title: Optimal specimen geometry in bonded-disk shrinkage-strain measurements on light-cured biomaterials.
abstract: OBJECTIVE
  The aim was to determine the effect on apparent shrinkage-strain values of varying specimen aspect ratio in the bonded-disk configuration. Thereby one source of possible inter-laboratory variation might be understood and eliminated.
  
  
  METHODS
  The bonded-disk procedure was followed and applied to three representative resin-composites. However, specimen sub-groups were examined, each of different diameters (3.5, 5.0, 7.0 and 9.0 mm), corresponding to C-factors in the range 0.45-7.0.
  
  
  RESULTS
  For each material, no statistically significant difference was apparent between data obtained with 7 and 9 mm diameter specimens. However, statistically significant reductions (p < 0.05, Scheffé and SNK) were apparent at 5.0 and 3.5 mm diameter, in the range 14-18% of the maximum 'true' value. For each material, the diameter (d)-dependence of apparent shrinkage-strain (epsilon) was given by the curve fit expression: epsilon = A - B/d2.
  
  
  CONCLUSIONS
  For accurate determination of maximum final equilibrium shrinkage-strain values, a high aspect ratio (7-9:1) of the bonded-disk should be utilised. This is important for accurate comparison of data from proposed low-shrinkage amalgam-replacement materials.
authors.affiliation: University of Manchester Dental School, Higher Cambridge Street, Manchester M15 6FH, UK. david.watts@man.ac.uk
authors.forename: D C
authors.initials: DC
authors.lastname: Watts
authors.forename: A S
authors.initials: AS
authors.lastname: Marouf
mesh_terms: D000704:Analysis of Variance; D002627:Chemistry, Physical / Q000379:methods; D003188:Composite Resins / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000379:methods*; D008027:Light; D008422:Materials Testing / Q000379:methods; D011108:Polymers / Q000737:chemistry; D015203:Reproducibility of Results; D018709:Statistics, Nonparametric; D013674:Technology, Dental / Q000379:methods*
chemical_list: D003188:Composite Resins; D011108:Polymers