Abrasion resistance of PEEK, CAD/CAM composite and PMMA

Effects of the test specimen geometry, the antagonist materials and the test setup

Authors: Anja Liebermann, Annett Kieschnick, Bogna Stawarczyk

PEEK, CAD/CAM composites and CAD/CAM-PMMA are increasingly being used in digital dentistry. But how do the materials behave in the mouth in the long term? In the study presented here, these materials were tested with regard to various aspects.

Several studies tested the performance of CAD/CAM plastic restorations in terms of their color stability and mechanical properties [1-4]. Comparable or even better results have been achieved than with glass ceramics [1-4]. A major advantage of plastics over ceramics is the lower modulus of elasticity, which enables functional loads to be dampened [4]. Another advantage is the higher abrasion resistance compared to the enamel antagonist [4, 5, 6].

When it comes to plastics, the focus at the moment is also on polyetheretherketone (PEEK) – a polymer from the main group PAEK (Polyaryletherketone). PEEK is available as an industrially produced blank/block for CAD/CAM production or as pellets or granules for pressing technology. Due to its excellent physical and biological properties, PEEK has gained wide acceptance in medicine and has been proposed as a potential material for definitive dental prosthesis [7,8]. With regard to the bond between PEEK and other dental plastics, the initial difficulties have been overcome; the results are promising [1, 8, 9-18]. However, there is limited data on the wear behavior of CAD/CAM plastics - especially PEEK. In view of this, an already published study is presented below.

Details of the study

the aim of the study

were examined

the 2-body wear of three CAD/CAM plastics as well
the influence of the test specimen geometry, the antagonist material and the test setup on the result.

Study structure

The following plastics were tested:

thermoplastic PEEK (Dentokeep, nt-trading),
experimental CAD/CAM nanohybrid composite (Ivoclar Vivadent)
PMMA-based CAD/CAM material (artBloc Temp, Merz Dental)

Plane test specimen clamped in a chewing simulator for artificial aging

Crown-shaped and flat test specimens were made from each of these materials and subjected to aging against human tooth enamel and stainless steel antagonists using thermomechanical loading in a chewing simulator (50 N, 5/55 °C, 600.000 chewing cycles). Half of the test specimens in each group were loaded with a sliding movement of 0,7 mm and the other half were axially loaded. The wear of the materials and the antagonists was evaluated using a Match 3D method and the topography of all surfaces was then examined using scanning electron microscopy (SEM).

Results of the study

When subjected to lateral loading, the PEEK material showed significantly lower material loss than the composite or the PMMA plastic. Within the axially loaded groups, this only applied to the flat test specimens tested with enamel antagonists. The test setup with crowns showed lower loss rates than the test setup with flat test pieces. Above all, the lateral movement led to significantly higher material losses than the axial load. On the antagonist side, no influence of the CAD/CAM material, the antagonist material, the application of force and the test specimen geometry could be determined.

3D image of an abraded surface (crown) after chewing simulation

Conclusion

The wear of PEEK was generally lower than that of composite and PMMA-based materials under lateral loading. The test setup and the load on the test specimens played an important role. Planar test specimens loaded with lateral movement lead to higher material losses. The practitioner must take these aspects into account when evaluating the studies.

Study: Wimmer T, Huffmann AM, Eichberger M, Schmidlin PR, Stawarczyk B. Two-body wear rate of PEEK, CAD/CAM resin composite and PMMA: Effect of specimen geometries, antagonist materials and test set-up configuration. Dent Mater. 2016;32(6):e127-36.

