Effect of pre- and postpolymerization on flexural strength and elastic modulus of impregnated, fiber-reinforced denture base acrylic resins.

STATEMENT OF PROBLEM: Impregnated fibers require light polymerization; however, little information exists about how different protocols might affect the mechanical properties of reinforced denture base materials.

PURPOSE: The purpose of this study was to compare the effects of pre- or postpolymerization of preimpregnated fibers on the flexural strength and elastic modulus of a reinforced autopolymerized and a heat-polymerized acrylic resin.

MATERIAL AND METHODS: Seventy-two specimens were divided into 12 treatment groups (n=6), according to type of acrylic resin (autopolymerized or heat polymerized), type of reinforcement, and its pre- or postpolymerization. Impregnated glass fibers (Fibrex-Lab), unimpregnated glass fibers (Fibrante), and ribs made from a restorative composite resin (Z250) were used as reinforcements. The reinforcements were light polymerized either before or after incorporation and processing of the acrylic resins. Specimens were tested in 3-point load and the data were analyzed using 2-way ANOVA and Tukey post hoc test (alpha=.05). Specimens were further examined using light microscopy, atomic force microscopy, and scanning electron microscopy.

RESULTS: Elastic modulus was significantly higher for heat-polymerized acrylic resins than for autopolymerized acrylic resins (P<.001). Prepolymerized fibers increased both flexural strength and elastic modulus of autopolymerized acrylic resins significantly more than postpolymerized fibers (P<.001); however, postpolymerized fibers yielded a higher elastic modulus than prepolymerized fibers for the heat-polymerized material (P<.001).

CONCLUSIONS: Prepolymerized fibers improved the overall mechanical properties of reinforced autopolymerized acrylic resins more than postpolymerized fibers. However, postpolymerization of fibers yielded higher elastic modulus for reinforced heat-polymerized acrylics.