Flexural behavior of PEEK materials for dental application

Highlights

  • Eleven PEEK compounds were evaluated by three-point bending tests.

  • The results of the bending strengths and bending moduli were measured.

  • The required minimum bending strength for dental plastics of 65 MPa was exceeded.

  • The lowest results were evaluated for an unfilled brand.

  • A PEEK compound reinforced by continuous carbon fibers showed the highest results.

Abstract

Objectives

The high-performance thermoplastic polymer PEEK (poly-ether-ether-ketone) is used as alternative implant material to metals since 1998 in many medical fields due to its bone-like mechanical properties. These iso-elastic characteristics of PEEK lead to the assumption, that it could represent a viable alternative to conventional materials also in the field of dentistry. Therefore the mechanical properties of different PEEK-compounds should be eavuated vie the three-point bending test.

Methods

150 specimens of 11 different PEEK-compounds were tested via a three-point bending test using a universal testing machine (Z010, Zwick GmbH & Co, Ulm, Germany) after dry storage on the one hand and after incubation at 37 °C in Ringer solution (Fa. Braun Melsungen AG, Melsungen, Deutschland) for one day, 7 days, 28 days und 84 days on the other hand and the material parameters bending modulus and bending strength were evaluated.

Results

The results regarding the bending moduli ranged from 2.73 ± 0.26 GPa for an unfilled brand to 47.27 ± 10.3 GPa for a carbon fiber reinforced PEEK with unidirectional continuous carbon fibers. Accordingly the bending strengths of these two material types ranged from 170.37 ± 19.31 MPa to 1009.63 ± 107.33 MPa.

Significance

All tested specimens showed higher values than the prevailing minimum strength for plastic materials and their application in dentistry of 65 MPa (DIN EN ISO 10477). This underlines the applicability of PEEK in dentistry and points out the possibility to offer patients metal free restorations, especially in the presence of allergies and/or bruxism.

Introduction

PEEK (poly-ether-ether-ketone) is well known as a high-performance thermoplastic polymer able to replace metallic components. Since April 1998, PEEK has also been commercially offered as implant material for long-term implantation (Invibio, Ltd., Thornton-Cleveleys, United Kingdom) . Due to its elastic modulus, similarly to that of cortical bone, it plays an important role as viable alternative to conventional implant materials such as titanium in the field of orthopedics and traumatology . Also in the field of dentistry, where traditionally a wide range of alloplastic materials is used, the application of PEEK increases replacing those conventional dental materials . This can be associated with distinct problems. Besides hypersensitivities against distinct components of dental composites on the one hand, even titanium, which is known as a proven biocompatible metal, has recently been suspected to provoke inflammatory reactions on the other hand . Additionally, more and more patients desire metal free reconstructions , to avoid the risk of oral galvanism for instance .

Due to its mechanical properties, which can be influenced by adding different compound materials such as carbon fibers (CFR-PEEK) , PEEK might represent a viable biomaterial, not only able to replace conventional polymers, but also even metals, alloys and ceramics in the field of dentistry.

The aim of this study was to evaluate the mechanical properties of different commercial PEEK compounds via three-point-bending tests, since the load distribution corresponds to a three-unit bridge in principle.

Materials and method

The materials (samples) examined are quoted in Table 1 .

Table 1
Summary of the different evaluated PEEK types.
Sample name Product name, manufacturer Compounds Production process Semi-finished product form Raw material biocompatibility tested according to ISO 10993-1 recommendations for For industrial application(industrial grade)
U 1 VESTAKEEP ® M4 R, Evonik Industries, Essen, Germany Extrusion Round rod, Ø 6 mm Permanent skin contact, prolonged mucosal membrance contact
U 2 PEEK-OPTIMA ® LT1, Invibio Ltd., Thornton Cleveleys, UK Extrusion Round rod, Ø 8 mm Permanent contact duration implant devices
Ti-10 PEEK-CLASSIX ® BC1-WH, Invibio Ltd., Thornton Cleveleys, UK 10% TiO 2 powder Extrusion Round rod, Ø 47 mm Prolonged contact implant devices
Ti-20 VESTAKEEP ® DC4420 R, Evonik Industries, Essen, Germany 20% TiO 2 powder Extrusion Round rod, Ø 6 mm Permanent mucosal membrance contact
Ba-6 PEEK-OPTIMA ® LT16BA, Invibio Ltd., Thornton Cleveleys, UK 6% BaSO 4 powder Extrusion Round rod, Ø 8 mm Permanent contact duration implant devices
Ba-20 PEEK-OPTIMA ® LT120BA, Invibio Ltd., Thornton Cleveleys, UK 20% BaSO 4 powder Extrusion Round rod, Ø 8 mm Permanent contact duration implant devices
G-30 VICTREX ® PEEK™ 450GL30, Victrex Ltd., Thornton Cleveleys, UK 30% multi-directional chopped glass fibers Injection molding Square plate, ≈100 × 100 × 10 mm X
C 1 -30 PEEK-OPTIMA ® LT1CA30, Invibio Ltd., Thornton Cleveleys, UK 30% multi-directional chopped carbon fibers Extrusion Square rod, 22 × 22 mm Permanent contact duration implant devices
C 2 -30 VICTREX ® PEEK™ 450CA30, Victrex Ltd., Thornton Cleveleys, UK 30% multi-directional chopped carbon fibers Injection molding Square plate, ≈100 × 100 × 10 mm X
C 1 -50 CF/PEEK, Icotec AG, Altstätten, Switzerland >50% multi-directional continuous carbon fibers; individual tantalum wires Pultrusion Round rod, Ø 5.5 mm Permanent contact duration implant devices
C 2 -50 PEEK-OPTIMA ® Ultra Reinforced, Invibio Ltd., Thornton Cleveleys, UK >50% uni-directional continuous carbon fibers Pultrusion Round rod, Ø 4 mm Permanent contact duration implant devices

