The effects of surface treatments on tensile bond strength of polyether-ketone-ketone (PEKK) to veneering resin

Clinical performance of custom-milled polyetherketoneketone (PEKK) posts and cores: A 12-month follow-up randomized controlled pilot study

OBJECTIVES

Comparing the survival rate and the cumulative success rates of custom-milled polyetherketone ketone posts and cores (MPP) with prefabricated fiber posts (PFP) in restoring compromised endodontically treated premolars.

MATERIAL AND METHODS

This was a randomized, double-blind, parallel, two-arm controlled pilot study. A total of 24 patients (12 males, 12 females), each had a compromised lower premolar, needed a root canal treatment and to be restored with post and core. Patients were randomly allocated into two groups, MPP-group: restored with MPP, and PFP-group: restored with PFP and composite cores. After that, premolars were restored with single porcelain fused to metal (PFM) crowns. Clinical and radiographic follow-ups were conducted after 3, 6, and 12 months. The Kaplan-Meier, log-Rank, and χ2 tests were used to investigate differences between the two groups at the 0.05 significance level.

RESULTS

The survival rate after 12 months in the MPP and PFP groups was 66.7% and 100%, respectively. Meanwhile, the cumulative success rates were 63.6% and 100% in the same order. The log-rank test showed a significant difference between the two groups (p = .031). The difference in cumulative success rates was also significant, as the χ2 test revealed (p = .011).

CONCLUSION

The PFP group showed a higher success rate than the MPP group and according to the failure types, PEKK posts seem to be inferior to PFP in terms of the mechanical properties and bonding to resin mechanism.

TRIAL REGISTRATION

ISRCTN, ISRCTN13456471. October, 14, 2019. (https://doi.org/10.1186/ISRCTN13456471ISRCTN13456471).

New adhesive protocol improves shear bond strength of Polyetherketoneketone (PEKK)

OBJECTIVE

Inert surface of Polyetherketoneketone (PEKK) jeopardizes resin bonding. This study aimed to present a new adhesive protocol to improve PEKK bonding.

METHODS

A total of 360 PEKK blocks were milled, polished (maximum roughness of 0.20 µm), and randomly assigned to groups. The new protocol was applied (n = 36) and compared to conventional treatments (no treatment; sandblasting (110-µm Al2O3 and silica); no adhesive; Visiolink (Bredent); and PEKKbond (AnaxDent)) (n = 36). For the new protocol, the surface was blasted (110 µm Al2O3 and 96% isopropyl alcohol at 60 psi), followed by 96% isopropyl alcohol washing, and air drying. PEKKbond was applied (dried for 3 min at 77 °C), followed by Visiolink (dried for 3 min at 60 °C); both light-cured for 3 min (800 mW/cm2). Preopaque (GC Europe) and Opaque (AnaxDent) were applied and light-cured (5 min). Morphological topography was analyzed, and flowable gingiva-colored composite (AnaxGum, AnaxDent) was bonded. All specimens were aged for 24 h and thermocycled (5000 cycles, 5-55 °C). Shear bond strength (SBS) was measured (MPa) and data were analyzed by two-way ANOVA, Tukey, and Weibull moduli estimation (α = 0.05).

RESULTS

The highest SBS values were found in the new protocol (p < 0.05), regardless of aging. Thermocycling reduced SBS (p < 0.05), while Al2O3 and PEKKbond produced higher SBS values than silica and Visiolink, respectively (p < 0.05).

SIGNIFICANCE

The new protocol strongly improves PEKK adhesiveness, and this can reflect in the longevity of prostheses.

Improving Surface Properties of PEEK for Dental Applications by Using Piranha Solution

Background

"Polyetheretherketone (PEEK)" is a biocompatible, high-strength polymer that is well-suited for use in dental applications due to its unique properties. However, achieving good adhesion between PEEK and hydrophilic materials such as dental adhesives or cement can be challenging. Also, this hydrophobicity may affect the use of PEEK as an implant material. Surface treatment or conditioning is often necessary to improve surface properties. The piranha solution is the treatment of choice to be explored for this purpose.

