title: Failure behavior of glass ionomer cement under Hertzian indentation.
abstract: OBJECTIVE
  To investigate the load-bearing capacity and failure mode of various types of glass ionomer cement (GIC) under Hertzian indentation, exploring the relationship between the failure behavior and formulation, and examining claims of filler-reinforcement of GIC.
  
  
  METHODS
  Discs 2mm thick, 10mm diameter, 8-18 replicates, were fabricated for two filler-reinforced GICs, four unmodified and unreinforced GICs, and four resin-modified GICs, with a dental silver amalgam and a filled-resin restorative material for comparison. Testing was at 23 degrees C, wet, after 7d storage at 37 degrees C in artificial saliva at pH 6, using a 20mm diameter hard steel ball and filled-nylon substrate (E: 10GPa). First failure was detected acoustically; mode was determined visually. At least 1/3 of specimens in each case were examined under scanning electronic microscope for corroboration.
  
  
  RESULTS
  Reinforced and unmodified-unreinforced GICs were indistinguishable by failure load (one-way analysis of variance, P=0.425, overall 260+/-70N) and mode. Failure loads for resin-modified GICs were 360-1150N, amalgam approximately 680N, and filled resin approximately 1200N. Resin-modified GICs tended to be tougher (incomplete fracture), all others gave complete fracture (radial cracking). The stronger materials (two resin-modified GICs and filled resin) showed some cone cracking.
  
  
  CONCLUSIONS
  While resin-modified GICs showed various extents of increase of failure load over that of the plain GICs, consistent with the hybrid chemistry, filler-reinforcement was not evident for the two claimed products, consistent with structural and theoretical expectations.
authors: Department of Prosthodontics, Guanghua School of Stomatology, Sun Yat-sen University, Guang Zhou, China.
authors: Yan
authors: Y
authors: Wang
authors: B W
authors: BW
authors: Darvell
mesh_terms: D000162:Acoustics; D016722:Cermet Cements / Q000737:chemistry; D020770:Compomers / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D003723:Dental Amalgam / Q000737:chemistry; D005899:Glass Ionomer Cements / Q000737:chemistry*; D006244:Hardness; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D009757:Nylons / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D012464:Saliva, Artificial / Q000737:chemistry; D012834:Silver / Q000737:chemistry; D013232:Steel / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D016722:Cermet Cements; D020770:Compomers; D003188:Composite Resins; D005899:Glass Ionomer Cements; D009757:Nylons; D019279:Resin Cements; D012464:Saliva, Artificial; D014867:Water; D013232:Steel; D012834:Silver; D003723:Dental Amalgam