title: A quality assessment of the casting process on magnetic keepers.
abstract: OBJECTIVE
  The objective of this study was to qualitatively investigate the effect of the burn-out (mold) temperature, investment material, and casting alloy on the surface integrity of the Magfit EX keeper.
  
  
  METHODS
  Forty-two Magfit EX keepers were waxed-up, invested in five investment materials (Beauty-Cast, Cristobalite, CM-10, Cera-Fina, Castorit-super), and subjected to burn-out temperatures ranging from 450 to 700 degrees C at intervals of 50 degrees C. The keeper samples were then cast into copings with three alloys (Castwell, Protor 3, Optimum) under standard conditions. The keeper surfaces were then examined under a microscope, and the compositions were assessed by an X-ray micro-analyzer in a scanning electron microscope (SEM). A new keeper served as control.
  
  
  RESULTS
  At a burn-out temperature of 550 degrees C, the keeper surface started to disintegrate. X-ray micro-analysis showed an increase in oxygen content with increasing temperature. At 700 degrees C, the keeper surface disintegrated, and the composition differed markedly from that of the new keeper. The keeper surfaces were intact with all investments except those with Beauty-Cast. The keeper surfaces were found to be damaged when the casting alloy was Optimum.
  
  
  CONCLUSIONS
  Beauty-Cast investment with a burn-out temperature of 700 degrees C is unsuitable for casting the Magfit EX keeper-coping unit. Also, high fusing alloys are not recommended for casting Magfit EX keepers.
authors: Faculty of Dentistry, The University of Hong Kong, China.
authors: Henry W K
authors: HW
authors: Luk
authors: Edmond H N
authors: EH
authors: Pow
authors: Andrew P L H
authors: AP
authors: Dias
mesh_terms: D002133:Calcium Sulfate / Q000737:chemistry; D003722:Dental Alloys / Q000737:chemistry; D003734:Dental Casting Investment / Q000737:chemistry; D003735:Dental Casting Technique / Q000295:instrumentation / Q000592:standards*; D003781:Denture Retention / Q000295:instrumentation* / Q000592:standards; D004577:Electron Probe Microanalysis; D006358:Hot Temperature; D006801:Humans; D008280:Magnetics / Q000295:instrumentation*; D008422:Materials Testing; D008853:Microscopy; D008855:Microscopy, Electron, Scanning; D010100:Oxygen / Q000032:analysis; D012822:Silicon Dioxide / Q000737:chemistry; D013499:Surface Properties; D013696:Temperature
chemical_list: D003722:Dental Alloys; D003734:Dental Casting Investment; C118503:cerafina; D012822:Silicon Dioxide; D010100:Oxygen; D002133:Calcium Sulfate