Analysis of Filler Content and Distribution in Nano-filled Composite Resins

Objectives: Many composite studies use filler loading as the basis for material comparisons and even clinical selection. The objective of this study was to determine the filler weight percent of a distribution of composite resins after ashing in air or using acetone dilution/extraction and to examine the morphology of the particles. Filler content was compared to manufacturer reported data for each technique. Ashing in air is a standardized technique; acetone dilution/extraction is used specifically to remove the organic matrix if prepolymerized particles are included as filler. Methods: Five commercially available composite resins with micro-hybrid (Gradia Direct), microfilled (Durafill) and nanofilled (Majesty, Filtek Supreme, Premise) distributions were evaluated (n=10) for filler content by weight using: (1) ashing in air at 650⁰C and (2) acetone dilution using centrifuge sedimentation and pipette decanting. Size, shape and distribution of the filler particles were examined using scanning electron microscopy (SEM) for both the remaining ash and precipitant. Results: The weight percent of inorganic fillers after ashing ranged from 45.9 to 88.3%. Using acetone as a solvent to remove the uncured organic matrix showed filler by weight between 72.4 and 80.0%. The standard deviations for ashing in air measurements were lower (0.06-0.29) than found with acetone dilution (0.95-3.12). Values for the three nanocomposites were closer to the manufacturer's data than the microfilled and micro-hybrid composites. Photomicrographs of the particles and their distributions will be presented. Majesty had a significantly higher loading than the others by both ashing and acetone; Durafill and Gradia were significantly lower with both techniques (One-way ANOVA, Tukey Test, p<0.05). Conclusions: The filler content by weight of Filtek Supreme was within 6% of the manufacturer's data for both techniques. Majesty and Durafill were within 6% for only the ashing technique.