The effect of different surface treatments on the bond strength of PEEK composite materials
Introduction
Polyetheretherketone (PEEK) is one of the most popular high-performance engineering plastics currently available. PEEK is highly advantageous for applications in many industries, including aerospace, automotive, electronics, and medical equipment, because of its attractive mechanical properties, such as heat resistance, solvent resistance, excellent electrical insulation, good wear resistance, and high fatigue resistance [1], [2], [3]. Several in vivo and vitro studies have shown the good biocompatibility of PEEK [4], [5]. Some studies have designed PEEK composites with porous scaffold structures and mixed them with bioactive materials to improve the biological activity of PEEK [6], [7], [8]. The material also has good dimensional stability; its elastic modulus is between those of cortical and cancellous bone [9]. In addition, PEEK is naturally radiolucent and compatible to imaging techniques, such as computed tomography (CT), magnetic resonance imaging (MRI), and X-ray. The radiolucency of PEEK allows the examination, diagnosis, and treatment of clinical diseases without need for substructure removal or replacement. Thus, PEEK can replace traditional materials (such as titanium and stainless steel) in metallic orthopedic, spinal, and trauma implants [3], [10], [11].
Modification techniques, such as blending, filling, and fiber reinforcement, are necessary for the design of new PEEK-based materials with optimum properties needed in various application fields [12], [13], [14], [15]. Polyetherimide (PEI)/Nano-SiO2/PEEK ternary composite materials showed superior mechanical properties and proper biocompatibility in comparison to pure PEEK. The tensile strength, flexural strength and other mechanical properties of the composites were at optimum levels when the content of nano-SiO2 was set to 7%.
In dentistry, PEEK is mainly applied in transitional abutments [16], healing caps [17], and orthodontic bite sticks. Some excellent physical and biological properties of PEEK meet basic prosthetic requirements in clinical practice. But, the grayish and opaque color of PEEK limits the application in full-coverage restorations. Therefore, PEEK needs to combine with composite resin or veneering. However, the bond strength of the material is low when combined with composite resin because of the inert chemical performance, low surface energy, and surface modification resistance of PEEK [18]. Thus, improving the surface properties of PEEK has become a research hotspot. Adhesive properties, which are important for the stability of prosthesis in dental applications, are influenced by the surface treatment and luting cement. In present study, the commonly used dual cure resin cement (RelyX™ Unicem) and the dentin adhesive (SE Bond) were chosen. Resin cements have become the most commonly used adhesive in the dental field. The adhesive can provide higher retention, better edge seal, and more durable bond effect than conventional luting cements [19]. The resin cement can penetrate into the porous surface of the adherend to form a resin nail, causing obvious effects on micro-mechanical retention. SE Bond is a two-steps sixth generation self-etching dentin adhesive system that can effectively penetrate into the dentin surface with exposed collagen fibers to form a resin protrusion and maintain a closed-state adhesive surface for good bonding effect.
Therefore, this study aims to provide effective treatment methods and suitable adhesives for PEEK composite materials in dental applications by evaluating the ability of currently available surface conditioning methods and luting cements to establish adhesion to PEEK composite materials. It was hypothesized that the different surface treatment methods may affect the bond strength of PEEK composite materials, irrespective whether a universal composite resin cement (RelyX™ Unicem) or an adhesive/composite resin (SE Bond/Clearfil AP-X™) was used.
Section snippets
Materials and methods
Two light-curing adhesive systems, RelyX™ Unicem (3M Co. Espe, Germany) or SE Bond (Kuraray, Japan) and Clearfil AP-X™ (Kuraray, Japan), were selected for this study. The descriptions of the adhesives and the resin material included in this study are summarized in Table 1.
Results
The surfaces after the different pretreatments are shown by scanning electron microscopy (SEM). SEM analysis showed that the polished PEEK composite materials (Group A) produced slight surface scratches, although the structure was regular (Fig. 1). Sulfuric acid etching resulted in a porous and blister-like dissolution of the PEEK material (Fig. 2). Hydrofluoric acid etching had a slight effect on topography. Abrasive tracts created by grinding were still evident on the surfaces, but the traces
Discussion
PEEK is an ideal dental restoration material owing to its good biocompatibility and excellent mechanical properties. In a recent study, the PEEK three-unit FDPs showed a visible deformation of 1200 N, which was higher than the mastication forces of up to 600 N in the posterior region. PEEK has been demonstrated to be suitable for fixed dental prostheses (FDPs), especially in load-bearing areas [20]. PEEK composite material of this study reinforced with 7 wt% Nano-SiO2 greatly improves the
Conclusions
Within the limitations of this study, it can be concluded that 98% sulfuric acid and argon plasma treatments improved the bond strength of PEEK composites with resin cement RelyX™ Unicem or the two-steps self-etching adhesive SE BOND. Therefore, the null hypothesis was accepted. Comparing the pooled data of the two cements, SE Bond/Clearfil AP-X™ seemed suitable to bond to PEEK composite materials. However, the use of 98% sulfuric acid is not clinically viable for the corrosive performance.
Acknowledgements
This research was supported by the Natural Science Foundation of Jilin (No. 201215051) and Jilin Provincial Industrial Technology Research and Development Project (No. JF 2012C009-2) from China.
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