retention than All-Bond Universal under enzymatic challenge.