title: Screw joint stability after the application of retorque in implant-supported dentures under simulated masticatory conditions.
abstract: BACKGROUND
  Screws can loosen through mechanisms that have not been clearly established.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the influence of the tightening technique (the application of torque and retorque on the joint stability of titanium and gold prosthetic screws) in implant-supported dentures under different fit levels after 1 year of simulated masticatory function by means of mechanical cycling.
  
  
  METHODS
  Ten mandibular implant-supported dentures were fabricated, and 20 cast models were prepared by using the dentures to create 2 fit levels: passive fit and created misfit. The tightening protocol was evaluated according to 4 distinct profiles: without retorque plus titanium screws, without retorque plus gold screws, retorque plus titanium screws, and retorque plus gold screws. In the retorque application, the screws were tightened to 10 Ncm and retightened to 10 Ncm after 10 minutes. The screw joint stability after 1 year of simulated clinical function was measured with a digital torque meter. Data were analyzed statistically by 2-way ANOVA and Tukey honestly significant difference (HSD) post hoc tests (α=.05).
  
  
  RESULTS
  The factors of fit level and tightening technique as well as the interaction between the factors, were statistically significant. The misfit decreases the loosening torque. The retorque application increased joint stability independent of fit level or screw material, which suggests that this procedure should be performed routinely during the tightening of these devices.
  
  
  CONCLUSIONS
  All tightening techniques revealed reduced loosening torque values that were significantly lower in misfit dentures than in passive fit dentures. However, the retorque application significantly increased the loosening torque when titanium and gold screws were used. Therefore, this procedure should be performed routinely during screw tightening.
authors.affiliation: Department of Restorative Dentistry, Passo Fundo Dental School, University of Passo Fundo, Passo Fundo, RS, Brazil. Electronic address: ana_goergen@yahoo.com.br.
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Farina
authors.affiliation: Departments of Dental Materials, Piracicaba Dental School, State University of Campinas, Piracicaba, SP, Brazil.
authors.forename: Aloísio Oro
authors.initials: AO
authors.lastname: Spazzin
authors.affiliation: Department of Prosthodontics and Periodontology, Piracicaba Dental School, State University of Campinas, Piracicaba, SP, Brazil.
authors.forename: Rafael Leonardo Xediek
authors.initials: RL
authors.lastname: Consani
authors.affiliation: Department of Prosthodontics and Periodontology, Piracicaba Dental School, State University of Campinas, Piracicaba, SP, Brazil.
authors.forename: Marcelo Ferraz
authors.initials: MF
authors.lastname: Mesquita
mesh_terms: D059605:Dental Implant-Abutment Design / Q000295:instrumentation*; D015921:Dental Implants; D018772:Dental Marginal Adaptation; D003764:Dental Materials / Q000737:chemistry; D017268:Dental Prosthesis Retention / Q000295:instrumentation*; D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D008409:Mastication / Q000502:physiology*; D012464:Saliva, Artificial / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D019415:Torque
chemical_list: D015921:Dental Implants; D003764:Dental Materials; D006047:Gold Alloys; D012464:Saliva, Artificial; D014025:Titanium