Abstract

Evaluating the shear bond strength (SBS) of contemporary universal adhesive systems on different substrates is critical for understanding their clinical applicability. In this study, the SBS of universal adhesives was assessed on 144 human and bovine tooth specimens, comparing enamel and dentin across etch-and-rinse and self-etch protocols. Following single-step or two-step adhesive application and resin cementation, the specimens were subjected to 5000 thermocycles before being evaluated with a universal testing machine. Failure modes and surface morphology were additionally characterized using stereomicroscopy and scanning electron microscopy (SEM). Statistical analyses revealed that both tissue type (p = 0.043) and tooth type (p < 0.001) significantly influenced SBS, while the main effect of the adhesive protocol was not significant (p = 0.485). A significant interaction occurred between tissue type and adhesive protocol (p = 0.013); Post hoc analyses revealed that Group A enamel had significantly higher bond strength than both Group D enamel (p = 0.026) and Group A dentin (p = 0.001). Observed failures were predominantly adhesive or mixed, and SEM confirmed expected acid-induced surface roughness. Human teeth yielded higher bond strengths than bovine teeth, meaning absolute SBS values from bovine lab studies should be used with caution.

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