The mechanical properties of nanofilled resin-based composites: Characterizing discrete filler particles and agglomerates using a micromanipulation technique

Objective. To assess the mechanical properties of discrete filler particles representative of several inorganic fillers in modern dental resin-based composites (RBCs) and to assess the validity of a novel micromanipulation technique. Method. RBCs with microhybrid (Filtek (TM) Z250), 'nanohybrid' (Grandio) and 'nanofilled' (Filtek (TM) Supreme), filler particle morphologies were investigated. Filler particles were provided by the manufacturer or separated from the unpolymerized resin using a dissolution technique. Filler particles (n = 30) were subjected to compression using a micromanipulation technique between a descending glass probe and a glass slide. The number of distinct fractures particles underwent was determined from force/displacement and stress/deformation curves and the force at fracture and pseudo-modulus of stress was calculated. Results, Agglomerated fillers ('nanoclusters') exhibited up to four distinct fractures, while spheroidal and irregular particles underwent either a single fracture or did not fracture following micromanipulation. Z-tests highlighted failure of nanoclusters to be significant compared with spheroidal and irregular particles (P<0.05). The mean force at first fracture of the nanoclusters was greater (1702 +/- 909 mu N) than spheroidal and irregular particles (1389 +/- 1342 and 1356 +/- 1093 mu N, respectively). Likewise, the initial pseudo-modulus of stress of nanoclusters (797 +/- 555 MPa) was also greater than spheroidal (587 +/- 439 MPa) or irregular (552 +/- 275 MPa) fillers. Significance. The validity of employing the micro manipulation technique to determine the mechanical properties of filler particulates was established. The 'nanoclusters' exhibited a greater tendency to multiple fractures compared with conventional fillers and possessed a comparatively higher variability of pseudo-modulus and load prior to and at fracture, which may modify the damage tolerance of the overall RBC system. (c) 2008 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.