title: Effect of unilateral misfit on preload of retention screws of implant-supported prostheses submitted to mechanical cycling.
abstract: OBJECTIVE
  The aim of this study was to evaluate the effect of different levels of unilateral angular misfit on preload maintenance of retention screws of single implant-supported prostheses submitted to mechanical cycling.
  
  
  METHODS
  Premachined UCLA abutments were cast with cobalt-chromium alloy to obtain 48 crowns divided into four groups (n=12). The crowns presented no misfit in Group A (control group) and unilateral misfits of 50 μm, 100 μm and 200 μm in the groups B, C and D, respectively. The crowns were attached to external hexagon implants with a titanium retention screw with torque of 30 N/cm. Oblique loading of 130 N at 2 Hz was applied on each replica, totalizing 5×10⁴ and 1×10⁶ cycles. Detorque values were measured initially and after each cycling period. Data were evaluated by analysis of variance and Tukey's HSD test (p<0.05).
  
  
  RESULTS
  All groups presented reduced initial detorque values (p<0.05) in comparison to the insertion torque (30±0.5 N/cm) and Group A (25.18 N/cm) exhibited the lowest reduction. After mechanical cycling, all groups presented detorque values from 19.5 N/cm to 22.38 N/cm and the mechanical cycling did not statistically influence the detorque values regardless the misfit level of the replicas.
  
  
  CONCLUSIONS
  The unilateral misfit influenced the preload maintenance only before mechanical cycling. The mechanical cycling did not influence the torque reduction.
authors.affiliation: Department of Dental Materials and Prosthodontics, Araçatuba Dental School, Univ Estadual Paulista (UNESP), José Bonifácio, 1193, São Paulo 16015-050, Brazil. wirley@foa.unesp.br
authors.forename: Wirley Gonçalves
authors.initials: WG
authors.lastname: Assunção
authors.forename: Valentim Adelino Ricardo
authors.initials: VA
authors.lastname: Barão
authors.forename: Juliana Aparecida
authors.initials: JA
authors.lastname: Delben
authors.forename: Érica Alves
authors.initials: ÉA
authors.lastname: Gomes
authors.forename: Idelmo Rangel
authors.initials: IR
authors.lastname: Garcia
mesh_terms: D002858:Chromium Alloys; D003442:Crowns; D000044:Dental Abutments; D003722:Dental Alloys; D017267:Dental Prosthesis Design; D017268:Dental Prosthesis Retention / Q000379:methods*; D019094:Dental Prosthesis, Implant-Supported; D003799:Dental Stress Analysis; D017755:Prosthesis Fitting; D013314:Stress, Mechanical; D019415:Torque
chemical_list: D002858:Chromium Alloys; D003722:Dental Alloys