The purpose of the study was the evaluation of the bond strength of a provisional resin to a polyetheretherketon (PEEK) using different surface treatments and conditioning methods.
PEEK disks were polished with 600 grit rotating silicon carbide papers. Plexiglas tubes were filled and bonded with a provisional resin (Luxatemp Fluorescence) to the PEEK disks which were air-abraded either with 110 μm alumina particles (Rocatec Pre) and conditioned with the primers Ecusit Composite Repair, Luxatemp Glaze & Bond or Clearfil Ceramic Primer or they were tribochemically silica-coated (Rocatec Plus) and silanated with Espe Sil or Clearfil Ceramic Primer. Air-abraded PEEK disks without priming served as control. Subgroups of 8 specimens each were stored in distilled water at 37 °C either for 3 days without thermal cycling (TC) or for 150 days with additional 37,500 thermal cycles between 5 and 55 °C (dwell time 30 s). Following storage tensile bond strength (TBS) was tested at a crosshead speed of 2 mm/min in a universal testing machine. Statistical analysis was conducted with Kruskal–Wallis test followed by Wilcoxon rank sum test adjusted by Bonferroni–Holm.
After 3 days TBS ranged from 0 to 15.0 MPa. After artificial aging over 150 days TBS ranged from 0 to 12.9 MPa. Using air-abrasion and priming with Luxatemp Glaze & Bond resulted in significantly higher TBS than all other methods, which was also durable over time.
The use of the methylmethacrylate containing primer Luxatemp Glaze & Bond after air-abrasion of PEEK surfaces can be recommended clinically as promising bonding method to PEEK.
PEEK (polyetheretherketone) is a semicrystalline thermoplastic with good mechanical properties , high melting point (about 335 °C), easy processing, high stiffness, good dimensional stability at high temperature and is chemically stable to nearly all organic and inorganic chemicals. Additionally, PEEK shows resistance to radiation damage and compatibility with many reinforcing agents like glass or carbon fibers. All these characteristics make it highly attractive in industrial applications and is also considered an advanced biomaterial used in medical implants, often reinforced by biocompatible fibers such as carbon .
In dentistry, PEEK is currently used for the fabrication or clasps and removable dental prostheses and as material for provisional implant abutments . Especially for the latter application a clinically adequate bonding to PEEK is required when the abutments are to be modified with provisional resins to create an optimal emergence profile and soft tissue support .
In a recent study no adhesion to air-abraded or silica-coated PEEK was achieved when a universal composite luting resin (RelyX Unicem) was used . However the application of an unfilled resin (Heliobond) and a fine hybrid composite resin (Tetric) resulted in reasonable initial bond strengths of 11.5–13.5 MPa. Additional acid etching with sulfuric acid resulted in increased initial bond strengths up to 21.4 MPa . However using sulfuric acid etching for chair-side PEEK abutment modification seems hazardous and should rather be avoided. In addition, no artificial aging was used in both available studies on bonding dental resins to PEEK . So it is still unknown whether bonding to PEEK withstands the hydrolytic effects due to water uptake which often reduced resin bonding to oxide ceramics dramatically . However adequate bonding durability would a prerequisite for intraoral usage of bonded peek restorations.
Therefore, the purpose of the current study was to evaluate chairside available surface conditioning methods and adhesion promoters regarding their ability to promote adhesion to PEEK. In addition the bonding durability was tested using long-term water storage and thermal cycling. The null hypothesis tested was that there is no influence of the surface bonding method on resin-PEEK bonding and its durability.
Materials and methods
Ninety-six PEEK disks with a diameter of 8 mm and a thickness of 4 mm were cuts out of PEEK rods (Kern GmbH, Technische Kunststoffteile, Großmaischeid, Germany). The bonding surfaces of all specimens were polished with 600 grit rotating silicon carbide paper under water rinsing. The materials utilized and their characteristics are listed in Table 1 .
