Load-bearing capacity of artificially aged zirconia fixed dental prostheses with heterogeneous abutment supports

Aim of this in vitro study was to investigate the effect of artificial ageing and differential abutment support on the load-bearing capacity of zirconia posterior four-unit fixed dental prostheses (FDPs). Thirty-six FDPs were fabricated using CAD/CAM technology and divided into three groups. Specimens in the first group were cemented onto tooth analogues with simulated periodontal resilience, in the second group onto a dental implant and a tooth analogue, but in the third group only onto implants. Half of the samples in each group underwent artificial ageing. Afterwards, all FDPs were loaded until bulk fracture in a universal testing machine. Load-displacement curves and forces at fracture were recorded and results were statistically analysed using ANOVA. Load-bearing capacities within the different test groups averaged as follows (control/artificially aged): tooth-tooth supported (2,009/1,751 N), tooth-implant supported (2,144/1,935 N) and implant-implant supported (2,689/2,484 N). Artificial ageing as well as differential abutment support did have a significant influence on the fracture strength of the zirconia FDPs. Implant-retained prostheses demonstrated the highest load-bearing capacity, while resilient support was demonstrated to be unfavourable. According to these in vitro results, zirconia four-unit prostheses may be promising for application in posterior areas with all three support scenarios (implant-assisted, tooth-retained, or implant-tooth-interconnected prostheses). However, the restorations' mechanical strength may expected to be significantly influenced in situ by ageing of the material on the long term.