Objective: Previous studies have indicated hygroscopic expansion of luting agents occurs as a result of water sorption.  This expansion may initially compensate for setting contraction; however, further expansion has been linked to fracture of all-ceramic restorations.  The aim of this study was to determine time-dependent percent (%) volume change and %sorption of 6 luting agents.  Methods: Using mass measurements accurate to 0.001 gram, %sorption and %volume change were determined on luting agent specimens (n=6,10x2mm disks) stored at 37^oC in distilled water.  The %volume change was determined using the hydrostatic principle, which assumes material buoyancy changes depend on volume change. Measurements were made at 1 day and 42 days.  The types of luting agents studied were resin cement (RC), resin-ionomer cement (RI), and glass ionomer cement (GIC). Results:

A 2-factor ANOVA (p£0.05)/Tukey's post hoc indicated that material was a significant factor for both %volume change and %sorption, while time was significant for %sorption only.  Post hoc subsets are indicated as a-c for % sorption and 1-4 for %expansion.  There was a positive correlation between %volume change and %sorption [Pearson's coefficient = 0.660 (p£0.01)].  Conclusion: All the luting agents showed an increase in sorption and volume; however, the resin cement showed the least increase.