title: Improving the fit of implant prosthetics: an in vitro study.
abstract: OBJECTIVE
  Accurate and passive fit between a prosthesis and its supporting implants has been considered a prerequisite for successful long-term osseointegration. The objective of this in vitro study was to evaluate the strain development during tightening of a five-unit screw-retained superstructure constructed using five different methods.
  
  
  METHODS
  Five-unit screw-retained fixed partial prostheses (n = 25) were fabricated on three implants embedded in an epoxy resin block using five different methods: (1) cobalt-chromium (Co-Cr), plastic cylinders, one-piece cast; (2) Co-Cr, plastic cylinders, framework sectioned, preceramic laser-welding soldering; (3) gold-platinum (Au-Pt), gold cylinders, one-piece cast; (4) Au-Pt, gold cylinders, framework sectioned, preceramic laser-welding soldering; (5) Co-Cr, one-piece cast, and cementation to "passive abutments" (Southern Implants) after final finishing and polishing. Strain gauges (SG) were attached to the fixed partial prosthesis (FPP) and to the resin block to measure the stress created during screw tightening.
  
  
  RESULTS
  The combination of Co-Cr alloy and plastic cylinders in a one-piece cast showed such an inadequate fit among the fabricated methods that this group was excluded from the remainder of the experiment. Specimens of Au-Pt cast on gold cylinders in one piece showed higher strain development than the other groups used in this study, with strains ranging from 223.1 to 2,198.1 Μm/m. Sectioning and soldering significantly improved the overall fit. FPPs of Co-Cr in a one-piece cast cemented to "passive abutments" produced the best level of fit, with the least strain development in the prosthesis and the resin block (59 to 204.6 Μm/m).
  
  
  CONCLUSIONS
  Absolute fit of superstructures on implants is not possible using conventional laboratory procedures. Cementing FPPs onto prefabricated cylinders directly onto the implants significantly reduces strain development compared to the other fabrication methods.
authors: Department of Dental Technology, Division of Removable Prosthodontics, Technological Educational Institution of Athens, Athens, Greece. yannista@otenet.gr
authors: Stavros
authors: S
authors: Yannikakis
authors: Anthony
authors: A
authors: Prombonas
mesh_terms: D002484:Cementation; D002858:Chromium Alloys; D059605:Dental Implant-Abutment Design / Q000592:standards; D017267:Dental Prosthesis Design / Q000379:methods; D017268:Dental Prosthesis Retention / Q000379:methods* / Q000592:standards; D019094:Dental Prosthesis, Implant-Supported / Q000295:instrumentation / Q000592:standards*; D019232:Dental Restoration Failure; D003830:Denture, Partial, Fixed / Q000592:standards*; D006047:Gold Alloys; D006801:Humans; D010984:Platinum; D013314:Stress, Mechanical
chemical_list: D002858:Chromium Alloys; D006047:Gold Alloys; D010984:Platinum