Flexural Strength of Fiber-reinforced FPD Restorations

Objectives: Fracture of conservative resin fixed partial dentures (FPD) restorations is of concern (Figure 1). Different techniques for reinforcement of such restorations have been suggested. The aim of this study was to determine the flexural strength of three designs of FPD reinforced with commercially available polyethylene fiber.
Methods: A total of 40 specimens were prepared for the flexural strength test. The specimens ( 4X4X30 mm) were divided into 4 groups with and without addition of one full length of plasma-treated woven polyethylene fiber (3-mm Ultra) ,1.5 length and double full lengths. Composite without fibers was used as a control. The specimen dimension is similar to the bulk and length of a conservative Inlay fiber-reinforced FPD (Figure 1). The fiber was impregnated in unfilled wetting resin (Ribbond Inc., Seattle, WA) and placed as close as possible to the tension side of specimen. A thin layer of composite was placed between the two fibers in groups 1.5 and 2. The universal composite used was Estelite Sigma Quick (Tokuyama Dental, Tokyo, Japan). The specimens were tested using Universal Testing Machine (Model 5500—Instron Engineering Corp., Canton, MA) in compression mode with a customized jig at a cross-head speed of 5 mm/min (Figure 2). The mean flexural strength (N) were compared by One-way analysis of variance, followed by the Tukey standardized range test (alpha=.05).
Results:
Mean flexural strength (n = 40) ranged from 135.4 to 250.2 N for three-point bending. All Ribbond reinforcements showed a significant increase (P<.0001) in mean flexural strength over unreinforced controls (Table 1). Double full lengths was significantly stronger than all other groups evaluated (P<.01). However, there was no significant difference between 1 and 1.5 length in the degree of reinforcement.
Control composite group showed clean total fractures (Figure 3A) while all three reinforced types showed incomplete cracks (Figure 3B).
Conclusions:
The addition of fibers to resin FPDs increased flexural strength. Double full lengths was significantly stronger but may be limited by available clinical clearance. In light of this simulated clinical study, it would suggest that fiber-reinforced FPD restorations are viable medium-term management alternatives for patients.