title: Erosion of water-based cements evaluated by volumetric and gravimetric methods.
abstract: OBJECTIVE
  To compare the erosion of glass ionomer, zinc phosphate and polycarboxylate cements using volumetric and gravimetric methods.
  
  
  METHODS
  For the volumetric method, the eroded depth of cement placed in a cylindrical cavity in PMMA was measured using a dial gauge after immersion in an eroding solution. For the gravimetric method, the weight of the residue of a solution in which a cylindrical specimen had been immersed was measured. 0.02 M lactic acid solution (0.02 M acid) and 0.1 M lactic acid/sodium lactate buffer solution (0.1 M buffer) were used as eroding solutions. The pH of both solutions was 2.74 and the test period was 24 h.
  
  
  RESULTS
  Ranking of eroded depth and weight of residue was polycarboxylate>zinc phosphate>glass ionomers. Differences in erosion were more clearly defined by differences in eroded depth than differences in weight of residue. In 0.02 M acid, the erosion of glass ionomer using the volumetric method was effected by the hygroscopic expansion. In 0.1 M buffer, the erosion for polycarboxylate and zinc phosphate using the volumetric method was much greater than that using the gravimetric method. This is explained by cryo-SEM images which show many holes in the surface of specimens after erosion. It appears that zinc oxide is dissolved leaving a spongy matrix which easily collapses under the force applied to the dial gauge during measurement.
  
  
  CONCLUSIONS
  The volumetric method that employs eroded depth of cement using a 0.1 M buffer solution is able to quantify erosion and to make material comparisons.
authors.affiliation: Department of Dental Engineering, Tsurumi University School of Dental Medicine, 2-1-3 Tsurumi, Tsurumi-Ku, 230-8501, Yokohama, Japan. nomoto-r@tsurumi-u.ac.jp
authors.forename: Rie
authors.initials: R
authors.lastname: Nomoto
authors.forename: Keiko
authors.initials: K
authors.lastname: Uchida
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Momoi
authors.forename: John F
authors.initials: JF
authors.lastname: McCabe
mesh_terms: D002021:Buffers; D003343:Corrosion; D003738:Dental Cements / Q000737:chemistry*; D005899:Glass Ionomer Cements / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007101:Immersion; D019344:Lactic Acid / Q000737:chemistry; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D011076:Polycarboxylate Cement / Q000737:chemistry; D019354:Sodium Lactate / Q000737:chemistry; D013499:Surface Properties; D014867:Water / Q000737:chemistry; D017155:Wettability; D015036:Zinc Phosphate Cement / Q000737:chemistry
chemical_list: D002021:Buffers; D003738:Dental Cements; D005899:Glass Ionomer Cements; D011076:Polycarboxylate Cement; D014867:Water; D019344:Lactic Acid; D015036:Zinc Phosphate Cement; D019354:Sodium Lactate