Effect of Fiber Quantity on Fracture Load of Acrylic FPDs

Objectives: The aim of this study was to evaluate the effect of fiber quantity on the fracture load of long span fiber-reinforced acrylic provisional FPDs. Methods: A total of 105 four-unit PMMA (Tempron) restoring mandibular second premolar and first molar FPDs were fabricated on a stainless steel model. Six groups of acrylic specimens ( n = 15 each) were reinforced with either 4mm fiber in connector between two pontics or 18mm fiber in pontics extend to both sides of abutments respectively, using one or two strands of S2-glass fiber (Fiberkor 2k bundle) or one strand of E-glass fiber (Stick 4k bundle). Unreinforced specimens served as the control. After 600 thermocycles in water baths at 5°C and 55°C, the specimens were temporarily fixed with a provisional cement (Temp Bond) on the stainless steel abutments. All FPDs were subjected to load with a 6mm steel ball on the middle fossa of first molar pontics by a universal testing machine. The values of initial fracture load were recorded and analyzed by ANOVA (1-way, and 3-way with nested effect). Results: The load required to fracture the fiber-reinforced groups, ranged from 634 N (1 strand of 4mm Fibrekor) to 821N (1 strand of 18mm Stick), is significantly higher than that of unreinforced controls (p<0.001). The fracture load of reinforced groups were found statistically significant associated with length of fiber and quantity of fiber (p<.0001, p=0.01, respectively), whereas no significant difference was identified between Fibrekor and Stick reinforcements (p=0.0994). Conclusions: The addition of glass fibers at pontic area improve the fracture load of long span acrylic FPDs , and its reinforcing effect was affected by both fiber length and fiber quantity.