The Effect of Reinforcement on Fracture Toughness of Provisional Materials

Objective: to measure the fracture toughness of a polymethyl methacrylate resin (PMMA), Coldpac, and a bis-acryl composite (BAC), Protemp 3 Garant, and compare the fracture toughness of the same materials reinforced with stainless steel wire, glass fibers and polyethylene fibers. Methods: four groups of thirteen specimens each from both materials were prepared for the three-point-bending test. Three groups had the different reinforcements. One group without reinforcement served as control. Using a Zwick Universal Testing Machine, specimen deflection and peak load to fracture was recorded from which fracture toughness (K_IC in MNm^-1.5) was calculated. Median values of the groups were compared by means of non-parametric analysis of variance. The results were compared using the Kruskal-Wallis test. A p<0.01 was considered to be significant. Results: for the controls, the fracture toughness for PMMA (K_IC=27.9) was significantly less than for BAC (K_IC=31.2). All three reinforcements increased the fracture toughness of BAC significantly more than for PMMA. The glass fibers and the stainless steel wire significantly increased the fracture toughness for both PMMA (p<0.005 and p<0.0001 respectively) and BAC (p<0.0001), but the polyethylene fibers (p>0.10) did not. For the PMMA, stainless steel wire increased the fracture toughness significantly more than the polyethylene fibers (p<0.0001) but not significantly more than the glass fiber (p>0.10), with K_IC=39.0, 25.8 and 34.4 respectively. Glass fiber increased the fracture toughness significantly more than the polyethylene fibers (p<0.0001). For the BAC, the stainless steel wire increased the fracture toughness significantly more than the polyethylene fibers (p<0.0001) but again not significantly more than the glass fiber (p>0.10), with K_IC=44.0, 33.1 and 42.3 respectively. Glass fibers increased the fracture toughness significantly more than the polyethylene fibers (p<0.005). Conclusion: this study demonstrated that of the three reinforcements tested, polyethylene fibers reinforced the PPMA and BAC materials the least.