Authors' summary

The abrasion behavior - material as well as antagonist - is particularly clinically relevant for the selection of the appropriate restorative material. Dentists and dental technicians should be sufficiently informed about this. To date, there are hardly any long-term clinical studies on CAD/CAM plastics or PEEK.

further reading

1. Stawarczyk B, Ender A, Trottmann A, Özcan M, Fischer J, Hämmerle CH. Load-bearing capacity of CAD/CAM milled polymeric three-unit fixed dental prostheses: effect of aging regimens. Clin Oral Investig 2012;16:1669-77.
2. Fischer J, Roeske S, Stawarczyk B, Hämmerle CH. Investigations in the correlation between Martens hardness and flexural strength of composite resin restorative materials. Dent Mater J 2010;29:188-92.
3. Stawarczyk B, Sener B, Trottmann A, Roos M, Özcan M, Hämmerle CH. Discoloration of manually fabricated resins and industrially fabricated CAD/CAM blocks versus glass-ceramic: effect of storage media, duration, and subsequent polishing. Dent Mater J 2012;31:377-83.
4. Carvalho AO, Bruzi G, Giannini M, Magne P. Fatigue resistance of CAD/CAM complete crowns with a simplified cementation process. J Prosthet Dent 2014;111:310-7.
5. Stawarczyk B, Özcan M, Trottmann A, Dirt F, Roos M, Hämmerle C. Two-body wear rate of CAD/CAM resin blocks and their enamel antagonists. J Prosthet Dent 2013;109:325-32.
6. Kunzelmann KH, Jelen B, Mehl A, Hickel R. Wear evaluation of MZ100 compared to ceramic CAD/CAM materials. Int J Comput Dent 2001;4:171-84.
7. Kurtz SM and Devine JN. PEEK biomaterials in trauma, orthopedic, and spinal implants. Biomaterials 2007;28:4845-4869.
8. Stawarczyk B, Beuer F, Wimmer T, Jahn D, Sener B, Roos M and Schmidlin PR. Polyetheretherketone-a suitable material for fixed dental prostheses? J Biomed Mater Res B Appl Biomater 2013;101:1209-1216.
9. Uhrenbacher J, Schmidlin PR, Keul C, Eichberger M, Roos M, Gernet W, Stawarczyk B. The effect of surface modification on the retention strength of polyetheretherketone crowns adhesively bonded to dentin abutments. J Prosthet Dent 2014;112:1489-97.
10. Stawarczyk B, Jordan P, Schmidlin PR, Roos M, Eichberger M, Gernet W, Keul C. PEEK surface treatment effects on tensile bond strength to veneering resins. J Prosthet Dent 2014;112:1278-88.
11. Stawarczyk B, Keul C, Beuer F, Roos M, Schmidlin PR. Tensile bond strength of veneering resins to PEEK: influence of different adhesives. Dent Mater J 2013;32:441-8.
12. Schmidlin PR, Stawarczyk B, Wieland M, Attin T, Hämmerle CH, Fischer J. Effect of different surface pre-treatments and luting materials on shear bond strength to PEEK. Dent Mater 2010;26:553-9.
13. Kern M, Lehmann F. Influence of surface conditioning on bonding to polyetheretherketone (PEEK). Dent Mater. 2012;28(12):1280-1283.
14. Fuhrmann G, Steiner M, Freitag-Wolf S, Kern M. Resin bonding to three types of polyaryl ether ketones (PAEKs)-durability and influence of surface conditioning. Dent Mater 2014;30:357-63.
15. Stawarczyk B, Bahr N, Beuer F, Wimmer T, Eichberger M, Gernet W, Jahn D, Schmidlin PR. Influence of plasma pretreatment on shear bond strength of self-adhesive resin cements to polyetheretherketone. Clin Oral Investig 2014;18:163-70.
16. Rosentritt M, Preis V, Behr M, Sereno N, Kolbeck C. Shear bond strength between veneering composite and PEEK after different surface modifications. Clin Oral Investig 2015;19:739-44.
17. Hallmann L, Mehl A, Sereno N, Hämmerle CHF. The improvement of adhesive properties of PEEK through different pre-treatments. Appl Surf Sci 2012;258:7213-8.
18. Sproesser O, Schmidlin PR, Uhrenbacher J, Eichberger M, Roos M and Stawarczyk B. Work of adhesion between resin composite cements and PEEK as a function of etching duration with sulfuric acid and its correlation with bond strength values. Int J Adhes Adhes 2014;54:184-90.

Abrasion resistance of PEEK, CAD/CAM composite and CAD/CAM-PMMA

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