Hygoscopic Expansion Behaviour of New Composite Restoratives

Objectives: This study is designed to measure the dimensional changes due to hygroscopic expansion that occur in four commercially available composite restorative materials representing three new formulations and an established reference composite. Method: The materials tested were a conventional composite (Spectrum, Dentsply); a deep-curing single increment placement composite (QuixFil, Dentsply) a recent compomer (Dyract Xtra, Dentsply) and a new nano-filled organic-ceramic hybrid composite (CeramX, Dentsply). 7 disks of each test material were prepared, 10mm diameter by 1mm thickness. All specimens were kept dry for 48hrs during polymerisation. Two control specimens of each group were kept in a desiccating chamber and five specimens in deionized water at 37.0C. The measurements were made automatically by a computer-controlled laser micrometer that incorporates a stepper-motor controlled specimen stage. The diameter of each disc was measured automatically across 200 points by rotation through the laser beam. These measurements were carried out at intervals over a one month period. Results: At one month, different expansion behaviour was noted in each of the materials tested (p<0.01). The mean % changes in volume after water immersion were: Spectrum =0.49%; Quixfil=0.64%; Dyract Xtra=0.88%; CeramX =0.75% (p<0.01). The controls all showed minor progressive shrinkage; Spectrum = –0.24%; Quixfil= –0.14%; Dyract Xtra= –0.28%; CeramX = –0.21%. Conclusions: The new composite materials examined showed greater hygroscopic expansion than the reference conventional composite material. Current composites vary significantly in the post-placement expansion behaviour.