title: Long-term surface micro-hardness of resin-modified glass ionomers.
abstract: OBJECTIVE
  The presence of a resin component in resin-modified glass-ionomer cements (RMGICs) results in considerable water sorption which may affect the surface hardness of the materials. This study investigated the effect of long-term storage in aqueous solutions on the surface hardness of RMGICs.
  
  
  METHODS
  The surface micro-hardness of four RMGICs stored in either distilled water or artificial saliva was measured using the Wallace microindentation tester at regular time intervals up to 360 days.
  
  
  RESULTS
  There was a substantial increase in hardness during the first day of storage when RMGICs were kept in distilled water. All RMGICs except one liner/base material reached their maximum hardness within 7 days and maintained their hardness for up to 1 year. RMGICs stored in artificial saliva were relatively softer and showed a decrease in surface hardness with time.
  
  
  CONCLUSIONS
  The post-hardening reaction overcame the plasticising effect of water when RMGICs were stored in distilled water. However, progressive and high water uptake of specimens stored in artificial saliva resulted in a decrease in their surface hardness.
authors.affiliation: Biomaterials Department, Eastman Dental Institute, London, UK.
authors.forename: W
authors.initials: W
authors.lastname: Kanchanavasita
authors.forename: H M
authors.initials: HM
authors.lastname: Anstice
authors.forename: G J
authors.initials: GJ
authors.lastname: Pearson
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry; D005899:Glass Ionomer Cements / Q000737:chemistry*; D006244:Hardness; D006245:Hardness Tests / Q000295:instrumentation; D008422:Materials Testing; D012117:Resins, Synthetic; D012464:Saliva, Artificial / Q000737:chemistry; D018709:Statistics, Nonparametric; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D003188:Composite Resins; C079765:Fuji II LC cement; D005899:Glass Ionomer Cements; D012117:Resins, Synthetic; D012464:Saliva, Artificial; C084550:Vitremer; D014867:Water; C067790:Vitrabond; C084541:Fuji glass-ionomer lining cement