title: The influence of screw type, alloy and cylinder position on the marginal fit of implant frameworks before and after laser welding.
abstract: Misfit at the abutment-prosthetic cylinder interface can cause loss of preload, leading to loosening or fracture of gold and titanium screws.
  
  
  OBJECTIVE
  To evaluate the influence of screw type, alloy, and cylinder position on marginal fit of implant frameworks before and after laser welding.
  
  
  METHODS
  After Estheticone-like abutments were screwed to the implants, thirty plastic prosthetic cylinders were mounted and waxed-up to fifteen cylindrical bars. Each specimen had three interconnected prosthetic components. Five specimens were one-piece cast in titanium and five in cobalt-chromium alloy. On each specimen, tests were conducted with hexagonal titanium and slotted gold screws separately, performing a total of thirty tested screws. Measurements at the interfaces were performed using an optical microscope with 5mm accuracy. After sectioning, specimens were laser welded and new measurements were obtained. Data were submitted to a four-way ANOVA and Tukey's multiple comparisons test (alpha=0.05).
  
  
  RESULTS
  Slotted and hexagonal screws did not present significant differences regarding to the fit of cylinders cast in titanium, either in one-piece casting framework or after laser welding. When slotted and hexagonal screws were tested on the cobalt-chromium specimens, statistically significant differences were found for the one-piece casting condition, with the slotted screws presenting better fit (24.13 microm) than the hexagonal screws (27.93 microm). Besides, no statistically significant differences were found after laser welding.
  
  
  CONCLUSIONS
  1) The use of different metal alloys do exert influence on the marginal fit, 2) The slotted and hexagonal screws play the exclusive role of fixing the prosthesis, and did not improve the fit of cylinders, and 3) cylinder position did not affect marginal fit values.
authors.affiliation: Department of Dental Materials, Bauru Dental School, University of São Paulo, Brazil.
authors.forename: Daniela
authors.initials: D
authors.lastname: Castilio
authors.forename: Ana Paula Ribeiro do Vale
authors.initials: AP
authors.lastname: Pedreira
authors.forename: Paulo Henrique Orlato
authors.initials: PH
authors.lastname: Rossetti
authors.forename: Leylha Maria Nunes
authors.initials: LM
authors.lastname: Rossetti
authors.forename: Wellington Cardoso
authors.initials: WC
authors.lastname: Bonachela