Removal Torque and Biofilm Accumulation at Two Dental Implant-Abutment Joints After Fatigue

Purpose: The aim of this study was to evaluate the removal torque and in vitro biofilm penetration at Morse taper and hexagonal implant-abutment joints after fatigue tests. Materials and Methods: Sixty dental implants were divided into two groups: (1) Morse taper and (2) external hexagon implant-abutment systems. Fatigue tests on the implant-abutment assemblies were performed at a normal force (F-N) of 50 N at 1.2 Hz for 500,000 cycles in growth medium containing human saliva for 72 hours. Removal torque mean values (n = 10) were measured after fatigue tests. Abutments were then immersed in 1% protease solution in order to detach the biofilms for optical density and colony-forming unit (CFU/cm(2)) analyses. Groups of implant-abutment assemblies (n = 8) were cross-sectioned at 90 degrees relative to the plane of the implant-abutment joints for the microgap measurement by field-emission guns scanning electron microscopy. Results: Mean values of removal torque on abutments were significantly lower for both Morse taper (22.1 +/- 0.5 mu m) and external hexagon (21.1 +/- 0.7 mu m) abutments after fatigue tests than those recorded without fatigue tests (respectively, 24 perpendicular to 0.5 mu m and 24.8 perpendicular to 0.6 mu m) in biofilm medium for 72 hours (P = .04). Mean values of microgap size for the Morse taper joints were statistically signicantly lower without fatigue tests (1.7 +/- 0.4 mu m) than those recorded after fatigue tests (3.2 +/- 0.8 mu m). Also, mean values of microgap size for external hexagon joints free of fatigue were statistically signicantly lower (1.5 +/- 0.4 mu m) than those recorded after fatigue tests (8.1 +/- 1.7 mu m) (P < .05). The optical density of biofilms and CFU mean values were lower on Morse taper abutments (Abs(630nm) at 0.06 and 2.9 x 10(4) CFU/cm(2)) than that on external hexagon abutments (Abs(630nm) at 0.08 and 4.5 x 10(4) CFU/cm(2)) (P = .01). Conclusion: The mean values of removal torque, microgap size, and biofilm density recorded at Morse taper joints were lower in comparison to those recorded at external hexagon implant-abutment joints after fatigue tests in a simulated oral environment for 72 hours.