Hygroscopic expansion and solubility of composite restoratives

Objective: To quantify the changes of dimension (vol%), weight (μg/mm3) and the solubility (μg/mm3) of dental composite restorative materials after a period of 64 days immersed in de-ionized water or artificial saliva. Method: Six resin-based composite restorative materials were investigated. An organically modified ceramic (Definite®), an ion-leaching composite (Ariston pHc®), two high-density packable composites (Solitaire® and SureFil®) and two sub-micron hybrid composites (Pertac II® and Spectrum TPH®). Twelve disks of each test material were prepared, 10 mm diameter by 1 mm thickness. All specimens were kept dry for 48 h during polymerization. Two control specimens of each group were kept in a desiccating chamber; five specimens in de-ionized water and five specimens in artificial saliva (Salivace®, Penn) at 37 °C. The diameter of each disc was measured automatically across 200 points by rotation through beam of a laser micrometer. These measurements, together with weight measurements, were carried out at intervals over a 64 day period. The equilibrium value at time infinity, the rate of change and the equilibrium solubility was calculated for each material. Results: At 64 days, the mean dimensional change (vol%) after water immersion ranged between 0.15% (±0.05) for Pertac II® to 2.39% (±0.6) for Ariston pHc®. Dimensional changes (vol%) values for specimens immersed in artificial saliva were significantly different only for the material Solitaire® (p<0.05). Change in weight (μg/mm3) values were significantly different (p<0.05), according to the immersing solution for the materials Solitarie®, Ariston pHc® and Surefil® At 64 days, all specimens gained weight with the exception of the material Ariston pHc® that lost 20.57 μg/mm3 (±6.46). Only the specimens immersed in de-ionized water showed any significant dissolution of the material, with solubility values ranging up to 32.5 μg/mm3 (±2.7) for Ariston pHc®. Significance: Currently available dental composite materials vary significantly in the post-placement expansion behavior demonstrating a lack of consensus view amongst developers as to the most desirable values that should be attained. The nature of the immersing solution in in vitro studies of this nature has a distinct effect on the results obtained for some materials.