The aim of this systemic review, conducted in accordance with the PRISMA statement, was to investigate the impact of surface pretreatments on the bonding strength of high performance polymers (HPPs).
Eight databases were searched through March 2019. Risk of bias was assessed and random effects meta-analyses were applied to analyze mean differences in shear bond strength (SBS) and tensile bond strength (TBS), considering surface pretreatments and bonding agents after 24h and thermocycling.
A total of 235 relevant titles and abstracts were found, yielding 11 final selections. Low risk of bias was observed in most studies. For polyetheretherketone (PEEK) specimens, random-effect models showed that, compared to non-treated controls, pretreatments associated with Visio.link® (Bredent, Senden, GE) increased TBS by 26.72 MPa (95% confidence interval (CI), 19.69–33.76; p < 0.00001) and increased SBS by 4.86 MPa (95% CI, 2.61–7.10; p < 0.00001). Air abrasion improved SBS by 4.90 MPa (95% CI, 3.90–5.90; p < 0.00001) (50 μm alumina) and 4.51 MPa (95% CI, 1.85–7.18; p = 0.0009) (silica-coated CoJet). In comparison to non-treated controls, Visio.link® and Signum PEEK Bond® (Heraeus Kulzer, Hanau, GE) increased SBS by 33.76 MPa (95% CI, 18.72–48.81; p < 0.00001) and 33.28 MPa (95% CI, 17.48–49.07; p < 0.00001), respectively. No differences were found between Visio.link® and Signum PEEK Bond® or Monobond Plus/Heliobond® (Ivoclar Vivadent, Schaan, LH) (p > 0.05). Similar results were observed for polyetherketoneketone (PEKK) specimens.
This review shows improved HPP bonding following the application of various surface pretreatments, including air abrasion and bonding agents.
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.
Materials and methods
This systematic review was structured in accordance with PRISMA (Preferred Reporting Items for Systematic Review and Meta Analyses Protocols) [ ] and the PRISMA checklist [ ]. The PICOS framework applied was: P opulation, HPP specimens; I ntervention, surface pretreatment and bonding agent application; C omparison, untreated specimens; O utcomes, tensile bond strength (TBS) and shear bond strength (SBS); and S tudy design, in vitro studies. The addressed focused question was: “Does surface pretreatments and/or bonding agent application impact the bond strength between composite veneering resin and HPP?”
Studies evaluating the ability of surface treatments to improve HPP bonding strength for dental applications were included to this review. No publication time or language restrictions were applied. There were five exclusion criteria for collated studies: a) HPP was not used for a dental purpose; b) surface treatments were not applied or compared; c) no analysis of a control group [untreated specimens or omission of bonding agent recommended by the manufacturer (Visio.link® or Signum PEEK Bond®)]; d) bonding strength not measured or results not presented in MPa; e) <5 specimens per subgroup; f) publication type is review, letter, abstract, opinion, case report/series, or book chapter.
Information sources and search strategy
The search was elaborated using combinations of terms that were adapted for each of the following electronic databases: Embase, Latin American and Caribbean Health Sciences, PubMed, SCOPUS, and Web of Science. In addition, a grey literature search was conducted on Google Scholar, Open Grey, and ProQuest. The searches were conducted from database inception through the search performance date, which was September 17, 2018. An update was performed in March 15, 2019 (Supplementary Table 1).
Following the recommendation by Greenhalgh and Peacock [ ], reference lists of included studies were hand-searched to find additional potentially relevant references. Reference management and removal of duplicates were performed in EndNote X8 software (Thomson Reuters, Philadelphia, USA).
Studies were selected in two phases. In phase one, two reviewers (authors L. T. G. and T. M. D.) screened titles and abstracts independently to identify eligible studies. In phase two, collated studies identified as potentially eligible were subjected to a full-text reading. Doubt or discrepancies were solved by consensus and discussion with the third reviewer (A. G. P.). In both phases, a team of three experts (M. O., A. G. P., and L. A. M. M.) crosschecked all of the information. If any disagreement remained regarding eligibility, it was discussed between the research team and the coordinator (T. M. S. V. G.).
