title: Effect of mixing method on the porosity of encapsulated glass ionomer cement.
abstract: OBJECTIVE
  To observe cement specimens mixed by various methods non-destructively using microfocus computerized tomography (micro-CT) and to evaluate the effect of mixing method on porosity.
  
  
  METHODS
  Five glass ionomer cements were used: two were hand-mixed and three were encapsulated. The latter were mixed either by shaking or rotating. Fifteen cylindrical specimens were prepared for each material by each mixing method and stored in distilled water at 37 degrees C until testing. The specimens were observed and analyzed using micro-CT. 201 sliced images were obtained horizontally along the length of the specimens. Three-dimensional reconstructions were made and the sizes, numbers and total volume ratio of bubbles in the specimens were calculated.
  
  
  RESULTS
  Mixing method had a significant effect on porosity (P<0.05). For the luting/lining cement, mechanical mixing produced a significantly higher porosity (P<0.05). For the restorative cement, there were only small differences in porosity between specimens mixed by the two methods. More large bubbles were detected in specimens mixed mechanically than by hand for the fluid material. This suggested that for low-viscosity materials bubbles may combine until a certain viscosity is reached during setting.
  
  
  CONCLUSIONS
  The strength of glass ionomer cement is affected by incorporated porosity and this depends on the mixing method. For low-viscosity cements, hand-mixing is favored in order to reduce porosity and increase strength, but this is not generally applicable to high-viscosity cements.
authors.affiliation: Department of Dental Engineering, Tsurumi University School of Dental Medicine 2-1-3 Tsurumi, Tsurumi-ku Yokohama, 230-8501 Japan.
authors.forename: Rie
authors.initials: R
authors.lastname: Nomoto
authors.forename: Manabu
authors.initials: M
authors.lastname: Komoriyama
authors.forename: John F
authors.initials: JF
authors.lastname: McCabe
authors.forename: Susumu
authors.initials: S
authors.lastname: Hirano
mesh_terms: D002484:Cementation; D019245:Compressive Strength; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis; D004339:Drug Compounding; D005899:Glass Ionomer Cements / Q000138:chemical synthesis / Q000737:chemistry; D008277:Magnesium Oxide / Q000138:chemical synthesis; D008422:Materials Testing; D011076:Polycarboxylate Cement / Q000138:chemical synthesis; D016062:Porosity; D014057:Tomography, X-Ray Computed; D014783:Viscosity; D015034:Zinc Oxide / Q000138:chemical synthesis
chemical_list: D005899:Glass Ionomer Cements; D011076:Polycarboxylate Cement; C110712:ketac-molar; D008277:Magnesium Oxide; C040235:Ketac-cem; D015034:Zinc Oxide