Effects of surface treatments on the adhesion strengths between polyether ether ketone and both composite resins and poly(methyl methacrylate)

Abstract

Background: This study evaluated the effects of three surface treatments-concentrated H₂SO₄, sodium borohydride (NaBH₄), and their combination-on the shear bond strengths between polyether ether ketone (PEEK) and both composite resins and poly(methyl methacrylate) (PMMA).

Methods: 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.

Results: 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.

Conclusion: 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.

Keywords: Composite resin; Poly(methyl methacrylate); Polyether ether ketone; SOdium Borohydride; Shear bond strength; Sulfonation.

Fig. 1

Schematic diagram of this study

Fig. 2

Shear Bond Strength Bonding Specimen Preparation Process. a Specimen placed on the central bottom of the mold; b Pouring superhard gypsum; c PTFE bonding mold; d Bonding resin rod to the PEEK specimen surface; e Finished bonding specimen; f Shear bond strength testing of the bonding specimen

Fig. 3

Bonding specimen failure mode diagram

Fig. 4

SEM images of PEEK specimens after surface treatment by five methods (a) SEM of P-PEEK, b SEM of D-PEEK, c SEM of B-PEEK, d SEM of S-PEEK, e SEM of SB-PEEK

Fig. 5

Cross-sectional SEM images of PEEK specimens after surface treatment by five methods (a) cross-sectional SEM of P-PEEK, b cross-sectional SEM of D-PEEK, c cross-sectional SEM of B-PEEK, d cross-sectional SEM of S-PEEK, e cross-sectional SEM of SB-PEEK

Fig. 6

XPS spectra of PEEK specimens after surface treatments (a-e) represent the C1 spectra of P-PEEK, D-PEEK, B-PEEK, S-PEEK, and SB-PEEK, f-j represent the O1 spectra of the same specimens

Fig. 7

ATR-FTIR spectra of PEEK specimens treated with a silane coupling agent (a) P-PEEK ATR-FTIR, b D-PEEK ATR-FTIR, c B-PEEK ATR-FTIR, d S-PEEK ATR-FTIR, e SB-PEEK ATR-FTIR

Fig. 8

Three-point bending test results of PEEK specimens treated by five methods

Fig. 9

Shear bond strength between PEEK and composite resin, and PEEK and PMMA (a) Shear bond strength between PEEK and composite resin; b Shear bond strength between PEEK and PMMA

Fig. 10

Shear bond strength between PEEK and composite resin, and PEEK and PMMA after aging (a) Shear bond strength between PEEK and composite resin; b Shear bond strength between PEEK and PMMA

Fig. 11

Distribution of shear bond strength failure modes between PEEK and composite resin, and PEEK and PMMA (a) Shear bond strength failure mode distribution between PEEK and composite resin; b Shear bond strength failure mode distribution between PEEK and PMMA)

Fig. 12

CCK-8 cytotoxicity results for PEEK specimens treated by five methods after 1 day, 4 days, and 7 days

Fig. 13

DAPI staining results for PEEK specimens treated by five methods

Fig. 14

Schematic of silane coupling between PEEK and both composite resins and PMMA