title: Influence of Diamondlike Carbon Coating of Screws on Axial Tightening Force and Stress Distribution on Overdenture Bar Frameworks with Different Fit Levels and Materials.
abstract: OBJECTIVE
  The aim of this study was to evaluate the axial tightening force applied by conventional and diamondlike carbon (DLC)-coated screws and to verify, through three-dimensional finite element analysis (FEA), the stress distribution caused by different framework materials and prosthetic screws in overdenture frameworks with different misfit levels.
  
  
  METHODS
  The axial tightening force applied by the screw was evaluated by means of a titanium matrix connected to a load cell. Conventional titanium or DLC-coated screws were tightened with a digital torque wrench, and the load values were recorded. The values were applied in an FEA to a bar-clip attachment system connected to two 4.0 × 11-mm external-hexagon titanium implants placed in an anterior edentulous arch. DLC-coated and conventional screws were modeled with their respective axial forces obtained on the experimental evaluation for three bar framework materials (titanium, nickel-chromium, and cobalt-chromium) and three levels of misfit (100, 150, and 200 μm). Von Mises stresses for prosthetic components and maximum principal stress and microstrains (maximum principal strains) for bone tissue were measured.
  
  
  RESULTS
  The mean force applied by the conventional screw was 25.55 N (± 1.78); the prosthetic screw coated with a DLC layer applied a mean force of 31.44 N (± 2.11), a statistically significant difference. In the FEA, the DLC screw led to higher stresses on the framework; however, the prosthetic screw suffered lower stress. No influence of screw type was seen in the bone tissue.
  
  
  CONCLUSIONS
  Titanium frameworks reduced the stress transmitted to the bone tissue and the bar framework but had no influence on the screws. Higher misfit values resulted in an increased stress/strain in bone tissue and bar framework, which was not the case for retention screws.
authors.forename: Mateus Bertolini Fernandes
authors.initials: MB
authors.lastname: dos Santos
authors.forename: Atais
authors.initials: A
authors.lastname: Bacchi
authors.forename: Rafael Leonardo Xediek
authors.initials: RL
authors.lastname: Consani
authors.forename: Lourenço
authors.initials: L
authors.lastname: Correr-Sobrinho
mesh_terms: D002244:Carbon / Q000737:chemistry*; D002858:Chromium Alloys / Q000737:chemistry; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D015921:Dental Implants; D018772:Dental Marginal Adaptation; D003764:Dental Materials / Q000737:chemistry; D019094:Dental Prosthesis, Implant-Supported; D003779:Denture Design; D003781:Denture Retention / Q000295:instrumentation*; D003828:Denture, Overlay; D018130:Diamond / Q000737:chemistry; D020342:Finite Element Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008334:Mandible / Q000502:physiology; D008422:Materials Testing; D013314:Stress, Mechanical; D014025:Titanium / Q000737:chemistry; D019415:Torque
chemical_list: D002858:Chromium Alloys; D020099:Coated Materials, Biocompatible; D015921:Dental Implants; D003764:Dental Materials; D002244:Carbon; D018130:Diamond; D014025:Titanium