Objective:
To assess the influence of cyclic loading and a simulated periodontal ligament (PDL) on the in-vitro failure behavior of root-filled premolars with direct resin composite crowns and fiber posts.
Method:
Clinical crowns of 40 single-rooted upper premolars were cut horizontally, 1.5mm above the buccal cemento-enamel junction. Rootcanal treatments were performed and canals were obturated with guttapercha (cold lateral condensation method). The palatal canals were prepared with Parapost drills (diameter 1.25mm, depth 8mm). Press-fit fiber posts (Parapost FiberWhite) were cemented with resin cement (Panavia F). All teeth were reconstructed with a composite crown (Clearfil Photo Posterior) using a mould. Restored teeth were randomly assigned to one of four groups (n=10 each), and were embedded in acrylic. Group 1 and 2 were with a simulated PDL (Express® painted on the roots). Teeth of Group 2 and 4 were submitted to cyclic loading (8 Hz, load 180-300 N, 250.000 cycles). All tooth-crown constructions were subjected to static load at the occlusal surface, with the loading angle 30º to the tooth long-axis. A standard loading device (crosshead speed 0.5 mm/min) was used. Loads until fracture were registered and analyzed using one-way ANOVA. They were assessed being favorable or unfavorable and their frequencies were compared (Fisher's Exact Test).
Results:
Group | PDL | Dynamic preload | Mean Failure Load (SD) [N] | Ratio Favorable/Unfavorable Failures |
1 | Yes | No | 1377 (273) | 3/7 |
2 | Yes# | Yes | 1465 (388) | 4/5 |
3 | No | No | 1238 (171) | 1/9 |
4 | No# | Yes | 1429 (189) | 3/6 |
#one sample was excluded because of test failure.
No significant difference exists among the four groups regarding to mean failure load (P=0.30) or failure mode (P=0.44).
Conclusion:
The use of cyclic loading and a simulated PDL might be unnecessary in this kind of in-vitro load tests since it did not influence the failure behavior.