title: [Effects of post length on the dislocation of post and core crown].
abstract: OBJECTIVE
  To evaluate the effects of the length of post on the dislocation of cast post and core crown.
  
  
  METHODS
  Forty simulated tooth roots made of polymethyl methacrylate were divided into five groups according to different length of post. These cast post and core were bonded with zinc phosphate cement. Then these specimens were strectched on the INSTRON-4302 by the speed of 10 mm/min. The maximum of load was recorded.
  
  
  RESULTS
  The loads of 7 mm, 7.5 mm, 8 mm, 8.5 mm, 9 mm were (203.25 +/- 57.19) N, (213.63 +/- 45.06) N, (234.44 +/- 59.27) N, (317.75 +/- 60.94) N, (334.25 +/- 58.00) N respectively. Linear regression analysis revealed the linear relationship of post length with dislocation, bonding, and mechanical interlocking; the values of r being 0.676, 1.000, 0.949; the regression equations being D = 73.225L - 325.776, B = 0.442L + 9.951, M = 72. 676L-334. 338.
  
  
  CONCLUSIONS
  Mechanical interlocking is the main factor in dislocation of post and core crown. The length of post should be increased from 2/3 to 3/4 of the length of tooth root when prepared in clinic.
authors.affiliation: Department of Prosthodontics, West China School of Stomatology, Sichuan University, Chengdu 610041, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Yang
authors.forename: Xin-Min
authors.initials: XM
authors.lastname: Chen
authors.forename: Xiao-Hong
authors.initials: XH
authors.lastname: Wu
authors.forename: Wei
authors.initials: W
authors.lastname: Yao
authors.forename: Lin
authors.initials: L
authors.lastname: Niu
mesh_terms: D003442:Crowns; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D006801:Humans; D011176:Post and Core Technique