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

ObjectiveTo 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.MethodRBCs with microhybrid (Filtek™ Z250), ‘nanohybrid’ (Grandio) and ‘nanofilled’ (Filtek™ 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.ResultsAgglomerated 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 μN) than spheroidal and irregular particles (1389 ± 1342 and 1356 ± 1093 μN, 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.SignificanceThe validity of employing the micromanipulation 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.