Methods

PEEK disks of 10 mm diameter and 2 mm thickness were used in this study. Those samples were divided into five groups (each group has five samples). The first is the control group, in which no acid treatment was used; the second group undergoes sulfuric acid treatment. The remaining three groups were treated with Piranha solution; each group used a different concentration (1 : 3, 1 : 5, and 1 : 7 hydrogen peroxide to sulfuric acid, respectively). The period of treatment was 60 s for all groups. Wettability and surface roughness tests were done for the five groups. In statistical analysis, Shapiro-Wilk test was used to check the assumption of normality and to determine the statistical significance among groups; a one-way analysis of variance was employed. Subsequently, for multiple comparisons, Tukey's honestly significant difference post hoc test was performed.

Results

The Piranha solution treatment groups showed a higher wettability compared to the control group and the group treated with sulfuric acid. Additionally, the Piranha solution treatment with a higher concentration of hydrogen peroxide (1 : 3) resulted in greater improvement in surface roughness compared to the control group and the lower concentration groups (1 : 5 and 1 : 7), while the sulfuric acid treated group showed the highest surface roughness.

Conclusion

The results of this study suggest that the piranha solution can be an effective method for improving the surface characteristics of PEEK to be used in different dental applications, especially as a dental implant material, due to the increase in wettability and surface roughness.

Determination of Shear Bond Strength between PEEK Composites and Veneering Composites for the Production of Dental Restorations

We studied the shear bond strength (SBS) of two PEEK composites (BioHPP, BioHPP plus) with three veneering composites: Visio.lign, SR Nexco and VITA VM LC, depending on the surface treatment: untreated, sandblasted with 110 μm Al₂O₃, sandblasted and cleaned ultrasonically in 80% ethanol, with or without adhesive Visio.link, with applied Visio.link and MKZ primer. For the BioHPP plus, differential scanning calorimetry (DSC) revealed a slightly lower glass transition temperature (T_g 150.4 ± 0.4 °C) and higher melting temperature (T_m 339.4 ± 0.6 °C) than those of BioHPP (T_g 151.3 ± 1.3 °C, T_m 338.7 ± 0.2 °C). The dynamical mechanical analysis (DMA) revealed a slightly higher storage modulus of BioHPP (E' 4.258 ± 0.093 GPa) than of BioHPP plus (E' 4.193 ± 0.09 GPa). The roughness was the highest for the untreated BioHPP plus, and the lowest for the polished BioHPP. The highest hydrophobicity was achieved on the sandblasted BioHPP plus, whereas the highest hydrophilicity was found on the untreated BioHPP. The highest SBSs were determined for BioHPP and Visio.lign, adhesive Visio.link (26.31 ± 4.17 MPa) or MKZ primer (25.59 ± 3.17 MPa), with VITA VM LC, MKZ primer and Visio.link (25.51 ± 1.94 MPa), and ultrasonically cleaned, with Visio.link (26.28 ± 2.94 MPa). For BioHPP plus, the highest SBS was determined for a sandblasted surface, cleaned ultrasonically, with the SR Nexco and Visio.link (23.39 ± 2.80 MPa).

Comparing the shear bond strength of veneering materials to the PAEKs after surface treatments

Background

This study aimed to evaluate the impact of various surface treatments on the shear bond strength (SBS) of polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) polymers to indirect laboratory composite (ILC) and lithium disilicate ceramic (LDC) veneering materials.

Methods

Polymer specimens (7 × 7x2 mm) were sectioned from PEEK and PEKK discs (N = 294) and randomly allocated to 7 groups (n = 20); untreated (Cnt), plasma (Pls), 98% sulfuric acid (Sa), sandblasting with 110 µm Al2O3 (Sb), tribochemical silica coating with 110 µm silica modified Al2O3 (Tbc), Sb + Sa, Tbc + Sa. Scanning electron microscopy assessments were performed on one sample of each treatment group, and veneering materials were applied to the remaining specimens (n = 10). The specimens were subjected to the SBS test after being soaked in distilled water (24 h, 37 °C). Three-way ANOVA, independent sample t-test, and Tukey HSD test were performed for statistical analyses (α = .05).

Results

The surface treatment, polymer, veneering material types, and their interactions were significant on SBS results according to the 3-way ANOVA (p < 0.001). The SBS values of ILC veneered groups were significantly higher than LDC groups, regardless of surface treatment and polymer type (p < 0.05). The highest SBS values were obtained for Sa-applied ILC veneered PEEK (21.55 ± 1.45 MPa) and PEKK (17.04 ± 1.99 MPa) polymer groups (p < 0.05).

