Abstract
Objectives
To assess the bonding potential of a universal composite resin cement and an adhesive/composite system to differently pre-treated PEEK surfaces.
Methods
One hundred and fifty PEEK disks were embedded in epoxy resin, polished (P4000 grit) and treated as follows ( n = 30/group): (A) no treatment, (B) acid etching with sulfuric acid (98%) for 1 min, (C) sandblasting for 10 s with 50 μm alumina, (D) sandblasting for 10 s with 110 μm alumina and (E) silica coating using the Rocatec system (3M ESPE). Polished and sandblasted (50 μm alumina) cp titanium (grade 4) served as a control. Acrylic hollow cylinders were either luted with a universal composite resin cement (RelyX Unicem) or an unfilled resin (Heliobond) and a hybrid composite (Tetric) to the specimens. Bond strength was measured in a shear test and failure modes were assessed. Statistic analysis was performed with one-way ANOVA followed by a post hoc Scheffé test and unpaired t -tests.
Results
With the universal composite resin cement, no bond could be established on any PEEK surfaces, except specimens etched with sulfuric acid (19.0 ± 3.4 MPa). Shear bond strength to titanium was significantly lower (8.7 ± 2.8 MPa, p < 0.05). Applying the adhesive/composite system, shear bond strength values on pre-treated PEEK ranged from 11.5 ± 3.2 MPa (silica coating) to 18.2 ± 5.4 MPa (acid etched) with no statistically significant differences ( p > 0.05). No bond was obtained on the polished surface.
Significance
Bonding to PEEK is possible when using a bonding system. No adherence can be achieved with the tested universal composite resin cement except on an etched surface. The results strongly encourage further research in PEEK application in dentistry.
1
Introduction
PEEK (polyetheretherketone), also referred to as polyketones, is obtained from aromatic dihalides and bisphenolate salts by nucleophilic substitution. The bisphenolate salt is formed in situ from bisphenol and either added sodium or added alkali metal carbonate or hydroxide, by the Williamson ether synthesis. PEEK is a semicrystalline thermoplastic with good mechanical properties . The chemical structure of polyaromatic ketones provides stability at high temperatures (exceeding 300 °C), resistance to chemical and radiation damage, compatibility with many reinforcing agents (such as glass and carbon fibers), and greater strength (on a per mass basis) than many metals, making it highly attractive in industrial applications, such as aircraft and turbine blades, for example . PEEK is also considered an advanced biomaterial used in medical implants, often reinforced by biocompatible fibers such as carbon . In dentistry, this material is mainly used as a plastic temporary abutment for implants in the fabrication of temporary crowns . The material is biocompatible and features a natural tooth-color appearance. In addition, PEEK can easily be shaped with dental burs. In the field of restorative and prosthetic dentistry, PEEK has not found much attention yet, basically due to difficulties in establishing a strong and durable adhesion to composite resin materials owing to its low surface energy and resistance to surface modification by chemical treatments . Until now, industry bonds elastomers to PEEK typically by conventional abrasive treatments, acid etching, laser treatment or plasma techniques to prepare the engineering plastic’s surface followed by the application of epoxy adhesive. Most of these techniques are, however, difficult to apply under clinical settings in dentistry. Information concerning the potential and limitations of this material in bonding to dental materials is scarce if not to say inexistent.
Therefore, it was the aim of the present investigation to assess possible bonding techniques of PEEK to dental composite resin materials. We hypothesized that pre-treatment with either mechanical and/or chemical measures would result in possible adhesion to PEEK, irrespective whether an adhesive/composite or a universal composite resin cement was used.
2
Materials and methods
2.1
Specimen preparation
One hundred and fifty PEEK disks (PEEK-CLASSIX, Villmergen, Switzerland) with a diameter of 10 mm and a thickness of 2 mm were embedded in self-curing acrylic resin (ScandiQuick, Scandia, Hagen, Germany) and a standard surface was created by means of a polisher (Reco GMT 5350, Le Leux, Switzerland) with a series of SiC-papers up to P4000 grit. Before initiating the bonding procedure, the specimens were cleaned for 10 min in an ultrasonic water bath (Bransonic Ultrasonic Cleaner 3510 E-DTH, Branson, Danbury, USA) and air-dried.
