Comparison of the fracture strength of different materials used for cantilever prosthesis

Sönmez, E. (2024). Comparison of the fracture strength of different materials used for cantilever prosthesis. Yeditepe University, Institute of Health Sciences, PhD thesis, Istanbul. Purpose: The aim of this study is to compare the fracture strength of fixed prosthetic frameworks made from PEEK, PEKK, and PMMA polymers, in comparison to infrastructures made from Zirconia, in a simulated the oral environment. Materials and Methods: To simulate the clinical scenario of an edentulous posterior region in vitro, two implants with a center-to-center distance of 15 mm were embedded in acrylic resin. Frameworks were milled from CAD/CAM blocks in four different materials—PEEK, PEKK, PMMA, and Zirconia—each with two cantilever lengths: 10 mm (1 molar) and 20 mm (2 molars). After milling, all samples underwent thermocycling with the following program: 20,000 cycles in two water baths (5°C and 55°C). Each cycle lasted 60 seconds: 20 seconds in each bath and 10 seconds for each transfer between the baths. The prepared samples were cemented with resin-modified glass ionomer cement and tested under a vertical force applied 2 mm from distal end of cantilever. The force was applied at a speed of 1 mm/min using an Instron Universal Testing Machine 3228. Values for deformation and decementation have been documented. Normality of the parameters was evaluated using Kolmogorov-Smirnov and Shapiro-Wilks tests. Data was analyzed with two-way analysis of variance (ANOVA). Results: There was statistically significant difference in decementation and deformation values both according to cantilever lengths and among the materials (p:0.001 ; p<0.05). The Zirconia group demonstrated the highest decementation load values at both cantilever lengths(10 mm samples 338±24 N, 20 mm samples 141±167 N ). The mean deformation maximum load values for a 10 mm Zirconia sample were 642±102 N, significantly exceeding the corresponding values for PEEK (417±53 N), PEKK (360±59 N), and PMMA (344±97 N). Similarly, for the 20 mm samples, Zirconia (248±26 N) also showed higher values compared to PEEK (126±9 N), PEKK (124±10 N), and PMMA (173±24 N). Conclusions: For all materials used, the mean maximum deformation load at 10 mm length was statistically significantly higher than at 20 mm length. Zirconia exhibited the highest fracture strength and decementation load values at both 10 mm and 20 mm cantilever lengths. Keywords: PEEK, PEKKTON, cantilever, fracture strength.