title: The effect of the disc support system on biaxial tensile strength of a glass ionomer cement.
abstract: OBJECTIVE
  This was to examine how varying the type of support, from a complete ring to a series of point supports, affected the biaxial tensile strength of one glass ionomer cement.
  
  
  METHODS
  Three support diameters from 11.5 to 28.6 mm were achieved using 3 mm ball bearings as point supports equidistantly spaced around the diameter. From 3-30 point supports were used depending on diameter. At the maximum number of point supports for each diameter the support points were 3 mm apart. After 24h storage in water at 37 degrees C the biaxial tensile strength of 1 mm thick glass ionomer restorative cement discs was measured using a loading rate of 1 mm min(-1). The load at break was converted to biaxial tensile strength using the Timoschenko and Woinowsky-Kreiger equation using a Poisson's ratio value of 0.30. The mean strength of six specimens tested per support regime was calculated.
  
  
  RESULTS
  Comparison with the mean result obtained from using a continuous knife-edge support showed there to be no significant difference (unpaired t-test) between the different support systems except in two cases, both being when a four-point support was used. Neither the support diameter nor the number of point supports was crucial.
  
  
  CONCLUSIONS
  Results from studies where different systems have been used to support brittle cement discs may be compared.
authors.affiliation: Department of Biomaterials, Eastman Dental Institute, London, UK. jwilliams@eastman.ucl.ac.uk
authors.forename: Jill A
authors.initials: JA
authors.lastname: Williams
authors.forename: Richard W
authors.initials: RW
authors.lastname: Billington
authors.forename: Gavin J
authors.initials: GJ
authors.lastname: Pearson
mesh_terms: D001840:Dental Bonding; D003799:Dental Stress Analysis; D005899:Glass Ionomer Cements; D008422:Materials Testing; D008433:Mathematics; D013718:Tensile Strength
chemical_list: D005899:Glass Ionomer Cements; C119823:HiFi cement