title: Effect of water on the physical properties of resin-modified glass ionomer cements.
abstract: OBJECTIVE
  Resin-modified glass ionomer cements (GIC) are available for clinical use as restorative materials or as liners and bases. This work was conducted to study the effect of water sorption on the physical properties of several resin-modified GIC, by changing the samples' storage conditions.
  
  
  METHODS
  The water sorption, the flexural strength, the flexural elastic modulus, the Vickers hardness and the dimensional changes of five resin-modified GICs were measured using specimens aged for 24 h to 3 mon. The specimens were stored at 37 degrees C, either in a dry environment (A), immersed in water (B), stored in a humid environment (C), stored in a humid environment for 1 h and then immersed in water (D), or immersed in water and subsequently dried (B + A). An analysis of variance was used to compare the results.
  
  
  RESULTS
  The resin-modified GIC absorb during the first 24 h large amounts of water (114-172 mg/cm3) compared to the conventional GIC (30-63 mg/cm3). Water alters the physical properties of resin-modified GICs: With regard to dry specimens, a decrease in the flexural strength of 20 to 80% was observed for samples immersed in water. Decreases in their flexural elastic modulus (50 to 80%) and in their hardness (approximately 50%) were also observed. Water sorption also provoked an expansion in volume of the immersed specimens, ranging from 3.4 to 11.3% after 24 h.
  
  
  CONCLUSIONS
  The flexural strength and Vickers hardness of the resin-modified GICs are sensitive to the water contained in the tested specimens. A correlation was established between the decrease in their physical properties and the water uptake. However, it should not be concluded that these materials are not adequate for use in applications in direct contact with oral fluids. Probably, resin-modified GIC placed in oral cavities would not be affected to the same extent as in in vitro tests. In an oral environment, the constituents of saliva will certainly decrease the rate of water sorption and will hence delay its effects.
authors.affiliation: Laboratory of Dental Materials, School of Dentistry, Geneva, Switzerland. cattani@cmu.unige.ch
authors.forename: M A
authors.initials: MA
authors.lastname: Cattani-Lorente
authors.forename: V
authors.initials: V
authors.lastname: Dupuis
authors.forename: J
authors.initials: J
authors.lastname: Payan
authors.forename: F
authors.initials: F
authors.lastname: Moya
authors.forename: J M
authors.initials: JM
authors.lastname: Meyer
mesh_terms: D000042:Absorption; D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry*; D004356:Drug Storage; D004548:Elasticity; D005899:Glass Ionomer Cements / Q000737:chemistry*; D006244:Hardness; D007101:Immersion; D008422:Materials Testing; D012117:Resins, Synthetic / Q000737:chemistry; D018709:Statistics, Nonparametric; D013718:Tensile Strength; D014867:Water / Q000737:chemistry; D017155:Wettability
chemical_list: D003188:Composite Resins; C079765:Fuji II LC cement; D005899:Glass Ionomer Cements; C088835:Photac-Bond; C081144:Photac-Fil; D012117:Resins, Synthetic; C084550:Vitremer; C119198:Vivaglass Fil; D014867:Water