|Component||Batch no.||Main composition a||Manufacturer|
|Clearfil Ceramic Primer||004EA||3-Methacryloxypropyl-trimethoxysilane, 10-methacryloyloxydecyl-dihydrogenphosphate, ethanol||Kuraray, Osaka, Japan|
|Ecusit Composite Repair||621546||Aliphatic, aromatic dimethacrylate, carboxylic methacrylate||DMG, Hamburg, Germany|
|Espe Sil||357609||3-Methacryloxypropyl-trimethoxysilane, ethanol||3M Espe, Seefeld, Germany|
|Luxatemp Glaze & Bond||608356||Multifunctional acrylates, methyl methacrylates, catalysts, stabilizers, additives||DMG, Hamburg Germany|
|Luxatemp Fluorescence||591872||Glass powder, silicium dioxide, urethandimethacrylate, aromatic dimethacrylate, glycolmethacrylate||DMG, Hamburg, Germany|
All PEEK disks were ultrasonically cleaned in 99% isopropanol for 3 min and then dried with air for 15 s prior to bonding. Specimens were classified into the following six experimental groups consisting of 16 specimens each according to differences in surface conditioning and applied adhesion promotor.
|Pre-NO||Air-abrasion with Rocatec Pre at 0.28 MPa for 15 s and cleaned with compressed air for 15 s. Then bonding with Luxatemp Fluorescence without any adhesion promotor.|
|Pre-Ecu||Air-abrasion with Rocatec Pre at 0.28 MPa for 15 s and cleaned with compressed air for 15 s. Then application of Ecusit Composite Repair with a residence time of 5 min in the dark and bonding with Luxatemp Fluorescence.|
|Pre-CCP||Air-abrasion with Rocatec Pre at 2.8 MPa for 15 s and cleaned with compressed air for 15 s. Then application of Clearfil Ceramic Primer with a residence time of 180 s and bonding with Luxatemp Fluorescence.|
|Pre-LGB||Air-abrasion with Rocatec Pre at 0.28 MPa for 15 s and cleaned with compressed air for 15 s. Then application of Glaze & Bond with a residence time of 5 min in the dark and bonding with Luxatemp Fluorescence.|
|Plu-SIL||Air-abrasion with Rocatec Pre at 0.28 MPa for 15 s followed by Rocatec Plus at 0.28 MPa for 15 s and cleaned with compressed air for 15 s. Then application of Espe Sil with a drying time of 5 min and bonding with Luxatemp Fluorescence.|
|Plu-CCP||Air-abrasion with Rocatec Pre at 0.28 MPa for 15 s followed by Rocatec Plus at 0.28 MPa for 15 s and cleaned with compressed air for 15 s. Then application of Clearfil Ceramic Primer with a residence time of 180 s and bonding with Luxatemp Fluorescence.|
Tensile bond strength testing
Plexiglas tubes with an inner diameter of 3.2 mm were filled with a self-curing composite provisional resin (Luxatemp Fluorescence). Seven minutes after filling the tubes they were bonded with the same resin (Luxatemp Fluorescence) to the conditioned PEEK surfaces by means of an alignment apparatus. This resin which contains no adhesive monomers was chosen because it is widely used as provisional resin to modify the shape of implant abutments and to fabricate provisional crowns and fixed dental prostheses . The alignment apparatus consisted of two parallel guides, a tube holder, a silicon pad and an added weight of 750 g. The apparatus ensured that the tube axis was perpendicular to the bonding surface. The bonding procedure in detail has been described in previous studies . Excess cement was removed from the bonding margin using small disposable brushes.
Each bonding group was divided into two subgroups of 8 specimens each and stored in distilled water at 37 °C either for 3 days without thermal cycling (TC) or for 150 days with additional 37,500 thermal cycles between 5 and 55 °C (dwell time 30 s). Following the different storage time, tensile bond strength (TBS) was tested at a crosshead speed of 2 mm/min in a universal testing machine (Zwick Z010/TN2A; Ulm, Germany) using a special test configuration, which provided a moment-free axial force application. A collet held the tube while an alignment jig allowed self-centering of the specimen. The jig was attached to the load cell and crosshead by upper and lower chains, allowing the whole system to be self-aligning.
The fractured interfaces of the PEEK specimens were examined with a light microscope (Wild Makroskop M 420; Heerbrugg, Germany) at 30× magnification to calculate the debonded area which was assigned to adhesive or cohesive failure modes. After sputtering using a gold-alloy conductive layer of approximately 15 nm, representative specimens were examined using a scanning electron microscop (SEM; XL 30 CP; Eindhoven, Netherlands) with an acceleration voltage of 15 keV and a working distance of 10 mm .
Statistical analysis was performed using the Wilcoxon rank sum test. Significance levels were adjusted with Bonferroni–Holm correction for multiple testing.