Water sorption and expansion in resin-composites.

Objectives: To assess the long-term water sorption, solubility and extent of hygroscopic expansion processes of resin-composites with and without incorporated short fibres.
Methods: Three resin-composites incorporating fibres, additional to particle reinforcement, were examined: everX™ (EVX), NovoPro Fill™ (NPU) and NovoPro Flow™ (NPF). Four composites were used as controls, with only particle reinforcement: Filtek bulk Fill™ (FBF), Filtek bulk one™ (FBO), Filtek XTE™ (XTE), and Filtek Flow XTF™ (XTF). For sorption and solubility measurements, 5 disks measuring 15x2 mm were prepared for each material and photo-cured (5x 20s, 1.2W/cm²). Over a period of 140 d, specimens were weighed at predetermined time intervals, then dried for a further 42 d at 37±1°C, to assess the solubility. A laser micrometer was used to record the mean change in diameter for each specimen, as they underwent the sorption measurement. A one-way ANOVA was carried out at 140 d with Tukey post-hoc tests conducted afterwards (α = 0.05).
Results: Water sorptions were found to range between 20.4 and 30.1 μg/mm. XTF exhibited the highest sorption, followed by EVX and NPF, for which both results were similar. Polymer matrix sorption ranged from 3.4% for NPU to 4.7% for EVX. In terms of solubility, the range was between -1.4 to 4.1μg/mm; XTF was found to have the highest solubility levels, with EVX demonstrating a negative solubility -1.49μg/mm. The hygroscopic expansions at 140 days exhibited results between 1.4 and 2.2%. E-glass fibre reinforced composite (EVX) had the highest expansion (2.2%), while the hydroxyapatite fibre reinforced composite (NPU) had the lowest expansion (1.4%).
Conclusions: The relatively high water sorption and expansion of the short E-glass fibre reinforced composite (EVX) is significant which supports the manufacturers’ recommendations to cap this material with a conventional composite. A nano-fibre containing composite (NPU) had the most favourable outcomes compared to a range of composites, which could be related to matrix compositional differences.