title: Axial displacement of external and internal implant-abutment connection evaluated by linear mixed model analysis.
abstract: OBJECTIVE
  To analyze the axial displacement of external and internal implant-abutment connection after cyclic loading.
  
  
  METHODS
  Three groups of external abutments (Ext group), an internal tapered one-piece-type abutment (Int-1 group), and an internal tapered two-piece-type abutment (Int-2 group) were prepared. Cyclic loading was applied to implant-abutment assemblies at 150 N with a frequency of 3 Hz. The amount of axial displacement, the Periotest values (PTVs), and the removal torque values(RTVs) were measured. Both a repeated measures analysis of variance and pattern analysis based on the linear mixed model were used for statistical analysis. Scanning electron microscopy (SEM) was used to evaluate the surface of the implant-abutment connection.
  
  
  RESULTS
  The mean axial displacements after 1,000,000 cycles were 0.6 μm in the Ext group, 3.7 μm in the Int-1 group, and 9.0 μm in the Int-2 group. Pattern analysis revealed a breakpoint at 171 cycles. The Ext group showed no declining pattern, and the Int-1 group showed no declining pattern after the breakpoint (171 cycles). However, the Int-2 group experienced continuous axial displacement. After cyclic loading, the PTV decreased in the Int-2 group, and the RTV decreased in all groups. SEM imaging revealed surface wear in all groups.
  
  
  CONCLUSIONS
  Axial displacement and surface wear occurred in all groups. The PTVs remained stable, but the RTVs decreased after cyclic loading. Based on linear mixed model analysis, the Ext and Int-1 groups' axial displacements plateaued after little cyclic loading. The Int-2 group's rate of axial displacement slowed after 100,000 cycles.
authors.forename: Hyon-Woo
authors.initials: HW
authors.lastname: Seol
authors.forename: Seong-Joo
authors.initials: SJ
authors.lastname: Heo
authors.forename: Jai-Young
authors.initials: JY
authors.lastname: Koak
authors.forename: Seong-Kyun
authors.initials: SK
authors.lastname: Kim
authors.forename: Shin-Koo
authors.initials: SK
authors.lastname: Kim
mesh_terms: D000465:Algorithms; D001732:Bite Force; D059605:Dental Implant-Abutment Design; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D016014:Linear Models; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D013314:Stress, Mechanical; D013499:Surface Properties; D019415:Torque