PEEK specimens (n = 160) were randomly assigned to composite resin and PMMA groups, each of which was subdivided into normal and aging groups (n = 40), each comprising samples that were pristine (untreated) or treated with dimethyl sulfoxide (DMSO), NaBH4, or concentrated H2SO4 or sequentially treated with NaBH4 and concentrated H2SO4 (n = 8). The shear bond strength (SBS) of the normal and aged specimens were measured. For the normal and treated specimens, the surface and cross-sectional morphologies were analyzed using scanning electron microscopy (SEM), the chemical bond modifications were investigated using X-ray photoelectron and attenuated total reflectance Fourier-transform infrared spectroscopies (XPS and ATR-FTIR, respectively), the mechanical strengths were measured using three-point bending tests, and the cytotoxicities were evaluated using cell-counting kit-8 (CCK-8) assays and 4′,6-diamidino-2-phenylindole (DAPI) staining.
NaBH4 etched the PEEK surface, generating a fibrous texture, while concentrated H2SO4 produced a surface possessing variously sized pores. Sequential treatment with NaBH4 and concentrated H2SO4 produced dense, permeating pores. XPS confirmed that NaBH4 reduced carbonyl groups to hydroxyl groups on the PEEK surface. ATR-FTIR spectroscopy confirmed that the silane coupling agent grafted onto the PEEK surface, forming Si–O–C bonds. NaBH4 and concentrated H2SO4 both strengthened the shear bonding between the PEEK and both the composite resins and PMMA (P < 0.05). The specimens sequentially treated with NaBH4 and 98% concentrated H2SO4 possessed the strongest shear bonding (P < 0.05). The aged specimens sequentially treated with NaBH4 and concentrated H2SO4 retained very strong shear bonds. CCK-8 cytotoxicity assays and DAPI staining confirmed that these surface treatments meet oral biocompatibility standards.
NaBH4 introduced chemical bonds to the PEEK surface, while concentrated-H2SO4-induced sulfonation enhanced the micromechanical interlocking between the PEEK and both the composite resins and PMMA. These combined physicochemical modifications significantly strengthened the adhesion between the PEEK and both the composite resins and PMMA and effectively strengthened PEEK’s bonding.