[Study of the creep of glass-ionomer cements]

The creep and recovery of microspecimens of glass-ionomer cements was studied using a tortional creep apparatus. The purpose was to investigate viscoelastic behavior in a low stress that might result from normal chewing forces. Small stress (2,048 MPa), below the composite resin's proportional limit, was maintained for 3 h and after the stress was released. Recovery was followed for 50 h. The measurements were made on specimens: aged 24 h stored dry at 21 degrees C, aged 24 h stored in distilled water at 21 degrees C, aged 24 h stored in distilled water at 37 degrees C, aged 1 week stored in distilled water at 37 degrees C. The glass-ionomer cements exhibited linear viscoelastic behavior at low deformations. The materials did not recover their original shape after 50 h after the stress was removed. The least amount of creep and permanent deformation exhibited the specimens aged for 1 week in distilled water at 37 degrees C. The influence of dehydration was apparent on specimens measured dry at 21 degrees C. They exhibited the greatest amount of creep and permanent deformation.