Homogenization-analysis of Influences of Filler-shapes on Physical Properties of Composites

Objectives: Usage of composite resins (CR) for posterior restorations have been greatly increasing. For further improvement of the mechanical strength of CR, optimization of contents, sizes, shapes, or geometric layouts of fillers are required. The aim of this study was to assess the influence of filler shapes on physical properties of CR in silico using homogenization-analysis.
Methods: The experimental CR composed of irregular-shaped (IS) silica filler (31.2 vol%) and Bis-GMA/TEGDMA were prepared. The CR specimen was scanned by nano-CT (SkyScan1272) with 500-nm resolution, and ten micro-scale models (100 × 100 × 100 μm) were randomly extracted from a scanned region. The other micro-scale models containing sphere-shaped (SS) fillers with the same volume contents as the experimental CR were designed. Young’s modulus and Poisson’s ratio of each CR in macro-scale were calculated by homogenization-analyses. Homogenization-analyses is a computational methodology for calculating macroscopic responses from a micro-scale structure. Flexural strengths of both CR were predicted by the finite element analysis using Young’s moduli and Poisson’s ratios calculated and compared.
Results: For all of x, y, and z directions, significantly greater Young’s modulus and smaller Poisson’s ratio with the exception of x direction were obtained for CR containing IS fillers than SS fillers (two-way factorial ANOVA, p<0.05). Flexural strength of CR containing IS fillers was significantly greater compared with that of SS fillers-containing CR (Student’s t-test, p<0.05).
Conclusions: The in silico homogenization-analysis demonstrated that CR containing IS fillers had greater flexural strength than CR loaded with SS fillers, suggesting that the mechanical strength of CR can be improved by optimizing shapes of silica fillers.