title: Screw preloads and measurements of surface roughness in screw joints: an in vitro study on implant frameworks.
abstract: BACKGROUND
  With the development of milled titanium implant frameworks, new surfaces that have not previously been studied are now being used in screw joints.
  
  
  OBJECTIVE
  The aims of the present study were to compare the preload produced in screw-retained titanium and gold alloy frameworks and the preload for titanium frameworks before and after the application of veneers. Another aim was to try to relate the surface roughness of the screw joints to variations in preload.
  
  
  METHODS
  Ten identical titanium and five gold alloy frameworks were fabricated. The gold screws were tightened to 10 Ncm. Preload measurements were made for the gold alloy frameworks and before and after the porcelain or acrylic resin veneers had been applied to the titanium frameworks. Surface roughness measurements were made after preload measurements on the screw joint surfaces of the titanium frameworks and corresponding gold screws.
  
  
  RESULTS
  The preloads for the titanium and gold alloy frameworks were similar. Preload in both types of frameworks decreased after repeated torques (p<.05-.01) but was unaffected by the application of veneering materials to the titanium frameworks (p>.05). No relationship (p>.05) between preload and surface roughness characteristics was observed. Loaded titanium framework screw sites, however, had lower mean S(a) values than unloaded sites (p<.001), whereas the surfaces of loaded gold screws had higher mean S(a) values compared with the surfaces of control gold screws (p<.05-.001).
  
  
  CONCLUSIONS
  When using gold screws, milled titanium frameworks have preloads similar to those of gold alloy frameworks and preloads for both decrease after repeated tightening. The preload was similar before and after the veneering of the titanium frameworks. Unloaded milled titanium screw sites had rougher surfaces than loaded, and loaded gold screws had rougher surfaces than unloaded. However, no correlation between screw joint surface and preload was observed for veneered titanium frameworks.
authors.affiliation: Consultant in prosthodontics, The Brånemark Clinic, Göteborg, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Ortorp
authors.forename: Torsten
authors.initials: T
authors.lastname: Jemt
authors.forename: Ann
authors.initials: A
authors.lastname: Wennerberg
authors.forename: Carina
authors.initials: C
authors.lastname: Berggren
authors.forename: Mattias
authors.initials: M
authors.lastname: Brycke
mesh_terms: D017076:Computer-Aided Design; D000044:Dental Abutments; D003722:Dental Alloys; D003758:Dental Implantation, Endosseous; D015921:Dental Implants; D017267:Dental Prosthesis Design; D017268:Dental Prosthesis Retention / Q000295:instrumentation*; D019094:Dental Prosthesis, Implant-Supported; D003799:Dental Stress Analysis; D003801:Dental Veneers; D006047:Gold Alloys; D018709:Statistics, Nonparametric; D013499:Surface Properties; D014025:Titanium; D019415:Torque
chemical_list: D003722:Dental Alloys; D015921:Dental Implants; D006047:Gold Alloys; D014025:Titanium