Objective: To assess the impact of incorporating various weight fractions of nanometre-sized particulate fillers on specific properties of microfilled composite resin.
Methods: Microfilled composite resin was prepared by mixing 29 wt.% of resin matrix (Bis- GMA/TEGDMA) with the 71 wt.% of silane treated particulate fillers (Ø 0.4 μm). Then, various fractions of nanometre-sized (180 nm) fillers (0, 5, 10, 15, 20, 25, 30 and 35 wt.%) were added gradually using a high-speed mixing machine. For each composite resin, flexural properties (n = 8) were evaluated using a three-point bending test on a universal testing machine (ISO standard 4049). Fourier transform infrared (FTIR)-spectrometry was used to calculate the degree of monomer conversion (DC%). Surface microhardess (Vickers) was also determined. Surface gloss was measured before and after polishing (4,000-grit paper). A two-body wear test was performed in a ball-on-flat configuration using a chewing simulator with 15,000 cycles. A non-contact 3D optical profilometer was utilised to measure wear depth. An analysis of variance (ANOVA) was applied to interpret the results statistically, then a post hoc Tukey analysis was performed.
Results: ANOVA revealed that the fraction of nanofillers had a significant effect (P < 0.05) on flexural modulus, DC%, microhardness, gloss and wear depth. The group without nanofillers showed the highest DC% (56.6%), gloss after polishing (76.2 GU) and wear resistance (24.2 μm) values, whereas the group with 35 wt.% of nanofillers had the highest flexural modulus (9 GPa) and microhardness (70 VH).
Conclusion: It is beneficial to add nanofillers to microfilled composite resin; however, it is essential to assess the proportion ratio carefully. Optimising all the properties of composite resin at once with just one formulation is challenging.
 
Keywords: microfilled composite resin, nanofiller fractions, properties