Torque loss and Biofilm penetration at dental implant joints after fatigue tests

Objectives: Evaluate the detorque and in vitro biofilm penetration at Morse Tapper and Hexagonal dental implant joints after fatigue tests.
Methods: Sixty dental implants (Neodent® implants, Curitiba, Brazil) were divided into two groups: Morse taper; and external hexagon abutment-implant systems. Fatigue tests on the implant-abutment assemblies were performed at a normal force (FN) of 50 N, at 1.2 Hz for 500000 cycles in growth medium containing human saliva, for 72h and then the detorque mean values were measured (n=10). The abutments were immersed in protease 1% solution in order to detach the biofilms for optical density and CFU/ml analyses. Groups of implant-abutment assemblies (n= 8) were cross-sectioned at 90° relative to the plane of the abutment-implant joints for the microgap measurement by Field-Emission Guns Scanning Electron Microscopy.
Results: A significant statistically decrease of torque loss mean values was noticed on external hexagon or Morse taper abutments after fatigue tests in biofilm medium for 72 h (p < 0,05). There was an increase of microgap sizes at both joints after fatigue tests, having higher size measurements at external hexagon joints (1.5 ± 0.4 μm before and 8,1 ± 1,7 μm after fatigue tests) than those at Morse taper ones (1.7 ± 0.4 μm before and 3.2 ± 0.8 μm after). Mean values on biofilm density and viable colony-forming unit were lower on Morse taper abutments than that on external hexagon abutments.
Conclusions: The mean values of detorque, microgap size and biofilm density recorded at Morse taper were lower in comparison to those recorded at external hexagon abutment-implant joints after fatigue tests in a simulated oral environment for 72 h.