Mechanical Aspects of Wollastonite Microfibre-reinforced Resin Composites

Objectives: Wollastonite is a naturally-occured calcium inosilicate (CaSiO₃) that has needle-like crystalline structure, and also posses apatite formation ability. Thus, it might be potentially useful to create bioactive dental resin composites by using Wollastonite microfibres as reinforcement. The objective of this study was to evaluate the mechanical properties of Wollastonite microfibre-reinforced resin composites (mFRC), with respect to filler dimension and loading volume.
Methods: Five types of natural Wollatonite microfibres with various dimensions (Φ3×22μm, Φ9×50μm, Φ9×125μm, Φ5×55μm and Φ15×250μm) and different volume percentage (40, 50 and 60) were loaded in experimental bisGMA/TEGDMA/HEMA resin. An LED curing lamp was used to polymerize the experimental mFRC with respective moulds for three-point bending (2×2×20mm, n=8), compressive (Φ3×6mm, n=8) and notchless triangular prism (NTP) fracture toughness (6×6×6×12mm, n=6) tests. Scanned electron microscopy (SEM) was used to observe the fractured surface. Statistical analysis was done on SPSS (ver. 22, IBM, NY) with level of significance α=0.05. Two-way ANOVA with Tukey post-hoc test was used to investigate the effects of microfibre dimensions and volume on the mechanical parameters, and one-way ANOVA was used to compare the strength.
Results: Wollastonite mFRC made by 40 vol% of Φ5×55μm gives the best flexural strength (78.23±10.73 MPa) and fracture toughness (1.14±0.23 MPa●m^1/2). Particularly, filler loading of 40 vol% always give a statistically significant higher flexural strength (p<0.01), compressive strength (p<0.05) and fracture toughness (p<0.01) than 60 vol%. Microfibres of approximately 50μm, i.e. Φ9×50μm and Φ5×55μm, give a significant higher flexural (p<0.05) and compressive (p<0.05) strength than Φ3×22μm and Φ15×250μm. The dimensions of Wollatonite microfibres are inversely related to its compressive strength.
Conclusions: Wollastonite microfibres filler loading is crucial and far more important than the fibre dimensions for mFRC mechanical properties.