Hygroscopic dimensional changes of self-adhering and new resin-matrix composites during water sorption/desorption...

To study hygroscopic dimensional changes in new resin-matrix composites during water sorption/desorption cycles.

Five materials were examined: a self-adhering flowable composite: Vertise® Flow (VF), a universal composite: GC Kalore (GCK), two micro-fine hybrid composites: GC Gradia Direct Anterior (GDA) and GC Gradia Direct Posterior (GDP), and a posterior restorative composite: Filtek® Silorane (FS). Five disk-shaped specimens of each material were prepared (15 mm diameter × 2 mm thickness) according to ISO 4049. The mean diameter of each specimen was measured by a custom-built laser micrometer (to a resolution of 200 nm) periodically over 150d water immersion and 40d recondition periods at (37 ± 1)°C. Perspex controls were used. Data analysis was performed by repeated measures ANOVA, one-way ANOVA and Tukey's post hoc test (p<0.05).

Differences in hygroscopic expansion were found for all test materials during sorption, ranging from 0.74% (± 0.05) for FS to 4.82% (± 0.13) for VF. The differences were significant for all materials (p<0.001), except between GCK and GDA. The mathematical relationship between diametral expansion and square root of time was non-linear. VF exhibited significant dehydration shrinkage.

The silorane composite FS had the lowest hygroscopic expansion. The extent of compensation of polymerization shrinkage by hygroscopic expansion depends on materials, specimen dimensions and time-scale. So the clinical situation must be taken into consideration in the application of these findings.