title: Fracture toughness of resin-modified glass ionomer restorative materials: effect of powder/liquid ratio and powder particle size reduction on fracture toughness.
abstract: OBJECTIVE
  The objectives of the current investigation were two-fold: (1) to examine the effect of different powder/liquid (P/L) ratios on the fracture toughness of commercial resin-modified glass ionomer cement and conventional glass ionomer cement, and (2) to evaluate the effect of powder size reduction on the fracture toughness of experimental resin-modified glass ionomers in order to improve their physical properties.
  
  
  METHODS
  The P/L ratios of the glass ionomer and resin-modified glass ionomers were varied from the manufacturer's recommended ratio to 2.0 and 1.0 by weight. The powder particle sizes for the experimental resin-modified glass ionomers tested were 2, 5, 10 and 25 micro m in diameter. Fracture toughness was determined on ring-shaped specimens with a fatigued pre-crack.
  
  
  RESULTS
  The fracture toughness of the resin-modified glass ionomers was significantly higher (p<0.005) than that of the glass ionomer and was not greatly influenced by the P/L ratio. For the experimental resin-modified glass ionomers, it was observed that fracture toughness gradually decreased as the powder particle size became finer.
  
  
  CONCLUSIONS
  The resin components in the liquid play an important role in the improvement of the physical properties of the resin-modified glass ionomer. A reduction in the powder particle size of up to 10 micro m, which resulted in a smoother surface, can maintain high fracture toughness. The high fracture toughness values of the resin-modified glass ionomer may be one of the factors contributing to a favorable clinical outcome in high stress-bearing areas.
mesh_terms: D000704:Analysis of Variance; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003188:Composite Resins / Q000737:chemistry; D003793:Dental Restoration, Permanent; D005899:Glass Ionomer Cements / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D010316:Particle Size; D011208:Powders; D019279:Resin Cements / Q000737:chemistry*; D012117:Resins, Synthetic / Q000737:chemistry; D012996:Solutions; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength
chemical_list: D003188:Composite Resins; C079765:Fuji II LC cement; D005899:Glass Ionomer Cements; D011208:Powders; D019279:Resin Cements; D012117:Resins, Synthetic; D012996:Solutions; C084550:Vitremer; C084541:Fuji glass-ionomer lining cement