FESEM Characterization of Fillers in Composite Resins Marketed as Universal

Objectives: To characterize the filler particles of composite resins marketed as universal using a Field-Emission Scanning Electron Microscope (FESEM).
Methods: Eight universal composite resins were analyzed in this study (Table). Three specimens of 2g of each composite resin were dissolved using a variation of the method introduced by Willems.¹ The residue was dried and mounted on sandblasted aluminum stubs with carbon tape and left drying in a vacuum desiccator for 1 week. Stubs were sputter-coated with Ir and observed under a Hitachi FESEM. Ten micrographs for each composite resin were exposed at magnification from 5,000X to 50,000X. Image J software (NIH) was used to analyze the filler particles.
Results: The fillers were quite different with regards to their shape. Only OM had a homogeneous particle distribution with diameter of the spherical microfillers varying from 262 to 282 nm, with 1-3 μm wide sparse clusters. ST displayed a wide range of sharp particles varying from 175 nm to 1.47 μm, apparently without spherical particles or particles below the width of 100 nm. FU contains nanoparticle clusters or aggregates varying in width from 102 nm to 3.95 μm. HA displayed two types of particles: (a) nanofiller clusters with width ranging from 450 nm to 7.26 μm; (b) conventional filler particles with width ranging from 410 nm to 1.02 μm. EU showed two types of particles: (a) regular filler particles ranging from 450 nm to 3.37 μm; and (b) sparse particle clusters varying from 590 nm to 1.75 μm wide. DO and PO also contain heterogenous particles including nanoparticles ranging from 24 to 41 nm.
Conclusions: Recent composite resins that are marketed as universal have a variety of particle dimensions and shapes. Some materials are similar to their respective 'non-universal' predecessors.

1. Willems G (1992). Doctoral thesis, KU Leuven, ISBN 90-9005193-7