Comparative in vitro study on biomechanical behavior of zirconia and polyetheretherketone biomaterials exposed to experimental loading conditions in a prototypal simulator

Abstract

Zirconia and polyetheretherketone (PEEK) are two biomaterials widely investigated as substitute for metals in oral prosthetic rehabilitation. To achieve a proper biomechanical behavior, the prosthetic biomaterials must ensure a good resistance to loads, as this is a crucial characteristic enabling their use in dental applications. The aim of this study was to investigate differences in the fracture resistance of different biomaterials in an experimental environment: fixed partial dentures (FPDs) screwed in a prototype of biomimetic mandible. 10 Samples of FPDs were allocated in 2 groups (A and B): Group A (n=5) involved FPDs in zirconia-ceramic, and Group B (n=5) involved FPDs in PEEK-composite. The samples were loaded by means of a three-point bending mechanical test, and the load to fracture has been evaluated generating a point-by-point graphics (speed/load and time/deformation). The samples were further analyzed by micro-computed tomography (micro-CT) and described under experimental loading conditions. Zirconia-ceramic FDPs were the samples reporting the worst results, showing a lower value of vertical displacement with respect to PEEK-based samples. The micro-CT results have further confirmed the preliminary results previously described. This in vitro study aims to give analytic data on the reliability of PEEK as a reliable and strong biomaterial for prosthetic treatments.

Keywords: FPDs; PEEK; Zirconia; biomaterials; three-point bending test.

Figure 1

Two different perspectives of mandibular section simulator with two implants screwed inside: frontal view (a) and sagittal view (b).

Figure 2

Section of sample with reinforced fiber.

Figure 3

CAD project of frameworks: different wall thicknesses were designed for each CAD-CAM (Computer-Aided Design-Computer Aided Manufacturing) model.

Figure 4

Samples with zirconia framework and ceramic rich in leucite veneer.

Figure 5

Samples with PEEK framework and resin composite veneering.

Figure 6

Sample fitted in a vise and with strain gauge connected. (Distance a-0.6 cm/ distance b-2 cm).

Figure 7

Sample during three-point bending test: load was applied at the exact center of the structure. The three-point-bending test was performed using a universal testing machine (Instron 5566®, UK) at a feed speed of 1 mm/min.

Figure 8

Load-displacement graphics of five zirconia specimens: the figure shows the vertical displacement of zirconia-ceramic FDPs related to the applied loads. In the graphics, x-coordinate data are related to speed (mm/min), while y-coordinate are related to load (N).

Figure 9

Load-displacement graphics of five PEEK specimens: the figure shows the vertical displacement of PEEK-composite FDPs related to the applied loads. In the graphics, x-coordinate data are related to speed (mm/min), while y-coordinate are related to load (N).

Figure 10

Five zirconia-ceramic samples strain gauge graphics. The figure shows strain gauge graphics obtained to strain gauge machine. In the graphics, x-coordinate data are related to time (s), while y-coordinate data are related to deformation E.

Figure 11

Five PEEK- composite samples strain gauge graphics. The figure shows strain gauge graphics obtained to strain gauge machine. In the graphics, x-coordinate data are related to time (s), while y-coordinate data are related to deformation E. The variability between the results shown in the graph 10 and 11 is due to heterogeneity between the samples. The load has been the same to all the samples investigated; nevertheless, the manual finishing of samples has affected the homogeneity of the samples. Moreover, although a silicone mold has been used to homogenize the samples, unfortunately, the same silicon mold was another technical reason of the structural defects.

Figure 12

Micro-CT analysis of zirconia-ceramic specimens. The samples were analyzed with a micro-computed cone-beam x ray system and were scanned at magnification of 15 X. The figure shows different sections of specimens: occlusal section (a) and sagittal sections (b, c, d)

Figure 13

Micro-CT analysis of PEEK-composite specimens. The samples were analyzed with a micro-computed cone-beam x ray system and were scanned at magnification of 15 X. The figure shows different sections of specimens: occlusal section (b, c) and sagittal sections (a, d)