Expansion behaviour of compomer restoratives

This study measured the dimensional changes due to hygroscopic expansion that occur in five commercially available compomer restorative materials using a computer-controlled laser micrometer. The materials tested were; [C]=Compoglass-F (Vivadent); [D]=Dyract AP (Dentsply DeTrey); [E]=Elan (Kerr); [F]=F2000 (3M); [H]=Hytac (Espe). Twelve discs of each test material were prepared, 10 mm diameter×1 mm thickness. All specimens were kept dry for 48 h during polymerisation. Two control specimens of each group were kept in a desiccating chamber; five specimens in deionized water at 37°C and five specimens in artificial saliva (Salivace, Penn) at 37°C. The diameter of each disc was measured automatically across 200 points by rotation through the laser beam. These measurements, together with weight measurements, were carried out at intervals over a 2 month period. At 2 months, the mean % changes in volume after water immersion were: [C]=2.45% (SD=0.10); [D]=1.50% (SD=0.12); [E]=1.53% (SD=0.09); [F]=1.69% (SD=0.12); [H]=1.44% (SD=0.18). Specimens immersed in artificial saliva showed expansion rates identical to those immersed in water with the exception of material [H] at 1.73% (SD=0.02) (p=0.01). All specimens immersed in saliva showed a greater weight gain than those in water. The time taken to reach 90% of the final expansion varied from 7 days [F] to 50 days [H].