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

Objectives. To study hygroscopic dimensional changes in new resin-matrix composites during water sorption/desorption cycles. Methods. Five materials were examined: a self-adhering flowable composite: Vertise (R) 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 (R) Silorane (FS). Five disk-shaped specimens of each material were prepared (15 mm diameter x 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 150 d water immersion and 40 d recondition periods at (37 +/- 1)degrees 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). Results. 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. Significance. 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. (C) 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.