title: The effect of mechanical cycling and different misfit levels on Vicker's microhardness of retention screws for single implant-supported prostheses.
abstract: OBJECTIVE
  The aim of this study was to evaluate the effect of mechanical cycling and different misfit levels on Vicker's microhardness of retention screws for single implant-supported prostheses.
  
  
  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 groups B, C, and D, respectively. The crowns were screwed to external hexagon implants with titanium retention screws (torque of 30 N/cm), and the sets were submitted to three different periods of mechanical cycling: 2×10(4) , 5×10(4) , and 1×10(6) cycles. Screw microhardness values were measured before and after each cycling period. Data were evaluated by two-way ANOVA and Tukey's test (p < 0.05).
  
  
  RESULTS
  Mechanical cycling statistically reduced microhardness values of retention screws regardless of cycling periods and groups. In groups A, B, and C, initial microhardness values were statistically different from final microhardness values (p < 0.05). There was no statistically significant difference for initial screw microhardness values (p > 0.05) among the groups; however, when the groups were compared after mechanical cycling, a statistically significant difference was observed between groups B and D (p < 0.05).
  
  
  CONCLUSIONS
  Mechanical cycling reduced the Vicker's microhardness values of the retention screws of all groups. The crowns with the highest misfit level presented the highest Vicker's microhardness values.
authors: Department of Dental Materials and Prosthodontics, Araçatuba Dental School, Univ Estadual Paulista (UNESP), Sao Paulo, Brazil.
authors: Wirley Gonçalves
authors: WG
authors: Assunção
authors: Juliana Ribeiro Pala
authors: JR
authors: Jorge
authors: Paulo Henrique
authors: PH
authors: Dos Santos
authors: Valentim Adelino
authors: VA
authors: Barão
authors: Erica Alves
authors: EA
authors: Gomes
authors: Juliana Aparecida
authors: JA
authors: Delben
mesh_terms: D000704:Analysis of Variance; D003442:Crowns; D019250:Dental Implants, Single-Tooth; D017268:Dental Prosthesis Retention / Q000295:instrumentation*; D019094:Dental Prosthesis, Implant-Supported; D003799:Dental Stress Analysis; D006244:Hardness; D006245:Hardness Tests; D006801:Humans; D008422:Materials Testing; D017755:Prosthesis Fitting; D014025:Titanium
chemical_list: D014025:Titanium