The effect of length and concentration of glass fibers on the mechanical properties of an injection- and a compression-molded denture base polymer

Statement of problem. Fiber-reinforcement has been used to overcome the mechanical limitations of denture base polymers. One major difficulty in the use of fiber reinforcement has been the addition of fibers during conventional processing methods. Purpose. This study evaluated the effect of various lengths and concentrations of chopped E-glass fiber-reinforcement on the transverse strength, modulus of elasticity, and impact strength of injection and compression-molded polymethyl methacrylate based denture base polymer. Material and methods. Test specimens (n = 10) of 4-, 6-, and 8-mm fiber length and 1%, 3%, and 5% weight fiber concentrations were prepared with either an injection or a compression-molded processing method. Denture base polymer specimens without any fiber reinforcement were used as control for both processing methods. Transverse strength test specimens (65 x 10 x 2.5 mm) were stored in water bath at 37degreesC for 2 weeks. The transverse strength (MPa) and modulus of elasticity (GPa) was measured with the 3-point bending test. Impact strength (kJ/m(2)) test specimens (60 x 7.5 x 4 mm) were tested with the Charpy-type pendulum impact test setup. The data were analyzed with multifactorial analysis of variance and Tukey post hoc tests (alpha = .05). Results. Injection-molded fiber-reinforced groups showed significantly higher transversal strength, elastic modulus, and impact strength compared with compression-molded groups (P < .001). In the injection-molded groups, fiber concentration increased all mechanical properties tested (P < .05), but fiber length only increased transverse strength and modulus of elasticity (P < .05). In the compression molded groups, fiber concentration affected modulus of elasticity and impact strength significantly (P < .05), but fiber length did not show any significant effect on the mechanical properties tested (P > .05). Conclusion. The transverse strength, elastic modulus and impact strength of injection-molded denture base polymer increased significantly with the use of chopped E-glass fibers, whereas the effect was not significant with the compression-molded polymer.