Measurement of water sorption in dental composites.

This study measures the changes in dimension and weight resulting from water sorption in light-cured resin-based materials using an innovative computer-controlled laser micrometer and a precision digital balance. Three materials are examined in this study: a micro-filled composite, a dual-cure luting composite and a compomer. Five discs of each test material were prepared, weighed and the size of each disc was measured across sequential diameters by a computer-controlled laser micrometer. Measurements were carried out at intervals over a 24-month period. Significant changes in the rate of percentage weight gain and the rate of percentage linear expansion occurred for up to 90 days for the composite restorative and the luting material and up to 150 days for the compomer. This study concludes that over a period of 24 months, the hygroscopic expansion of the compomer material is significantly greater than that of the conventional composites tested.