Influence of fiber type and wetting agent on the flexural properties of an indirect fiber reinforced composite

Statement of problem. Different fiber types are available for reinforcing composite restorations. Little information exists regarding optimal fiber type/bonding agent combinations. Purpose. This in vitro study examined the influence of storage time and 2 fiber wetting agents on the flexural properties of an indirect dental composite reinforced by 3 fiber types. Material and methods. Three types of fiber (ultra-high molecularweight polyethylene, Kevlar, and Glass fiber) were used to reinforce samples of an indirect composite (Artglass) prepared to test flexural properties. Each fiber type was used to prepare 3 groups of 10 specimens after fiber wetting with an unfilled or a filled resin bonding agent. All fibers were weighed to an accuracy of 0.01 mg to standardize the amount of fiber placed in the base (tensile side) of the specimen preparation mold (2 X 2 X 25 mm). Fiber-reinforced samples wetted with the unfilled resin were stored for 24 hours before flexural testing, whereas separate groups of fiber-reinforced samples wetted with the fined resin were tested after both 24 hours and 6 months storage in water at 37degreesC. Two additional groups of unreinforced composite control specimens (10 samples per group) were prepared, one for each of the 2 storage times, resulting in I I groups total. Mean flexural strengths (MPa) and flexural modulus (GPa) values were determined in a 3-point bend test at a crosshead speed of 1 mm/min by use of a universal testing machine. Comparisons between means were performed with 2- and 1-way analysis of variance tests (alpha=.01) to demonstrate the influence of storage time, fiber wetting agent, and fiber type on the flexural properties of the indirect dental composite tested. Results. Significant increases (124% to 490%) in mean flexural strength (P<.01) were found for all fiberreinforced groups in comparison to the unreinforced controls at both storage time intervals. The silane containing unfilled bonding agent gave the greatest reinforcing effect (364%) when used with the glass fiber material. After 6 months storage in water, a significant decline (28%) occurred in the mean flexural strength of the glass fiber-reinforced specimens (P<.01) when the filled bonding agent was used. Conclusion. Within the limitations of this study, the choice of fiber type and wetting agent was shown to have a significant positive influence on the flexural properties of the fiber-reinforced composite. When used with the silane containing unfilled bonding agent, the glass fiber increased the mean flexural strength of the unreinforced indirect composite by 364%.