Data extracted from included papers were registered independently by two researchers (L. T. G. and T. M. D.), tabulating data of interest in an Excel spreadsheet (Microsoft Corporation, Redmond, USA). HPP specimen characteristics, the number of specimens examined, the veneering composite(s) applied, surface roughness, type of bonding strength test applied (TBS or SBS), type of surface pretreatment, and main conclusions described in the papers were recorded ( Table 1 ).
|Study||Specimens (brand/dimensions)||N total (N/ each group)||Veneering composite||Negative control (pretreatment)||Pretreatments||Positive control (adhesives)||Experimental adhesive system||Main Conclusions|
|Ates et al. 2018||PEEK BreCAM.BioHPP,
10 × 15 × 2.5mm
|540 (90)||Crea.lign opaker A2, Crea.lign and Crea.lign paste A2 (Bredent)||No pretreatment||G1 : Air abrasion (50 μm alumina poder; 15 s, 2.7 atm); G2 : Air abrasion (silica-coated – Cojet system;15s, 2.7 atm); G3 : Laser (Er:YAG laser, 2.940 nm, 150 mJ, 10 Hz, 1.5 W); G4 : Laser (Er:YAG laser, 2.940 nm, 150 mJ, 10 Hz, 1.5 W) + Air abrasion (50 μm alumina powder 15 s, 2.7 atm); G5 : Laser (Er:YAG laser, 2.940nm, 150 mJ, 10 Hz, 1.5W) + Air abrasion (silica-coated – Cojet system;15 s, 2.7 atm)||Group A : Visio.link, Bredent;||None||Air abrasion with Aluminum oxide and silica coating, combined or not to Er:YAG laser, improve bonding of veneering materials to PEEK frameworks|
|Bötel et al. 2018||PEEK Juvora Dental; DC 4420, Evonik; DC4450, Evonik;
10 × 15 × 2.5 mm
|272||VITA VM LC (Vita Zahnfabrik); GC Gradia (GC Europe); c) GC Gradia Direct Flo (GC Europe)||No pretreatment||G1: Air abrasion (100 μm alumina powder (Control); G2 : Air abrasion (100 μm alumina powder) + Plasma (Oxygen for 3 min); G3 : Air abrasion (100 μm alumina powder + Plasma (Oxygen for 35 min); G4 : Air abrasion (100 μm alumina powder) + Plasma (Argon/Oxygen for 3 min); G5 : Air abrasion (100 μm alumina powder) + Plasma (Argon/Oxygen for 35 min);||Group A : Visio.link, Bredent;||None||The surface pretreatment of diverse PEEK types with low-pressure plasma, prior to veneering with composite, has a positive impact on the adhesive bonding between PEEK and composites. In addition, the light-bodied composite Gradia Direct Flo achieved the highest SBS.|
|Çulhaoglu et al. 2017||PEEK BreCAM.BioHPP, 10 mm diameter × 4 mm||198 (11)||Combo.lign (Bredent)||No pretreatment||G1 : Air Abrasion (silica-coated – Cojet system – 3 bars); G2 : Acetone Treatment 99% (60 s); G3 : Sulfuric Acid 98% (60s); G4 : Air Abrasion (100 μm alumina powder – 2bars); G5: Laser (Yb:PL laser, 5 W, 250 ms)||Group A : Visio.link, Bredent;||None||Highest mean shear bond strengths were observed for acid-etched PEEK surfaces followed by laser-irradiated, airborne particle abraded, and silica coated surfaces.|
|Fokas et al. 2019||PEKK PEKKTON, 8mm diameter ×3 mm||250 (5)||Nexco, Ivoclar Vivadent||No pretreatment||G1: Air abrasion with 110 μm alumina powder – Rocatec Pre (2 bars); G2: Sulfuric Acid 98% (60 s); G3: Air abrasion with 110 μm silica-coated alumina – Rocatec Plus (2bars); G4: Sulfuric Acid 98% (60 s) + Air abrasion with 110 μm silica-coated alumina||Grupo A: Visio.link, Bredent;||Grupo B: Monobond-S, Ivoclar Vivadent||Air-abrasion with Rocatec Plus on polished or sulfuric-etched PEKK surface can significantly increase the tensile bonding stability as well as durability of resin composite to PEKK.|
|Keul et al. 2014||PEEK Dentokeep, 7 mm × 7 mm × 2 mm||640(16)||Signum Composite Dentin A3 (Heraus Kulzer); Signum Ceramics Dentin A3 (Heraus Kulzer)||No pretreatment||G1 : Air Abrasion (50 μm alumina powder); G2 : Piranha Solution (30 s); G3 : Air Abrasion (50 μm alumina poder) + Piranha Solution (30 s);||Group A : Visio.link, Bredent;||Group B : Monobond Plus/Heliobond (Ivoclar Vivadent); Group C : Clearfil Ceramic Primer (Kuraray Noritake Dental); Group D : Signum PEEK Bond I + II (Heraeus Kulzer)||Air abrasion, combined or not to piranha solution, followed by adhesive agents (Visio.link, Signum PEEK Bond, or Monobond Plus/Heliobond) seemed to generate reliable bond strengths for the veneering of PEEK with resin composites.|