The PEEK surfaces were then treated as follows ( n = 30 for each pre-treatment group):
- (A)
No treatment.
- (B)
Acid etching with sulfuric acid (98%) for 1 min. Careful rinsing with de-ionized water for 1 min.
- (C)
Sandblasting with alumina with a mean particle size of 50 μm (LEMAT NT4, Wassermann, Germany) for 10 s at a pressure of 2 bar and at a distance of 10 mm between the nozzle and the surface
- (D)
Sandblasting with alumina with a mean particle size of 110 μm as described under point C
- (E)
Silica coating (Rocatec Delta, 3M ESPE, Seefeld, Germany) with Rocatec Pre (3M ESPE) for 10 s and subsequent Rocatec Plus (3M ESPE) for 12 s. Application of ESPE Sil (3M ESPE) and air-drying for 5 min
Titanium specimens (cp-titanium grade 4) with the same dimensions were prepared as control, following the same procedure as described above under point (C), i.e. polishing and subsequent sandblasting with 50 μm alumina.
Two additional specimens were produced of each surface treatment group and analyzed by means of SEM (CS4, CamScan, Waterbeach, UK) to assess the surface topography after the respective surface pre-treatment. Samples were at a magnification of 2000×.
2.2
Shear bond strength testing
Fifteen samples of each pre-treatment group were randomly allocated to one of the following two bonding procedures/materials ( Table 1 ):
- –
Application of the universal composite resin cement RelyX Unicem (3M ESPE)
- –
Application of an unfilled resin material (Heliobond, Ivoclar Vivadent, Schaan, Liechtenstein) and a fine hybrid composite resin material (Tetric, Vivadent).
An acrylic hollow cylinder with an inner diameter of 3.1 mm and an outer diameter of 4.0 mm was pressed onto the different surfaces by means of a special bonding device ( Fig. 1 ), the universal cement was filled into the opening of the cylinder and pressed with a force of 100 N and polymerized for 40 s (Elipar Freelight 2, 3M ESPE; 1000 mW/cm 2 ). Thereafter the specimens were carefully removed from the device. When the adhesive composite resin material was used, the bonding agent was applied first, blown to a thin layer with an oil-fee air and after carefully removing all excess material the material was light-cured for 40 s. Subsequently, the composite resin material was applied and light-cured for additional 40 s.
| Material | Composition |
|---|---|
| RelyX Unicem LOT 325899 | Powder: glass fillers, silica, calcium hydroxide, self-cure initiators, pigments, light-cure initiators; liquid: methacrylated phosphoric esters, dimethacrylates, acetate, stabilizers, self-cure initiators |
| Heliobond LOT K04445 | BisGMA ((1-methylethylidene)bis[4,1-phenyleneoxy(2-hydroxy-3,1-propanediyl)] bismethacrylate), TEGDMA, UDMA (urethanedimethacrylate: 1,6-dimethacryl-ethyl-oxy-carbonylamino-2,4,4-trimethylhexane) |
| Tetric LOT J27775 | BisGMA, UDMA, TEGDMA, photo-initiators, barium glass, ytterbium trifluoride, dispersed silica |
Following bonding procedure the specimens were stored in distilled water at 37 °C for 24 h.
The shear bond strength was tested with a universal testing machine (Z010, Zwick, Ulm, Germany). The specimens were positioned in the sample holder with the treated sample surface parallel to the loading piston in a distance of 200 μm. The loading piston had a chisel configuration and load was applied with a crosshead speed of 1 mm/min. Load at failure was recorded and shear strength values were calculated according to the equation σ = F / A , where σ is the shear bond strength, F the load at failure (N) and A represents the adhesive area (mm 2 ).
