title: Removal Torque and Biofilm Accumulation at Two Dental Implant-Abutment Joints After Fatigue.
abstract: OBJECTIVE
  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.
  
  
  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 (FN) 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/cm²) 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 μm) and external hexagon (21.1 ± 0.7 μm) abutments after fatigue tests than those recorded without fatigue tests (respectively, 24 ± 0.5 μm and 24.8 ± 0.6 μm) 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 μm) than those recorded after fatigue tests (3.2 ± 0.8 μm). Also, mean values of microgap size for external hexagon joints free of fatigue were statistically signicantly lower (1.5 ± 0.4 μm) than those recorded after fatigue tests (8.1 ± 1.7 μm) (P < .05). The optical density of biofilms and CFU mean values were lower on Morse taper abutments (Abs630nm at 0.06 and 2.9 × 10⁴ CFU/cm²) than that on external hexagon abutments (Abs630nm at 0.08 and 4.5 × 10⁴ CFU/cm²) (P = .01).
  
  
  CONCLUSIONS
  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.
authors.forename: Jorge
authors.initials: J
authors.lastname: Pereira
authors.forename: Carolina S
authors.initials: CS
authors.lastname: Morsch
authors.forename: Bruno
authors.initials: B
authors.lastname: Henriques
authors.forename: Rubens M
authors.initials: RM
authors.lastname: Nascimento
authors.forename: Cesar Am
authors.initials: CA
authors.lastname: Benfatti
authors.forename: Filipe S
authors.initials: FS
authors.lastname: Silva
authors.forename: José
authors.initials: J
authors.lastname: López-López
authors.forename: Júlio Cm
authors.initials: JC
authors.lastname: Souza
mesh_terms: D000704:Analysis of Variance; D018441:Biofilms / Q000254:growth & development*; D015169:Colony Count, Microbial; D000044:Dental Abutments / Q000382:microbiology*; D059605:Dental Implant-Abutment Design; D015921:Dental Implants / Q000382:microbiology*; D019094:Dental Prosthesis, Implant-Supported / Q000382:microbiology*; D003799:Dental Stress Analysis; D006801:Humans; D013499:Surface Properties; D019415:Torque
chemical_list: D015921:Dental Implants