Fracture Resistance and Failure Mode of Polyethylene Fiber-reinforced Resin-based Restorations in Structurally Compromised Premolars: an in Vitro Study
To evaluate the effect of polyethylene fiber-reinforcement on the fracture resistance and fracture mode of extensive resin-based composite (RBC) restorations in structurally compromised maxillary premolars. Maxillary premolars (54) with specific dimensions and extracted for orthodontic reasons were used. Following mesio-occluso-distal (MOD) cavity preparation and endodontic access, teeth were randomly assigned to one of three restorative protocols (n=18): RBC applied incrementally (I) or reinforced with woven polyethylene fibers (Ribbond) placed horizontally (H) or U-shaped (U). Restored teeth were stored for 45 days in distilled water at 37°C and then loaded monotonically until fracture. Half of the specimens in each group received axial loading (A) and the other half was loaded paraxially (PA). Fracture load data was assessed using two-way analysis of variance and Tukey's post hoc test for multiple comparisons (α=0.05). The fracture initiation and propagation path were analyzed using stereomicroscopy and scanning-electron microscopy. No significant differences were observed for the fracture strength among loading configurations, except for groups IA (825 N) and HA (553 N). Fracture initiated and propagated mainly at and through the RBC restoration in the I group, whereas a shift to the interface was observed in both polyethylene fiber-reinforced groups. Blocking and bridging of cracks were identified around the fibers, especially in specimens of group U. Incorporation of woven polyethylene fibers to reinforce extensive MOD resin-based composite restorations on endodontically treated premolars reduced the occurrence of cohesive fractures in the restorative material but was unable to increase the fracture resistance of the affected teeth.SUMMARY
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Arrangement of woven polyethylene fiber strips in the Ribbond H (A) and U (B) groups. RBC, resin-based composite; RBC-F, flowable resin-based composite.
Loading configuration. (A) Axial loading: the steel piston was applied to the center of the occlusal table, ensuring symmetric contact on both cusps. (B) Paraxial loading: specimens were loaded only on the buccal cusp, simulating excursive movements.
Fracture strength means and standard deviation. Groups with similar lowercase or uppercase letters have no statistically significant differences.
Fracture initiation and propagation modes. The * marks the catastrophic crack origin, black arrows show cohesive fracture propagation within the restoration or within the dentin, and red arrows indicate crack propagation through the interface. Blue arrows point arrested cracks. In (A) and (B) specimens of group I are presented (respectively axial and paraxial loading). Here, cohesive fractures modes within the resin composite predominated. In (C) and (D), characteristic specimens of group RH are presented (respectively axial and paraxial loading). As shown in (C), the polyethylene fiber strip was able to arrest some of the cracks. Characteristic specimens of group RU axially and paraxially loaded are, respectively, depicted in (E) and (F). Here, interfacial fractures were the most common fracture mode, with cracks being arrested by the polyethylene fiber strips (E) or not growing into the restoration (F). Abbreviations: E, enamel; D, dentin; RBC, resin-based composite; R, polyethylene fibers.
Representative micrograph of a specimen of group H. Several cracks initiated from the occlusal surface of the restoration but did not propagate beyond the woven polyethylene fibers. Catastrophic failure was driven by an interfacial crack (*). Insets (A) and (B) show the interaction of a growing crack with the woven polyethylene fibers. Abbreviations: E, enamel; D, dentin; RBC, resin-based composite; RBC-F, flowable resin-based composite; R, polyethylene fibers. Original magnification: overview 88×; inset (A) 1000×; inset (B) 2000×.
Representative micrograph of a specimen of group U. Cracks initiated from the occlusal surface are contained by the woven polyethylene fibers, avoiding their further propagation through the restoration. Catastrophic failure was driven by an interfacial crack (*). Inset (A) shows the interaction of several cracks with the woven polyethylene fibers. In inset (B) a higher magnification of the polyethylene fibers embedded in the flowable resin-based composite is presented. In (C) the propagation of a crack from the RBC and through the RBC-F until reaching the polyethylene fibers is detailed. Abbreviations: E, enamel; D, dentin; RBC, resin-based composite; RBC-F, flowable resin-based composite; R, polyethylene fibers. Original magnification: overview 30×; inset (A) 88×; inset (B) 500×; inset (C) 2000×.
Representative micrograph of the fracture surface of a specimen of group H. Fracture origin is located at the restoration surface (*). In insets (A) and (B) higher magnification micrographs show the interaction between the woven polyethylene fibers and the RBC. Note the presence of voids and defects inside and around the polyethylene fibers. In insets (C) and (D) the interfacial bond is depicted. Note the presence of enamel remnant attached to the RBC, whereas no dentin remained bonded. Abbreviations: E, enamel; D, dentin; RBC, resin-based composite; RBC-F, flowable resin-based composite; R, polyethylene fibers. Original magnification: overview 72×; inset (A) 200×; inset (B) 600×; inset (C) 100×; inset (D) 400×.
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