Objective: The clear biological advantages of ZrO2 implants maybe confronted by lower stability in the interface area. Therefore, the mechanical stability of two-piece ZrO2 implants should be tested and compared with that of titanium implants.
Material and method: The technically mature dynamic rotary oscillating loading method (DIN 1331-2) has already been tested in dentistry. Different types of ZrO2 implants (two-piece designs with different interface levels, cemented and screw-retained abutments with ZrO2 and titanium screws, and one-piece implants) were subjected to pseudo-realistic loads of 15 Ncm and 50 Ncm in a life-time mode. Before, during and after the stress tests, the loosening of the connection screw, the tilting and rotational freedom, and the fracture strength in the connecting area between the fixture and the abutment were determined.
Results: Fractures in the interface area occurred in 3% of cases at 15 Ncm loading and in 26% of cases at 50 Ncm. In particular, implants with cemented abutments and so-called bone level implants with ZrO2 screws were susceptible to fracture. The release torques of the abutment screws generally showed a high loss. The residual torque amounted to 64% of the initial tightening torque for titanium and only 36% for ZrO2. Increased torsional freedom up to 2.5° and more was observed for bone level implants with ZrO2 screws. For all implants, the tilting freedom was relatively stable, largely independent of the material and cementation of the connection screws. Considering all test criteria, superior stability of the connection between fixture and abutment was found for tissue level implants with titanium screws.
Summary: The dynamic rotary oscillating loading method can be used to simulate long-term loading of implants within a short period of time. Compared to titanium implants, ZrO2 implants showed largely better results regarding fracture strength, wear and loosening effects of the junction between fixture and abutment.
Keywords: Zirconium dioxide implants, mechanical stability, dynamic rotary oscillating loading test