|Lee et al. 2014||PEKK Pekkton Ivory, 7 mm × 7 mm × 2 mm||150 (10)||Filtek Z350 XT (3M ESPE)||N/D||G1 : Sulfuric Acid 95% (60s); G2 : Air Abrasion (50 μm alumina powder; 0.5MPa, 20 s); G3 : Air Abrasion (110 μm silica-coated; 0.5 MPa, 20 s);||Group A : Visio.link, Bredent;||Group B : Luxatemp Glaze & Bond (DMG); Group C : Single Bond Universal (3M ESPE); Group D : All-Bond Universal (Bisco), Group E: Monobond Plus + Heliobond (Ivoclar Vivadent)||The combination of air-abrasion with MDP or MMA-containing bond materials are recommended. Single Bond Universal can be an effective bonding material to PEKK.|
|Schwitalla et al. 2017||PEEK Juvora Dental; DC 4420, Evonik; DC4450, Evonik; 10 x 15 x 2.5 mm||120 (10)||VITA VM LC (Vita Zahnfabrik)||No pretreatment||G1 : Plasma (Argon + Oxygen, 35 min, 0.3 mbar, 100 kHz, 200 w); G2 : Air Abrasion (100 μm alumina powder; G3 : Air Abrasion (100 μm alumina + Plasma (Argon + Oxygen, 35 min, 0.3 mbar, 100 kHz, 200 w);||Group A : Visio.link, Bredent;||None||Air abrasion and surface activation with low-pressure argon/oxygen plasma, in combination with an adhesive agent, increases shear bond strength, especially in unfilled PEEK material.|
|Stawarczyk et al. 2013||PEEK Dentokeep, 7 mm × 7 mm × 2 mm||576 (16)||Sinfony (3M ESPE); GC Gradia (GC Europe); VITA VM LC (VITA Zahnfabrik)||No pretreatment||G1: Air Abrasion (50μm alumina powder)||Group A : Visio.link, Bredent;||Grupo B : Z-Prime Plus (BISCO), Group C : Ambarino P60 (Creamed), Group D : Monobond Plus (Ivoclar Vivadent); Group E : Signum PEEK Bond I+II (Heraeus Kulzer)||Pre-treatment with Monobond Plus increased the TBS values. The highest TBS before and after thermocycling between PEEK and all tested veneering resins was observed for groups pre-treated with Visio.link and Signum PEEK Bond.|
|Stawarczyk et al. 2014||PEEK Dentokeep, 7 mm × 7 mm × 2 mm||720 (20)||Sinfony (3M ESPE); VITA VM LC (VITA Zahnfabrik)||No pretreatment||G1: Sulfuric Acid (98%); G2: Piranha Solution;||Group A : Visio.link, Bredent;||Grupo B: Signum PEEK Bond I+II (Heraeus Kulzer)||Adhesive systems should be applied to ensure a durable bond. Acid pretreatment of PEEK surface is not required. The veneering resin composites show no effect on the results.|
|Stawarczyk et al. 2017||PEKK Pekkton Ivory, 10 mm × 10 mm × 4 mm||1200 (20)||Anaxblend Opaquer Paste (Anaxdent); Anaxblend Dentin Flow (Anaxdent); Anaxblend Dentin Paste (Anaxdent)||No pretreatment||G1 : Air abrasion (100 μm alumina powder); G2 : Air Abrasion (100 μm alumina powder) + Plasma (Oxygen, 15 s, 20 W);||Group A : Visio.link, Bredent;||Group B: PEKK Bond (Anaxdent)||Oxygen plasma treatment, in combination with adhesives increases TBS. Visio.link showed higher TBS to PEKK than did PEKK Bond. Flowable veneering composite also increased TBS in comparison to packable veneering composite.|
|Stawarczyk et al. 2018||PEEK – Tizian PEEK, 10 × 10 × 3 mm||400 (20)||Dialog Occlusal (Schütz Dental)||N/D||G1 : Air Abrasion (50 μm alumina powder; 0.05 MPa); G2 : Air Abrasion (50 μm alumina powder; 0.35 MPa); G3 : Air Abrasion (100 μm alumina poder; 0.05 MPa); G4 : Air Abrasion (100 μm alumina poder; 0.35 MPa); G5 : Air Abrasion (100 μm silica-coated – Rocatec; 0.35 MPa);||Group A : Visio.link, Bredent;||Group B : Scotchbond Universal (3M ESPE); Group C : Monobond Plus + Heliobond (Ivoclar Vivadent); Group D: Dialog Bonding Fluid (Schütz Dental).||PEEK conditioning with Visio.link increased TBS values with the smallest number of prefailured specimens compared to the remaining adhesive systems. The grain size of the air-abrasion powder particle did not show an effect on the TBS.|