Conclusion

The effect of surface treatment and veneering materials may be significant on the SBS values of PAEKs. Therefore, the application parameters of surface treatments should be more specified for the applied veneering material and polymer type.

Surface Characteristics and Adhesion of Veneering Composite Resin to PAEK-Based Substructure Restorative Materials

PURPOSE

To evaluate and compare the shear bond strength (SBS) of composite veneering material to polyetherketoneketone (PEKK), polyetheretherketone (PEEK), zirconia (YZ), and nickel-chromium alloy (NiCr) substructure restorative materials.

MATERIALS AND METHODS

Forty samples (12 × 2 mm) were prepared from four materials: PEKK, PEEK, zirconia, and NiCr alloy (n = 10). The Vickers hardness was evaluated before preparing the surface for bonding by shot-blasting using 110 μm Al₂ O₃ particles. The surface roughness (Ra) of each sample was determined using a noncontact optical profilometer. The veneering resin was bonded onto each sample following primer application. The prepared samples were then subjected to an SBS test using a universal testing machine at 0.5 mm/min crosshead speed. Failure modes and surface topography following debonding were assessed. The data were statistically analyzed using ANOVA and Tukey's post-hoc comparison test (p < 0.05).  RESULTS: The highest and lowest mean surface roughness was observed in PEEK (3.45 ±0.13 μm) and NiCr (1.87 ±0.07 μm) materials, respectively. A significant difference in roughness values was observed between the materials except for NiCr and YZ (p = 0.547). Concerning SBS, PEEK and NiCr exhibited the highest (16.23 ±0.96 MPa) and lowest (10.1 ±0.63 MPa) values. The mean difference in SBS indicated a statistically significant difference between the material groups (p < 0.01).

CONCLUSIONS

PEKK materials demonstrated significantly lower SBS than PEEK and significantly higher SBS values than conventional zirconia and alloy materials. A positive and significant correlation between mean roughness and SBS was observed, but the causality could be either intrinsic to the material or the roughness.

The effects of HAp coating layer on mechanical and optical properties at bonding interface of high-performance polymers

PURPOSE

The effect of hydroxyapatite (HAp) coating layer on mechanical and optical properties at bonding interface of high-performance polymers (HPPs) used in computer-aided design (CAD)/computer-aided manufacture (CAM) technology was investigated in this in vitro study.

MATERIALS AND METHODS

Two hundred-twenty specimens were divided into two material groups (n = 110): polyetheretherketone (PEEK, KERA® starPEEK) and polyetherketoneketone (PEKK, Pekkton® ivory). For mechanical testing, each group was divided into five surface pretreatment subgroups and a control group (n = 10): HAp coating (1%,3%, 5%, and 10% concentrations) and sandblasting with 110-μm Al₂O₃ particles. For optical testing, each group was divided into five subgroups (n = 10): HAp coating (1%, 3%, 5%, and 10% concentrations) and control. The effects of the HAp coating on the optical changes and shear bond strength (SBS) of the specimens were investigated. Data was statistically analyzed by one-way ANOVA and Tukey's post-hoc test. Failure modes and surface properties of the specimens were examined by scanning electron microscopy (SEM) and coupled electron dispersive spectroscopy (EDS).

RESULTS

Average translucency and color change values increased with increasing HAp coating concentration in HPPs. As a result of the data, statistically significant differences were observed in terms of the effect of the HAp coating on SBS of HPPs (p < 0.05). Failure modes were examined, and mixed failure mode was observed.

CONCLUSION

HAp coating can contribute to the improvement of both the optical properties and bond strength of the HPPs to resin composite.

CLINICAL SIGNIFICANCE

Adhesion and color problems of high performance polymers are still under discussion. In order to solve these problems, generally focused on surface modifications of these polymers, but the effect of the HAp coating has not been investigated.

