Less Filler, More Fight: A Graphene Oxide–Carbon Nanotube Hybrid Outperforms Carbon Nanotube Alone at an Identical Low Loading in Epoxy Dental Composites

BackgroundAmalgam's retreat under mercury regulation leaves a mechanical gap that composite resins and glass ionomers have not fully closed, keeping nanofiller-reinforced epoxy systems in contention.Carbon nanotubes (CNTs) and graphene oxide (GO), tested separately at high loadings, each strengthen epoxy in a dose-dependent manner.It is unknown whether using both CNT and GO, at the same total filler amount, gives better mechanical properties than CNT alone. AimsTo compare the tensile, compressive, and nanoindentation properties between a low-loading CNT-only epoxy composite and an iso-loaded GO+CNT hybrid carrying the same total nanofiller content, and to characterise CNT dispersion and fracture-surface morphology on field emission scanning electron microscopy (FESEM). Settings and designIn vitro, laboratory-based comparative experimental study across two collaborating institutions. Materials and methodsEpoxy nanocomposites were cast in 12 g batches of Araldite GY 250 resin with Aradur 951 hardener, as either 0.5 wt% multi-walled CNT alone (CNT group; 0.06 g CNT) or a combined 0.25 wt% CNT + 0.25 wt% GO hybrid (0.03 g CNT + 0.03 g GO) -both carrying an identical total loading of 0.5 wt%.Tensile and compressive testing used a universal testing machine (n=5 per group); nanoindentation used a Berkovich diamond indenter (n=5 per group; 25 indents total); fracture-surface morphology was examined by FESEM. Statistical analysisWith five independent specimens per group, results are reported as mean ± standard deviation and group differences were tested by independent-samples t-test (α=0.05),supplemented with Cohen's d given the small sample size.Tensile strength, compressive strength, and strain at peak differed significantly between groups; reduced elastic modulus and hardness did not reach significance at this sample size, though both carried moderate-to-large effect sizes (d=0.60 and 0.83) with post-hoc power of only 13% and 21%, respectively. ResultsThe GO+CNT hybrid outscored the CNT-only composite on every parameter measured despite an identical total filler loading: tensile strength (27.48 ± 0.45 vs. 25.20 ± 0.51 MPa, ~9% higher, t=7.50, p=0.0001), compressive strength (172.46 ± 1.87 vs. 167.06± 1.16 MPa, ~3% higher, t=5.49, p=0.0006), reduced elastic modulus (5.89 ± 0.58 vs. 5.54 ± 0.58 GPa, ~6% higher, t=0.96, p=0.37, d=0.60), and hardness (0.26 ± 0.04 vs. 0.23 ± 0.04 GPa, ~14% higher, t=1.32, p=0.22,d=0.83).FESEM of both composites showed carbon nanotube pull-out and crack-bridging at the fracture surface; the GO+CNT hybrid additionally carried a visibly more textured matrix background consistent with co-dispersed graphene oxide nanosheets, dispersion remaining generally uniform with no large-scale agglomeration in either group.