Hygroscopic expansion and solubility of composite restoratives

Objective To quantify the changes of dimension (vol%), weight (microgram/mm(3)) and the solubility (microgram/mm(3)) 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((R))), an ion-leaching composite (Ariston pHc((R))), two high-density packable composites (Solitaire((R)) and SureFil((R))) and two sub-micron hybrid composites (Pertac II((R)) and Spectrum TPH((R))). Twelve disks of each test material were prepared, 10mm diameter by 1mm thickness. All specimens were kept dry for 48h 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((R)), Penn) at 37 degrees 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((R)) to 2.39% (+/-0.6) for Ariston pHc((R)). Dimensional changes (vol%) values for specimens immersed in artificial saliva were significantly different only for the material Solitaire((R)) (p<0.05). Change in weight (microgram/mm(3)) values were significantly different (p<0.05), according to the immersing solution for the materials Solitarie((R)), Ariston pHc((R)) and Surefil((R)) At 64 days, all specimens gained weight with the exception of the material Ariston pHc((R)) that lost 20.57 microgram/mm(3) (+/-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 microgram/mm(3) (+/-2.7) for Ariston pHc((R)). 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.