Surface Modifications of High-Performance Polymer Polyetheretherketone (PEEK) to Improve Its Biological Performance in Dentistry

This comprehensive review focuses on polyetheretherketone (PEEK), a synthetic thermoplastic polymer, for applications in dentistry. As a high-performance polymer, PEEK is intrinsically robust yet biocompatible, making it an ideal substitute for titanium-the current gold standard in dentistry. PEEK, however, is also inert due to its low surface energy and brings challenges when employed in dentistry. Inert PEEK often falls short of achieving a few critical requirements of clinical dental materials, such as adhesiveness, osseoconductivity, antibacterial properties, and resistance to tribocorrosion. This study aims to review these properties and explore the various surface modification strategies that enhance the performance of PEEK. Literatures searches were conducted on Google Scholar, Research Gate, and PubMed databases using PEEK, polyetheretherketone, osseointegration of PEEK, PEEK in dentistry, tribology of PEEK, surface modifications, dental applications, bonding strength, surface topography, adhesive in dentistry, and dental implant as keywords. Literature on the topics of surface modification to increase adhesiveness, tribology, and osseointegration of PEEK were included in the review. The unavailability of full texts was considered when excluding literature. Surface modifications via chemical strategies (such as sulfonation, plasma treatment, UV treatment, surface coating, surface polymerization, etc.) and/or physical approaches (such as sandblasting, laser treatment, accelerated neutral atom beam, layer-by-layer assembly, particle leaching, etc.) discussed in the literature are summarized and compared. Further, approaches such as the incorporation of bioactive materials, e.g., osteogenic agents, antibacterial agents, etc., to enhance the abovementioned desired properties are explored. This review presents surface modification as a critical and essential approach to enhance the biological performance of PEEK in dentistry by retaining its mechanical robustness.

Effect of Carbon Nanotubes on the Mechanical, Crystallization, Electrical and Thermal Conductivity Properties of CNT/CCF/PEKK Composites

Carbon nanotube/continuous carbon fiber–reinforced poly(etherketoneketone) (CNT/CCF/PEKK) prepreg tapes were prepared by the wet powder impregnation method, and then the prepreg tapes were molded into laminates. The effects of carbon nanotubes on the mechanical properties, conductivity, thermal conductivity and crystallinity of the composites were studied by universal testing machine, thermal conductivity and resistivity tester, dynamic mechanical analyzer (DMA) and differential scanning calorimeter (DSC). The results show that when the content of carbon nanotubes is 0.5 wt% (relative to the mass of PEKK resin, the same below), the flexural strength and interlaminar shear strength of the laminates reach the maximum, which are increased by 15.99% and 18.16%, respectively, compared with the laminates without carbon nanotubes. The results of conductivity and thermal conductivity show that the higher the content of carbon nanotubes, the better the conductivity and thermal conductivity of the material. DSC results show that the addition of CNT promoted the crystallization of PEKK in the material and decreased the cold crystallization of PEKK. DMA results show that the deformation resistance of the material can be improved by adding an appropriate amount of CNT and the bonding between CF and PEKK can be enhanced, while excessive CNT destroys this phenomenon.

Strength and flexibility of lithium disilicate bonded to polyetherketoneketone

STATEMENT OF PROBLEM

Polyetherketoneketone (PEKK) is a high-performance polymer gaining popularity in dentistry for the fabrication of crowns, fixed partial dentures, removable partial denture frameworks, and frameworks for implant-supported fixed complete dentures. Despite a lack of performance data, lithium disilicate crowns have been bonded to retentive elements in PEKK frameworks.

PURPOSE

The purpose of this in vitro study was to compare the bond strengths and flexibility of lithium disilicate to PEKK or zirconia.

MATERIAL AND METHODS

Forty-five PEKK, 15 zirconia, and 60 lithium disilicate beam-shaped specimens (12.5×2×2 mm) were fabricated. The ends of the PEKK beams were subjected to 3 different surface treatments before the application and light polymerization of a primer: 50-μm aluminum oxide airborne-particle abrasion, nonthermal air plasma, and argon-oxygen plasma. The zirconia specimen bonding surfaces were prepared with 50-μm aluminum oxide airborne-particle abrasion and the application of primer. Lithium disilicate specimens were etched with 4.5% hydrofluoric acid, and primer was applied. The lithium disilicate specimens were luted with an adhesive resin cement to the PEKK and zirconia specimens by using light-activated and chemically activated polymerization. Fifteen monolithic specimens of PEKK, lithium disilicate, and zirconia (25×2×2 mm) were also fabricated. All specimens were incubated overnight in 100% humidity before testing. Bonded and monolithic specimens were loaded in a universal testing machine, and 4-point bend tests were conducted until failure (n=15). The flexural modulus and strength were calculated and statistically analyzed with 1-way analysis of variance and Student-Newman-Keuls post hoc tests (α=.05).

