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Long-term surface micro-hardness of resin-modified glass ionomers
W Kanchanavasita1, H M Anstice, G J Pearson
1Biomaterials Department, Eastman Dental Institute, London, UK.
Objectives:
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.