Fracture Strength of Zirconia Implants after Artificial Aging

Zirconia (ZrO2) might be an alternative material to titanium (Ti) for dental implant fabrication. However, no data are available on the fracture strength of one-piece ZrO2 oral implants. The objective of this study was to evaluate the fracture strength of ZrO2 implants after exposure to the artificial mouth. One hundred twenty ZrO2 and Ti implants were used. The Ti implants were divided into two control groups (A and B). ZrO2 implants manufactured from yttria-stabilized tetragonal ZrO2 polycrystal (Y-TZP) in group C, from Y-TZP dotted with alumina (Y-TZP-A) in group D, and from Y-TZP-A with a modified surface in groups E and F were used. In group F, the implant heads were prepared, and in group G, the implants were restored with ZrO2 crowns. Each group included 16 samples with the exception of group D, which included 24 samples. A subgroup of each implant type (eight implants) was subjected to thermomechanical cycling in a chewing simulator prior to fracture testing. Test specimens were then loaded until a fracture occurred. Seven of the 120 samples failed in the chewing simulator. ZrO2 implant fracture occurred at 725 to 850 N when the implants were not prepared, and at 539 to 607 N when prepared. The samples in group A fractured at the level of the abutment screw. All ZrO2 implants fractured at the level of the Technovit (R) resin (Heraeus Kulzer GmbH & Co., Wehrheim, Germany). No fracture of the ZrO2 crowns in group G was observed. Mean fracture strength values obtained were all within the limits of clinical acceptance. However, implant preparation had a statistically significant negative influence on the implant fracture strength. Long-term clinical data are necessary before one-piece ZrO2 implants can be recommended for daily practice.