RESULTS

All bonded specimens failed at the adhesive interface. The zirconia-lithium disilicate bond strength was approximately twice that of the strongest group of PEKK (airborne-particle abrasion group) bonded to lithium disilicate (42 ±12 MPa and 24 ±13 MPa, respectively) and was approximately 9 times more rigid (71 ±19 GPa and 8 ±2 GPa, respectively). Monolithic PEKK fractured at 238 ±22 MPa, monolithic zirconia at 771 ±128 MPa, and monolithic lithium disilicate at 173 ±26 MPa. Monolithic PEKK was approximately 30 times more flexible than monolithic zirconia (6 ±1 GPa and 178 ±16 GPa, respectively). All values were statistically significantly different (P<.05), except for the bond strength between lithium disilicate and PEKK treated with airborne-particle abrasion and nonthermal air plasma and the flexural moduli of PEKK to lithium disilicate.

CONCLUSIONS

Bond strength between PEKK and lithium disilicate was significantly weaker than that between zirconia and lithium disilicate. Monolithic PEKK was significantly more flexible than monolithic zirconia.

Effects of surface treatments on the bonding properties of polyetherketoneketone to dentin: An in vitro study

STATEMENT OF PROBLEM

Polyetherketoneketone (PEKK) has been recently introduced as a dental material for fixed dental prostheses. However, how surface treatments affect the bonding of PEKK to dentin is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the effects of airborne-particle abrasion and acid etching on the bonding of PEKK to dentin.

MATERIAL AND METHODS

Eighty-four PEKK specimens were fabricated, polished, and divided into 6 groups (n=14): no treatment (group NT), airborne-particle abrasion with 110-μm alumina particles (group Al), 98% sulfuric acid etching for 5 seconds (group SA5), 98% sulfuric acid etching for 30 seconds (group SA30), 98% sulfuric acid etching for 60 seconds (group SA60), and airborne-particle abrasion plus 98% sulfuric acid for 5 seconds (group AlSA5). Sixty PEKK specimens (n=10) were fabricated for the shear bond test. Another 24 PEKK specimens (n=4) were fabricated for surface element analysis and morphological observations. For each group, 2 specimens after surface treatments were randomly selected to examine scanning electron microscope (SEM) observations and surface element analysis. Another 2 specimens after bonding were randomly selected to examine cross-sectional observations. Airborne-particle abrasion with 110-μm alumina particles was performed to cobalt-chromium (Co-Cr) specimens (group Co-Cr, n=10). A light-polymerizing polymethylmethacrylate and composite resin primer (visio.link) was applied to the treated PEKK specimens and bonded with a resin cement (RelyX Ultimate) to dentin. The Co-Cr specimens were bonded with the resin cement to dentin. The shear bond strengths of all groups were tested by using a universal testing machine, and fracture analysis was performed. A statistical analysis was performed by using 1-way ANOVA, followed by the Student-Newman-Keuls-q post hoc test (α=.05).

RESULTS

The shear bond strengths of groups SA5 and AlSA5 were higher than those of groups NT, Al, SA30, SA60, and Co-Cr (P＜.05). Group SA5 achieved the highest shear bond strength (16.84 ±1.84 MPa). The SEM observations showed that after surface treatments, groups SA5 and AlSA5 had a uniform sponge shape with small pores, while groups SA30 and SA60 had a collapsed shape with large pits and pores. The sulfur element content and H₂SO₄-etched thicknesses of groups SA30 and SA60 were higher than those of groups SA5 and AlSA5. The cross-sectional SEM observations of groups SA30 and SA60 after bonding revealed that H₂SO₄-etched pores were deeper and not filled with the bonding material.

CONCLUSIONS

Compared with airborne-particle abrasion, the 98% sulfuric acid etching significantly improved the shear bond strength of PEKK to dentin. The surface treatment of 98% sulfuric acid etching for 5 seconds led to the high bond strength of PEKK to dentin, which meets the requirements for clinical use.

Effect of surface treatment and manufacturing process on the shear bond strength of veneering composite resin to polyetherketoneketone (PEKK) and polyetheretherketone (PEEK)

STATEMENT OF PROBLEM

Polyaryletherketones (PAEKs) are high-performance polymer materials in which polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) are the most used. Although mechanical and shear bonding strength tests have been performed on the 2 materials, studies on the influence of processing on bonding are scarce.

