title: An in vitro comparison of joint stability of implant-supported fixed prosthetic suprastructures retained with different prosthetic screws and levels of fit under masticatory simulation conditions.
abstract: OBJECTIVE
  This study sought to determine an optimal postinsertion retorque protocol to maintain implantsuprastructure joint stability after being subjected to a 1-year in vitro masticatory simulation.
  
  
  METHODS
  Ten mandibular implant-supported dentures were manufactured and 20 epoxy resin models were obtained for two fit levels: passive fit and misfit. Eight groups (n = 20) were created on the basis of vertical fit (passive or misfit) and prosthetic screw material (titanium or gold). The single-screw test was performed and the vertical misfit was quantified using an optical microscope. Loosening torque was measured after simulations of two types of clinical use: (1) 6 months of use, torque loosening, retightening, another 6 months of use, and loosening torque; and (2) 1 year of use followed by loosening torque. Data were analyzed by means of two-way analysis of variance and the Tukey test.
  
  
  RESULTS
  The factors of cycling time and condition use (fit level and screw type), as well the interaction between these factors, significantly influenced the loosening torque (P < .05). After 6 months and another 6 months of clinical use simulation, titanium screws showed higher loosening torque values than did gold screws for the same fit level (P < .05). After 1 year of clinical use simulation, titanium and gold screws in passively fit dentures showed higher loosening torque values than they did in misfit dentures (P < .05). The titanium screws presented a decrease in the loosening torque after 1 year in misfit dentures.
  
  
  CONCLUSIONS
  The stability of titanium screws was higher than that of gold screws after 6 months of simulation because of their lower plastic deformation. When the cycling time was analyzed, titanium screws were less stable after 1 year of simulation because of loss of torque in the presence of misfit.
authors: Department of Prosthodontics and Periodontics, Piracicaba Dental School, Campinas State University, São Paulo, Brazil. ana_goergen@yahoo.com.br
authors: Ana Paula
authors: AP
authors: Farina
authors: Aloísio Oro
authors: AO
authors: Spazzin
authors: Juliana Maria Costa Nuñez
authors: JM
authors: Pantoja
authors: Rafael Leonardo Xediek
authors: RL
authors: Consani
authors: Marcelo Ferraz
authors: MF
authors: Mesquita
mesh_terms: D000704:Analysis of Variance; D001863:Bone Screws; D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000379:methods*; D006046:Gold; D008334:Mandible; D008409:Mastication; D013997:Time Factors; D014025:Titanium; D019415:Torque
chemical_list: D006046:Gold; D014025:Titanium