For the fracture analysis, the debonded area was examined with a stereomicroscope at 40× magnifications (M3B, Wild, Heerbrugg, Switzerland). Failure was considered: adhesive – if the cement/resin was dislodged from PEEK / titanium ; cohesive in the cement/resin – if the fracture occurred only in the cement/resin; and cohesive in PEEK / titanium – if the fracture occurred only in the PEEK / titanium .
The adhesive interface and adhesive luting material penetration, i.e. possible tag formation was analyzed by SEM (CS4, CamScan, Waterbeach, UK). For this purpose, two notches were prepared at the specimens and the specimens were fractured. The specimens were examined at a magnification of 150–2000×.
2.3
Data presentation and analysis
Statistical tests were performed with StatView Version 5 (Abacus Concepts, Berkley, CA). Mean values and standard deviations were calculated and results of the shear bond strength measurements presented as bar charts with standard deviations. One-way ANOVA followed by a post hoc Scheffé test and unpaired t -tests were applied to find differences between the experimental treatments. The level of significance was set at 5%.
2
Materials and methods
2.1
Specimen preparation
One hundred and fifty PEEK disks (PEEK-CLASSIX, Villmergen, Switzerland) with a diameter of 10 mm and a thickness of 2 mm were embedded in self-curing acrylic resin (ScandiQuick, Scandia, Hagen, Germany) and a standard surface was created by means of a polisher (Reco GMT 5350, Le Leux, Switzerland) with a series of SiC-papers up to P4000 grit. Before initiating the bonding procedure, the specimens were cleaned for 10 min in an ultrasonic water bath (Bransonic Ultrasonic Cleaner 3510 E-DTH, Branson, Danbury, USA) and air-dried.
The PEEK surfaces were then treated as follows ( n = 30 for each pre-treatment group):
- (A)
No treatment.
- (B)
Acid etching with sulfuric acid (98%) for 1 min. Careful rinsing with de-ionized water for 1 min.
- (C)
Sandblasting with alumina with a mean particle size of 50 μm (LEMAT NT4, Wassermann, Germany) for 10 s at a pressure of 2 bar and at a distance of 10 mm between the nozzle and the surface
- (D)
Sandblasting with alumina with a mean particle size of 110 μm as described under point C
- (E)
Silica coating (Rocatec Delta, 3M ESPE, Seefeld, Germany) with Rocatec Pre (3M ESPE) for 10 s and subsequent Rocatec Plus (3M ESPE) for 12 s. Application of ESPE Sil (3M ESPE) and air-drying for 5 min
Titanium specimens (cp-titanium grade 4) with the same dimensions were prepared as control, following the same procedure as described above under point (C), i.e. polishing and subsequent sandblasting with 50 μm alumina.
Two additional specimens were produced of each surface treatment group and analyzed by means of SEM (CS4, CamScan, Waterbeach, UK) to assess the surface topography after the respective surface pre-treatment. Samples were at a magnification of 2000×.
2.2
Shear bond strength testing
Fifteen samples of each pre-treatment group were randomly allocated to one of the following two bonding procedures/materials ( Table 1 ):
- –
Application of the universal composite resin cement RelyX Unicem (3M ESPE)
- –
Application of an unfilled resin material (Heliobond, Ivoclar Vivadent, Schaan, Liechtenstein) and a fine hybrid composite resin material (Tetric, Vivadent).
An acrylic hollow cylinder with an inner diameter of 3.1 mm and an outer diameter of 4.0 mm was pressed onto the different surfaces by means of a special bonding device ( Fig. 1 ), the universal cement was filled into the opening of the cylinder and pressed with a force of 100 N and polymerized for 40 s (Elipar Freelight 2, 3M ESPE; 1000 mW/cm 2 ). Thereafter the specimens were carefully removed from the device. When the adhesive composite resin material was used, the bonding agent was applied first, blown to a thin layer with an oil-fee air and after carefully removing all excess material the material was light-cured for 40 s. Subsequently, the composite resin material was applied and light-cured for additional 40 s.