PURPOSE

The purpose of this in vitro study was to determine the influence of the surface treatment and the manufacturing process on the shear bond strength of veneering composite resin to PEKK and PEEK.

MATERIAL AND METHODS

Thirty pressed PEKK, 30 milled PEKK, and 30 milled PEEK specimens were distributed in 6 groups (n=13) as per the manufacturing process and treatment surface. The specimens were either treated with airborne-particle abrasion with 110-μm aluminum oxide, or no surface treatment was applied. Moreover, the PEKK specimens were grouped regarding their manufacturing process, as either milled or heat-pressed. The specimens were all bonded by using a methyl methacrylate-based adhesive (visio.link), and composite resin (Gradia Revolution 2) was bonded to the specimens. An Instron universal machine was used to calculate the shear bond strength between the PEEK or PEKK and the composite resin. Two specimens from each group had their topography modification assessed with a scanning electron microscope. Statistical analysis was performed by using a 3-way ANOVA for multiple comparisons (α=0.05) RESULTS: The groups that were surface treated with 110-μm aluminum oxide (Al₂O₃) before bonding showed significantly higher shear bond strength (P=.001) than the other groups. However, no statistically significant difference was observed among the groups, regardless of the manufacturing process (milled or heat-pressed) (P=.607).

CONCLUSIONS

PEEK and PEKK surfaces treated with 110-μm aluminum oxide airborne-particle abrasion displayed better shear bond strength to composite resin. The manufacturing process (milled or heat-pressed) did not significantly affect the bond strength of PEKK when subjected to the same bonding process.

Influence of chairside surface treatments on the shear bond strength of PEKK polymer to veneering resin materials: An in vitro study

STATEMENT OF PROBLEM

High-performance thermoplastics have been adopted as an alternative restorative material to metal or ceramics. However, a straightforward surface modification process to provide a durable bond strength between the polymer and the veneering material is lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the shear bond strength (SBS) of different veneering resin materials to polyetherketoneketone (PEKK) after different surface treatments.

MATERIAL AND METHODS

Rectangular (7×7×2 mm) PEKK specimens (N=120) were randomly allocated to the following 6 groups (n=20): untreated (Cnt); nonthermal plasma (NTP) treated; tribochemical silica airborne-particle abrasion with 30-μm silica-modified Al₂O₃ (Tbc); abraded with a coarse-grit diamond rotary instrument (Ab); tribochemical silica airborne-particle abrasion + plasma treated (Tbc_NTP); abraded + plasma treated (Ab_NTP). After a bonding agent (PEKK Bond) was applied to the specimens, each group was divided into 2 subgroups according to the applied veneering resin materials: polymethylmethacrylate (PMMA) and nanohybrid composite resin (NHC, n=10). The specimens were stored in water for 24 hours at 37 °C and subjected to the SBS test by using a universal testing machine, and failure modes were evaluated using a stereomicroscope. Two-way analysis of variance (ANOVA) was performed followed by the Tukey honestly significant difference (HSD) test to statistically analyze the data (α=.05).

RESULTS

The 2-way ANOVA showed that surface treatment methods, veneering material, and their interactions were significantly different on the SBS values (P<.001). The highest SBS values were determined for the Tbc and Tbc_NTP treatment groups not only for PMMA (10.71 to 11.63 MPa) but also for NHC (19.80 to 20.60 MPa) veneering resin materials (P<.05).

CONCLUSIONS

The bonding capacity of PEKK to the PMMA and NHC veneering resin materials can be significantly improved by using tribochemical silica airborne-particle abrasion alone or with nonthermal plasma surface treatment techniques. Furthermore, using NHC veneering resin material is recommended over PMMA.

Complete denture fabrication with polyetherketoneketone as a framework material: A clinical report

This clinical report describes the fabrication of conventional complete dentures with polyetherketoneketone (PEKK) frameworks made with computer-aided design and computer-aided manufacturing (CAD-CAM). No biologic or prosthetic complications were observed at the 1-year follow-up.

