Reinforced Composite with Pre-Tensioned Fiberglass: The Influence of Prestressing

Objectives: The purpose of this study was to evaluate the influence of prestressing on the flexural properties of two composite resins, a direct composite resin (Quixfil) and an indirect composite resin (Adoro), reinforced with pre-tensioned fiber glass.

Methods: It was accomplished a preliminary compressive strength test of composite resins and the interfacial adherence test among fiber glass and composite resins (pull-out). In the experimental groups, specimens were reinforced with two fiber bundles symmetrically positioned along the bottom and top, pre-tensioned under a load equivalent to 73.5% of tensile strength (0.496 kN). In the control groups, the bundles were positioned exactly as in the experimental groups, except with no previous stress. Additionally, two groups were included in this study with the same dimensions (2x2x25 mm), except with no fiber reinforcement. After 24h storage, specimens were subjected to a three point flexural bending test to establish the flexural module, the deflection regarding the initial failure and the flexural strength. Data were analyzed using ANOVA and Tukey HSD tests.

Results: The results showed that prestressing increased slightly the flexural module of indirect composite resin Adoro (p<0.001), while direct composite resin Quixfil didn't demonstrate significant changes (p>0.05). The prestressed specimens needed to reach greater deflection than specimens with conventional reinforcement (p<0.001) for the beginning of failure process (an increase of 33% for Quixfil and 58% for Adoro). The prestressing also determined significant increments on the flexural strength of specimens (28.3% for Adoro and 33% for Quixfil) (p<0.001).

Conclusion: Prestressing increased the necessary deflection to the occurrence of initial failure, followed by an increase on flexural strength, however without significant variations on the specimens rigidity (flexural modulus).