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 x 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 degrees C and five specimens in artificial saliva (Salivace, Penn) at 37 degrees 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].