title: [Effect of investment composition ratio for pure titanium crown and bridge on some mechanical properties of mould].
abstract: OBJECTIVE
  To determine the optimal composition of a self-developing investment material by measuring physical and mechanical properties of mould.
  
  
  METHODS
  L(9) (3(4)) orthogonal design was adopted. One hundred and fifty specimens with the size of 80 mm × 20 mm × 20 mm were prepared to measure the atmospheric temperature bending strength, high temperature bending strength and residual bending strength. Nine specimens with the size of 5 mm diameter 25 mm heigh were prepared to survey the thermal expansion curve from ambient temperature to 1150°C.
  
  
  RESULTS
  Strengths were greatly affected by fine powder proportion in refractory and water/powder ratio. When the content of fine powder was 35% and water/powder ratio was 1:7.5, adequate atmospheric temperature strength and high temperature strength could be achieved. Moreover, the residual strength was moderate. The thermal extension curves of specimens in experiment group were almost similar. And the average linear expansion coefficient was (4 ∼ 5) × 10(-6)/°C.
  
  
  CONCLUSIONS
  The three kinds of bending strength of self-developing investment material are compared with commercialized investment material for titanium casting when water/powder ratio and the content of fine powder are carefully controlled.
authors.affiliation: Dental Institute, General Hospital of PLA, Beijing 100853, China. yangyangfeifei@yahoo.com.cn
authors.forename: Se-fei
authors.initials: SF
authors.lastname: Yang
authors.forename: You-xu
authors.initials: YX
authors.lastname: Wang
authors.forename: Tian-wen
authors.initials: TW
authors.lastname: Guo
authors.forename: Hong-chen
authors.initials: HC
authors.lastname: Liu
mesh_terms: D003442:Crowns; D003734:Dental Casting Investment; D003735:Dental Casting Technique; D003799:Dental Stress Analysis; D006358:Hot Temperature; D008422:Materials Testing; D018583:Pliability; D011208:Powders; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: D003734:Dental Casting Investment; D011208:Powders; D014025:Titanium