title: In vitro mechanical analysis of complete-arch mandibular implant-supported fixed prostheses abutment screws after cyclic loading.
abstract: BACKGROUND
  Clinicians question when to evaluate for worn or loose implant-supported retainer screws to prevent possible clinical complications.
  
  
  OBJECTIVE
  The purpose of this study was to compare differences among initial and postdynamically loaded detorque values and identify physical structural changes of prosthetic retaining screws in a simulated implant-supported mandibular complete fixed prosthesis.
  
  
  METHODS
  Nine groups and nonloaded controls comprising a 5-implant-supported, milled titanium framework were fabricated and assembled (screw torque 35 Ncm). Dynamic loading (20 to 220 N) was applied to simulate 2 years of oral function. After testing, screw detorque values were measured (ΔT, initial-detorque value). A scanning electron microscopic analysis of screw threads was used to assess physical changes. Data were analyzed by 2-way ANOVA to determine the influence of loading and implant position on ΔT (α=.05).
  
  
  RESULTS
  ΔT values of loaded and nonloaded groups were compared separately at each implant position and showed a significant difference only for the implant in the central position (P=.002). All positions were compared in terms of ΔT values separately for loaded and nonloaded conditions. A significantly higher ΔT was found in 1 cantilever area of the loaded group, whereas a significantly lower ΔT value was found in the central position in the nonloaded group. No statistically significant differences were found in physical changes between loading and nonloading or among implant positions.
  
  
  CONCLUSIONS
  When delivering a multiimplant supported prosthesis, the application of dynamic loading and the sequence in which implant screws are tightened could influence the subsequent detorque value of a screw; they have no effect on the physical appearance of screws after extended function.
authors: Assistant Professor, Department of Oral Rehabilitation, Georgia Regents University, College of Dental Medicine, Augusta, Ga.
authors: Andreina
authors: A
authors: Sananez
authors: Dean, College of Dental Medicine, Georgia Regents University, Augusta, Ga.
authors: Carol
authors: C
authors: Lefebvre
authors: Professor, Department of Biostatistics and Epidemiology, Georgia Regents University, College of Dental Medicine, Augusta, Ga.
authors: Stephen
authors: S
authors: Looney
authors: Program Director, Advanced Education in Prosthodontics Program, Georgia Regents University, College of Dental Medicine, Augusta, Ga.
authors: Philip
authors: P
authors: Baker
authors: Dental research equipment technician, Dental Materials Section, Department of Oral Rehabilitation, Georgia Regents University, College of Dental Medicine, Augusta, Ga.
authors: Don
authors: D
authors: Mettenburg
authors: Professor and Section Director, Dental Materials Section, Department of Oral Rehabilitation, Georgia Regents University, College of Dental Medicine, Augusta, Ga. Electronic address: frueggeb@gru.edu.
authors: Frederick A
authors: FA
authors: Rueggeberg
mesh_terms: D001696:Biomechanical Phenomena; D001732:Bite Force; D003198:Computer Simulation; D000044:Dental Abutments; D015921:Dental Implants; D003764:Dental Materials / Q000737:chemistry; D019094:Dental Prosthesis, Implant-Supported; D003826:Denture, Complete, Lower; D006801:Humans; D008334:Mandible / Q000502:physiology; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D008954:Models, Biological; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D014025:Titanium / Q000737:chemistry; D019415:Torque
chemical_list: D015921:Dental Implants; D003764:Dental Materials; D014025:Titanium