Influence of humidity on dimensional stability of a range of ion-leachable cements

The dimensional changes of a variety of dental restorative materials, occurring during and after setting, were investigated. The materials were tested under four different environmental conditions: 25 degrees C at laboratory humidity, 25 degrees C at 100% humidity, 37 degrees C at laboratory humidity and 37 degrees C at 100% humidity. Two materials setting by an acid-base reaction were also examined when protected with both a conventional varnish and a low-viscosity light-curable resin. The dimensional changes were recorded continuously using linear variable displacement transducers (LVDTs) over periods of up to 2 h. The materials investigated showed varying magnitudes of dimensional change. The shrinkage of conventional glass-ionomer cements (Fuji II and Opusfil) were the highest at 37 degrees C in air. This was attributed to the highest rate of water loss in the most desiccating environment. The shrinkage observed for the materials which set, even only in part, by a polymerization reaction will probably be due to the water loss and/or polymerization shrinkage. Exposure of these materials to a high-humidity environment reduced the shrinkage because of the swelling associated with water absorption. Application of the varnish and the protective resin over the cement surfaces also reduced shrinkage in Fuji II due to prevention of water exchange. The apparatus used in this study provided a simple and reliable method for measuring linear dimensional change. Data obtained in this study were comparable, where appropriate, to the values found in the literature.