Effect of continuous longitudinal glass fiber reinforcement on the cantilever beam strength of particulate filler composites.

OBJECTIVE: The objective of this in vitro study was to investigate the effect of continuous longitudinal glass fibers on the bending properties of particulate filler composite resins.

MATERIAL AND METHODS: Four particulate filler composite resins (Tetric Ceram, Point 4, Z250, P60) and one continuous longitudinal glass fiber material (everStick) as reinforcement were selected. Three groups of beam specimens (5 x 5 x 25 mm) for each material were fabricated. For group I, specimens were not reinforced with fibers and were tested as the control group. For group II, specimens were reinforced with 2 layers of the fiber (6.5 vol%), and for group III with 3 layers (9.8 vol%). The specimens were stored at 37 degrees C for 30 days. One end of the beam specimen (14 mm) was fixed in a device, while the other (11 mm) was left free. Cantilever beam strength was measured using a universal testing machine, loading at a distance of 10 mm from the upright support through a steel ball of 2 mm diameter. The loads and deflection at initial failure and at final failure for each specimen were recorded. The data were statistically analyzed using one-way ANOVA and the multiple comparison Scheffé test (alpha = 0.05).

RESULTS: The bending moments of particulate filler composite at final failure, when reinforced with 3 layers of the glass fibers (272.4-325.2 Ncm), were significantly higher than for the composites without fibers. However, the materials reinforced with 3 layers of fibers were not significantly different from the materials reinforced with 2 layers of fibers (234.1-282.6 Ncm). The materials reinforced with 3 layers of fibers exhibited severe deflection at final failure, ranging from 2.8 mm to 3.4 mm. The bending moments of the particulate composites increased linearly with the weight fraction of the fillers, but there was no linear correlation between them when reinforced with fibers.

CONCLUSIONS: The cantilever beam strength of the particulate filler composites increased significantly when layers of fibers were added and as the weight fraction of filler increased, but a higher fiber volume fraction did not lead to a significantly higher cantilever beam strength.