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Introduction

High-performance polymers (HPPs) [ , ] are semi-crystalline thermoplastic materials consisting of aromatic benzene molecules connected by functional ether or ketone groups, resulting in different combinations of polyaryletherketones [ , ]. Polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) are commonly used HPPs, especially in dental applications [ ]. There is great interest and ongoing research in tissue-substitute materials that have human bone-like mechanical characteristics. In this context, HPPs may help meet patient demands for metal-free dental reconstructions owing to their biocompatibility and their mechanical properties of heat resistance, solvent resistance, excellent electrical insulation, and robust wear and fatigue resistances [ , ]. In addition, the natural radiolucency of HPPs makes prostheses made of them amenable to diagnostic imaging, such as computed tomography, magnetic resonance imaging, and X-ray, with less artifact interference than metal-based restorations [ ]. These properties make HPPs an attractive alternative to ceramic and metal for restorations.

HPPs are used for many dental applications, including transitional and healing abutments [ ], dental implants [ ], dental clasps [ ], and as alternative rigid materials for removable partial denture prosthesis frameworks [ ] and fixed dental prostheses [ ]. HPP devices can be formed in thermo-pressing procedures (e.g. BioHPP®, Bredent, and Senden products) or milled with computer-aided design/manufacturing techniques (e.g. Juvora Dental Disc® products) [ ].

Because of the low translucency and greyish or pearl-white opaque color of HPPs, these materials are not suitable for monolithic esthetic dental restorations, [ ] requiring a resin-composite surface veneer to achieve satisfactory aesthetics [ ]. Furthermore, their chemical inertness, low surface energy, and resistance to surface modification has made it difficult to bond materials to HPP materials, which may explain, at least part, why HPPs are not yet commonly used in restorative and prosthetic dentistry [ , ]. HPP surface property modification has become a research hotspot with the goal of increasing HPP surface free energy and thus HPP bonding performance [ , , , ].

There are two highly regarded surface treatment classes: mechanical and chemical. Mechanical treatments include airborne-particle (silica or aluminum oxide) abrasion, laser and plasma applications, and bur grinding. Chemical treatments include etching with sulfuric acid and Piranha solution as well as the application of adhesive primers, such as Visio.link® (Bredent, Senden, GE) and Signum PEEK Bond® (Heraeus Kulzer, Hanau, GE) [ , , ]. Surface treatments, especially chemical etching and mechanical roughness induction, are thought to improve material adhesiveness by diversifying functional groups [ ]. Sulfuric acid has been shown to increase surface porosity and permeability, thereby facilitating mechanical bonding without resin tag formation [ ]. Conversely, plasma treatment increases material wettability, thereby increasing the bond strength potential of HPPs with resin materials [ ].

Knowledge concerning the potential and limitations of each treatment, with its particular specific effects, is limited and a standard protocol for enhancing HPP dental prostheses is lacking. From a clinical perspective, the use of caustic solutions (e.g. sulfuric acid or piranha solution) for chair-side HPP frameworks and abutments would be hazardous and should be avoided or restricted. The purpose of this study was to investigate the impact of different surface conditioning methods and adhesion promoters on the strength of veneering composite resin bonding to common HPPs, namely PEEK and PEKK. Secondarily, postconditioning bonding durability was analyzed. We tested the null hypothesis that resin-HPP bonding and durability are not affected by PEEK/PEKK prebonding treatments.

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Materials and methods