Review on Development and Dental Applications of Polyetheretherketone-Based Biomaterials and Restorations

Polyetheretherketone (PEEK) is an important high-performance thermoplastic. Its excellent strength, stiffness, toughness, fatigue resistance, biocompatibility, chemical stability and radiolucency have made PEEK attractive in dental and orthopedic applications. However, PEEK has an inherently hydrophobic and chemically inert surface, which has restricted its widespread use in clinical applications, especially in bonding with dental resin composites. Cutting edge research on novel methods to improve PEEK applications in dentistry, including oral implant, prosthodontics and orthodontics, is reviewed in this article. In addition, this article also discusses innovative surface modifications of PEEK, which are a focus area of active investigations. Furthermore, this article also discusses the necessary future studies and clinical trials for the use of PEEK in the human oral environment to investigate its feasibility and long-term performance.

The Effect of Different Cleaning Protocols of Polymer-Based Prosthetic Materials on the Behavior of Human Gingival Fibroblasts

Dental implant abutment and prosthetic materials, their surface treatment, and cleaning modalities are important factors for the formation of a peri-implant soft tissue seal and long-term stability of bone around the implant. This study aimed to investigate the influence of a polymeric material surface cleaning method on the surface roughness, water contact angle, and human gingival fibroblasts (HGF) proliferation. Polymeric materials tested: two types of milled polymethylmethacrylate (PMMA-Ker and PMMA-Bre), three-dimensionally (3D) printed polymethylmethacrylate (PMMA-3D), polyetheretherketone (PEEK), and polyetherketoneketone (PEKK). Titanium (Ti) and zirconia oxide ceramics (ZrO-HT) were used as positive controls. A conventional surface cleaning protocol (CCP) was compared to a multi-step research cleaning method (RCP). Application of the RCP method allowed to reduce S_a values in all groups from 0.14-0.28 µm to 0.08-0.17 µm (p < 0.05 in PMMA-Ker and PEEK groups). Moreover, the water contact angle increased in all groups from 74-91° to 83-101° (p < 0.05 in the PEKK group), except ZrO-HT-it was reduced from 98.7 ± 4.5° to 69.9 ± 6.4° (p < 0.05). CCP resulted in higher variability of HGF viability after 48 and 72 h. RCP application led to higher HGF viability in PMMA-3D and PEKK groups after 48 h, but lower for the PMMA-Ker group (p < 0.05). After 72 h, no significant differences in HGF viability between both cleaning methods were observed. It can be concluded that the cleaning method of the polymeric materials affected surface roughness, contact angle, and HGF viability at 48 h.

Polyetherketoneketone (PEKK): An emerging biomaterial for oral implants and dental prostheses

Polyetherketoneketone (PEKK) is a new evolving polymeric material. The present article comprehensively reviewed an overview of various applications of PEKK in prosthodontics and oral implantology, highlighting its prospects for clinical applications. PEKK biomaterials is an elastic material with good shock absorbance and fracture resistance and present ultra-high performance among all thermoplastic composites for excellent mechanical strength, chemical resistance, and high thermal stability. Available articles on PEKK for dental applications were reviewed from January 1957 to August 2020) using MEDLINE/PubMed, Web of Science, and ScienceDirect resources. PEKK presents suitable physical, mechanical, and chemical properties for applications in prosthodontics and oral implantology. PEKK has good potential for a wide range of dental applications, including tooth restorations, crowns, bridge, endoposts, denture framework, implant-supported fixed prosthesis, and dental implants. PEKK dental implants have shown lesser stress shielding compared to titanium for dental implant applications. Further modifications and improving material properties can result in broader applications in the field of dentistry. Long term evaluations are needed as PEKK is recently applied in dentistry, and there are limited studies published on PEKK.

The impact of non-thermal plasma on the adhesion of polyetherketoneketone (PEKK) to a veneering composite system

