The thermoplastic polyetheretherketone, or PEEK for short, has interesting special features for prosthetic restorations. On the one hand, the material is biocompatible because it is monomer-free. In addition, due to its low density, PEEK is very light and has sufficient stability to serve as a framework material or substructure for complex restorations. As is so often the case, in-depth knowledge of material properties helps dental technicians to reduce any problems or rule them out from the outset. Basically, the dental processing processes must be adapted to the properties of PEEK. PEEK is one of the very opaque materials and has a white, brownish or beige color. This means that PEEK restorations have to be veneered in the visible area. The materials science team at the Polyclinic for Dental Prosthetics at the LMU Munich conducted an investigation into the veneering of PEEK frameworks. The following abstract describes the experimental setup and the conclusion.
The aim of this study was to examine the breaking load of three-unit, differently veneered PEEK bridges. A PEEK filled to 20% with inorganic agents (titanium oxide) was used as the framework material.
For this purpose, a three-unit bridge 23-24-25 was constructed fully anatomically on a CAD/CAM system using a master model and then reduced to a congruent shape in the area of the veneer. The area to be veneered should have an even thickness of veneer. From the master STL data set created in this way, a total of 120 congruent bridge frameworks were milled out of a PEEK blank. These bridges were randomly divided into four groups (N = 120, n = 30 per veneering group) and veneered with four different veneering technologies.
Image from the experimental setup. Three-member PEEK bridges from a master data set
- Group I = Digital veneering (breCAM.HIPC)
- Group II = Conventional veneering with a low-viscosity veneering composite (crea.lign)
- Group III = Conventional veneering with a highly viscous veneering composite (crea.lign paste)
- Group IV = veneering with prefabricated veneers (visio.lign)
The veneer was always manufactured exactly according to the manufacturer's instructions. After veneering, the bridges were adhesively attached to the master model, which was made of a non-precious metal (NEM). The breaking load could now be tested in a universal testing machine from Zwick at a feed rate of 1 mm/min before and after aging in thermal load cycles (10.000 thermal cycles, 5/55 °C). Thermal load aging simulates the thermal stress on materials that occurs in vivo when eating and drinking cold (e.g. ice cream) and hot (e.g. coffee or soup) foods. The data obtained was then statistically evaluated.
Result
A significant influence of the veneering technique on the breaking load of the veneered PEEK bridges could be observed. The highest breaking loads were measured for bridges with the digital veneer (1882 ± 152 N without aging, 2021 ± 184 N after thermocycling). For the other bridges, the breaking load values (1008-1229 N) were significantly lower. No significant effect of thermal aging was observed in any of the tested groups. The fracture pattern analysis showed cracks in the veneer in the area of the pontic in the groups of conventionally veneered bridges and in the group of digital veneers. In the bridges that were veneered using veneers, the shells were found to be detached.
In summary, it can be said that digital veneering leads to the highest overall stability of the PEEK frameworks. There was no noticeable difference in stability between the manufacturer-made veneers and the manual composite veneers. Thermal aging had no influence on the breaking load of all PEEK bridges tested.
Clinical Relevance
According to these study results, digital veneering of three-unit PEEK bridges resulted in the most reliable breaking load values. The breaking load values of PEEK frameworks veneered conventionally or with veneers are also significantly higher than the average chewing force of around 600 N.
Author: Bogna Stawarczyk, Annett Kieschnick (www.annettkieschnick.de)
Overdenture in the upper jaw based on a PEEK framework. The veneering was carried out using ready-made veneers. (Images: ZTM P. von der Osten)
A wax fitting fitted in the mouth is digitized and the veneer is milled from a high-performance polymer using CAD/CAM. (Images: ZTM P. von der Osten)
From analog to digital: The framework with wax fitting (left) and the milled veneer (right). (Image: ZTM P. von der Osten)
The restoration placed in the mouth. The digitally manufactured veneer was slightly customized with composite in the area 13 to 23. (Image: ZTM P. von der Osten)
FURTHER INFORMATION ON THE PRESENTED INVESTIGATION
Full article published in: Clin Oral Investig. 2016 Mar 15. [Epub ahead of print] Fracture load and failure types of different veneered polyetheretherketone fixed dental prostheses. Taufall S, Eichberger M, Schmidlin PR, Stawarczyk B.