Specimens in the shape of small bars were manufactured from the 11 PEEK-compounds by means of a diamond circular saw (Vari/Cut VC-50, Leco Corporation, St. Joseph, Michigan, USA), which was performed under continuous water cooling.

These specimens were 15 mm long at a ratio of width and height of 2:1. The manufactured small bars were supposed to be 2.0 to 2.5 mm in width, their height 1.0 to 1.5 mm.

All in all, 150 specimens were manufactured. In a number of n ≥ 5 they were tested after dry storage on the one hand and after incubation in Ringer solution (Braun Melsungen AG, Melsungen, Germany) at 37 °C on the other hand for one day ( t 1 ), 7 days ( t 2 ), 28 days ( t 3 ) and 84 days ( t 4 ).

The three-point-bending tests were performed using a universal testing machine (Z010, Zwick GmbH & Co, Ulm, Germany), in accordance to DIN EN ISO 178, 02/1997 (“Bending tests at synthetic materials”), at a feed speed of 1 mm/min.

In this procedure, the small bars were placed upon two supports, which were spaced at 10 mm from each other, while the small bars were exposed to the load of a wedge-shaped indenter with a curved edge of a cross section radius of 0.5 mm ( Fig. 1 ).

Fig. 1
Test set-up of the 3-point bending test.

Both the material parameters, flexural modulus and flexural strength were evaluated in the bending tests.

The statistical evaluation of these findings was performed using the OriginPro 7.5G SR2 program (OriginLab Corporation, Northampton, MA, USA).

The significance level for differences in the findings was at p < 0.05.

Materials and method

The materials (samples) examined are quoted in Table 1 .

Table 1
Summary of the different evaluated PEEK types.
Sample name Product name, manufacturer Compounds Production process Semi-finished product form Raw material biocompatibility tested according to ISO 10993-1 recommendations for For industrial application(industrial grade)
U 1 VESTAKEEP ® M4 R, Evonik Industries, Essen, Germany Extrusion Round rod, Ø 6 mm Permanent skin contact, prolonged mucosal membrance contact
U 2 PEEK-OPTIMA ® LT1, Invibio Ltd., Thornton Cleveleys, UK Extrusion Round rod, Ø 8 mm Permanent contact duration implant devices
Ti-10 PEEK-CLASSIX ® BC1-WH, Invibio Ltd., Thornton Cleveleys, UK 10% TiO 2 powder Extrusion Round rod, Ø 47 mm Prolonged contact implant devices
Ti-20 VESTAKEEP ® DC4420 R, Evonik Industries, Essen, Germany 20% TiO 2 powder Extrusion Round rod, Ø 6 mm Permanent mucosal membrance contact
Ba-6 PEEK-OPTIMA ® LT16BA, Invibio Ltd., Thornton Cleveleys, UK 6% BaSO 4 powder Extrusion Round rod, Ø 8 mm Permanent contact duration implant devices
Ba-20 PEEK-OPTIMA ® LT120BA, Invibio Ltd., Thornton Cleveleys, UK 20% BaSO 4 powder Extrusion Round rod, Ø 8 mm Permanent contact duration implant devices
G-30 VICTREX ® PEEK™ 450GL30, Victrex Ltd., Thornton Cleveleys, UK 30% multi-directional chopped glass fibers Injection molding Square plate, ≈100 × 100 × 10 mm X
C 1 -30 PEEK-OPTIMA ® LT1CA30, Invibio Ltd., Thornton Cleveleys, UK 30% multi-directional chopped carbon fibers Extrusion Square rod, 22 × 22 mm Permanent contact duration implant devices
C 2 -30 VICTREX ® PEEK™ 450CA30, Victrex Ltd., Thornton Cleveleys, UK 30% multi-directional chopped carbon fibers Injection molding Square plate, ≈100 × 100 × 10 mm X
C 1 -50 CF/PEEK, Icotec AG, Altstätten, Switzerland >50% multi-directional continuous carbon fibers; individual tantalum wires Pultrusion Round rod, Ø 5.5 mm Permanent contact duration implant devices
C 2 -50 PEEK-OPTIMA ® Ultra Reinforced, Invibio Ltd., Thornton Cleveleys, UK >50% uni-directional continuous carbon fibers Pultrusion Round rod, Ø 4 mm Permanent contact duration implant devices
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Nov 23, 2017 | Posted by in Dental Materials | Comments Off on Flexural behavior of PEEK materials for dental application
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