Influence of periodontal ligament simulation on bond strength and fracture resistance of roots restored with fiber posts

Abstract

Objective: Considering that periodontal ligament simulation may influence the stress distribution over teeth restored with intraradicular retainers, this study aimed to assess the combined effect of mechanical cycling and periodontal ligament simulation on both the bond strength between fiber posts and root dentin and the fracture resistance of teeth restored using glass fiber posts.

Material and methods: Ninety roots were randomly distributed into 3 groups (n=10) (C-MC: control; P-MC: polyether; AS-MC: addition silicone) to test bond strength and 6 groups (n=10) (C: control; P: polyether; AS: addition silicone, without mechanical cycling, and C-MC, P-MC and AS-MC with mechanical cycling) to test fracture strength, according to the material used to simulate the periodontal ligament. For the bond strength test, fiber posts were cemented, cores were built, mechanical cycling was applied (2×10(6) cycles, 88 N, 2.2 Hz, and 45º incline), and the teeth cut into 3 slices (2 mm), which were then subjected to the push-out test at 1 mm/min. For the fracture strength test, fiber posts were cemented, cores were built, and half of the groups received mechanical cycling, followed by the compressive strength (45° to the long axis and 1 mm/min) performed on all groups.

Results: Periodontal ligament simulation did not affect the bond strength (p=0.244) between post and dentin. Simulation of periodontal ligament (p=0.153) and application of mechanical cycling (p=0.97) did not affect fracture resistance.

Conclusions: The materials used to simulate the periodontal ligament did not affect fracture or bond strength, therefore periodontal ligament simulation using the tested materials could be considered optional in the conditions of the study.

Figure 2

Scanning electron microscopy images. (A) Cohesive failure in dentine. (B) Mixed adhesive/cohesive failure. (C) Adhesive failure between dentin and cement

Figure 3

Graphics of groups addition silicone (A), polyether (B), and control (C) illustrating the force (N) and deformation (mm) of each specimen during the fracture strength test. In the groups with an artificial periodontal ligament, the specimens are accommodated when a load is applied. This is not observed in group C because of the rigidity of the acrylic resin, and the graphic is a crescent line until the failure threshold of the restorative assembly is reached

Figure 4

(A) Schematic diagram of the specimen positioned for the test, indicating the minimal thickness area (lingual portion) of the core where the fracture initiates. (B) Stereomicroscope representative image of specimen fractured in the mesiodistal direction (group C). (C) Root fracture associated with core fracture (group addition silicone) after the fracture resistance test

Figure 5

Scanning electron microscopy image of control group. There is displacement of the buccal surface of the core, exposing the post. The fiber post suffers a crack in the mesiodistal direction, which is a consequence of shear stress above the post. (A) Minimal thickness area and hackle lines (black arrows) indicating the start of the fracture. (B) Hackle lines (white arrows) initiating at the composite/post interface. (C) Hackle lines (white arrows) indicated in the buccal surface showing the fracture propagation