Wear investigation of implant-supported upper removable prothesis with electroplated gold or PEKK secondary crowns

The aim of the present study was to investigate, whether polyetherketoneketone (PEKK) secondary crowns could be considered as alternative to gold standard in terms of their physical properties and manufacturing costs.

An upper jaw model with six implants was used. Frameworks with either 6 PEKK- or 6 electroplated secondary crowns were cemented in a wear simulator. A total of 20 specimens (10 PEKK, 10 gold) run 10,000 cycles in the wear simulator with a lubricant. Additionally, 10,000 cycles in the thermocycling baths with 5 °C and 55 °C have gone through, before running extra 10,000 cycles in the wear simulator again. Finally, the abutments were analysed for signs of wear under the electron microscope.

The mean pulling out force value for PEKK was 21 N. For the electroplated gold secondary crowns an average of 19 N was measured. Multiple fluctuations were observed in the gold series of tests. After 20,000 cycles in the wear simulator and 10,000 cycles in the thermocycling machine, there were no major losses to be measured in terms of wear for both materials. In the microscopic analysis of the abutments, traces of wear could be seen in pull-out direction, mainly in the gold samples.

PEKK secondary crowns have lower costs, more stable retention force values and are easier to produce than the gold standard. On average, the pull-out force values were 11 N higher than recommended.