The PEKK material can be used in prosthodontics for framework manufacturing and is commonly laminated with veneering composites to achieve a better esthetics. Various surface treatment methods including sandblasting, etching, laser and cold plasma treatments were reported to enhance the adhesive properties of dental polymers. Both tensile and shear bond test were employed to quantify the bond strength between PEKK and veneering composites. The present in vitro study aims to evaluate the influence of acetylene, argon, air, nitrogen and oxygen plasma on the shear bond strength between PEKK and one veneering composite. Firstly, to determine which bond test type should be applied, n = 40 PEKK specimens were treated with argon plasma. Both shear and tensile bond tests were performed and compared to the control group (n = 40). In shear bond testing, values were 8.14 ± 1.70 MPa for Argon plasma while 5.83 ± 1.42 MPa for control group. In tensile bond testing, Argon plasma 1.50 ± 0.51 MPa while control group 0.58 ± 0.50 MPa. Afterwards n = 160 PEKK specimens were treated with rocatec sandblasting (n = 20), adhesive (n = 20), acetylene (n = 20), argon (n = 20), air (n = 20), nitrogen (n = 20), oxygen (n = 20) plasma types and compared to the untreated control group (n = 20) using shear bond strength test (SBS). Additionally surface roughness and scanning electron microscopy analyses were performed. The following SBS values were revealed: 10.22 ± 1.06 MPa for rocatec; 9.89 ± 3.08 MPa for acetylene, 9.16 ± 1.48 MPa for adhesive, 7.54 ± 1.52 MPa for argon, 7.09 ± 1.99 MPa for air, 7.03 ± 1.48 MPa for nitrogen, 5.69 ± 1.59 MPa for oxygen plasma types and 4.71 ± 1.54 MPa for the control group. All groups, except control group, showed SBS over 5 MPa, which means that they are suitable for the clinical application, according to ISO 10477. Acetylene showed the highest SBS among all plasma types (p < 0.0001), which was on a level of rocatec sandblasting group. Rocatec and acetylene groups demonstrated Ra values significantly different to the reference group (p < 0.0001). Plasma treatment especially with acetylene gas can be an effective more convenient surface treatment method for strengthening the bond strength between PEKK and veneering composites than traditional sandblasting/adhesive treatment.

Fatigue behavior and damage modes of high performance poly-ether-ketone-ketone PEKK bilayered crowns

OBJECTIVES

To evaluate and compare the fatigue behavior (fatigue limit and fatigue life) and damage modes of high-performance poly-ether-ketone-ketone (PEKK), zirconia and alloy bilayered crowns.

MATERIALS AND METHODS

A total of 110 crowns (n = 50 for fatigue limit and n = 60 for fatigue life) were fabricated and used in this study. Pekkton® ivory discs, yttrium stabilized zirconia blanks and NiCr casting alloy were used to produce the respective PEKK, zirconia and alloy copings for crown fabrication. The prepared crowns were veneered with composite resin and subjected to fatigue tests. The fatigue limit was evaluated using the staircase method and the fatigue life of the samples was evaluated by subjecting the crowns to a load lower than the fatigue limit of that particular group, and also with an intermediate load of 522 N. A graphical plot was generated from the shape parameter (β) and life parameter (α) values obtained through the Weibull analysis method. Kruskal-Wallis and Mann-Whitney tests were applied to determine the significance differences in the recorded fracture mode between the study groups. The damage modes of the samples were assessed using Burke's classification.

RESULTS

The recorded fatigue limits of the groups were 442.8 ± 42.1 N, 608.7 ± 7.6 N, and 790.4 ± 29.2 N for zirconia, NiCr and PEKK, respectively. A significant difference in the fatigue limit of the groups was observed (p < 0.05). PEKK samples demonstrated the highest survival cycles of 1,170,000 and the lowest survival cycles was observed with zirconia samples at 100,000 under 522 N loading. The fracture modes in PEKK samples were largely distributed between code 1 and 2 whereas the fracture modes in NiCr group was distributed between code 1 and 4 and YZ crowns exhibited more of code 5 fractures. The difference in fracture modes among the groups was statistically significant (p < 0.05).

CONCLUSION

The PEKK group demonstrated better results compared to zirconia and NiCr based crowns. The PEKK group demonstrated high fatigue limit and survived the highest fatigue life cycles among the tested groups.

Adhesion to high-performance polymers applied in dentistry: A systematic review

OBJECTIVE

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).

METHODS

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.

RESULTS

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 26.72MPa (95% confidence interval (CI), 19.69-33.76; p<0.00001) and increased SBS by 4.86MPa (95% CI, 2.61-7.10; p<0.00001). Air abrasion improved SBS by 4.90MPa (95% CI, 3.90-5.90; p<0.00001) (50μm alumina) and 4.51MPa (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 33.76MPa (95% CI, 18.72-48.81; p<0.00001) and 33.28MPa (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.

SIGNIFICANCE

This review shows improved HPP bonding following the application of various surface pretreatments, including air abrasion and bonding agents.