Effect of Ferrule Thickness on Fracture Resistance of Teeth Restored With a Glass Fiber Post or Cast Post.

PURPOSE: To investigate the influence of ferrule thickness on fracture resistance after mechanical cycling of teeth restored with different intracanal posts. METHODS AND MATERIALS: One hundred twenty bovine incisor teeth were randomized into six study groups, based on the intracanal post used (fiber post or cast post and core) and the presence and thickness of a ferrule (without ferrule, presence of 0.5-mm or 1-mm-thick ferrule, retaining unaltered 2-mm ferrule height). The root posts and the metal crowns were cemented using an adhesive cement. The samples were subjected to mechanical cycling (at 37°C, 45°, 130 N, 2.2 Hz, and 2 × 106 pulses). Afterward, they were subjected to a fracture load test at a speed of 0.5 mm/min and on a 45° slope until failure occurred. The failures were classified as favorable or unfavorable. The fracture resistance data were analyzed with two-way analysis of variance and Tukey test. The chi-square test was used to analyze the pattern of failure. RESULTS: When considering the cast post and core, the 1-mm ferrule thickness group presented a higher resistance to fracture than did the group in which a ferrule was not used (p=0.001). When using a glass fiber post, the groups showed no differences in fracture resistance. Overall, 96.7% of the specimens survived the mechanical cycling. Of the fractures, 58.6% of the fractures were unfavorable, while 41.6% were favorable. CONCLUSIONS: A thicker ferrule statistically increased the fracture resistance only for cast post and core when it was at least 1 mm thick, despite causing more unfavorable failures. Thus, ferrule thickness should be considered when choosing different intracanal posts, to reduce the occurrence of unfavorable failures. In the absence of a ferrule, the use of a cast post and core presents more favorable failures, and in the presence of a 1-mm-thick ferrule, the use of a glass fiber post seems to be the best clinical decision.

Fractographical Analysis and Biomechanical Considerations of a Tooth Restored With Intracanal Fiber Post: Report of the Fracture and Importance of the Fiber Arrangements.

OBJECTIVE: This article aims to present a fractographic analysis of an anterior tooth restored with a glass fiber post with parallel fiber arrangement, taking into account force vectors, finite element analysis, and scanning electron microscopy (SEM). METHODS: A patient presented at the Faculty of Dentistry (Federal University of Santa Maria, Brazil) with an endodontically treated tooth (ETT), a lateral incisor that had a restorable fracture. The treatment was performed, and the fractured piece was analyzed using stereomicroscopy, SEM, and finite element analysis. RESULTS: The absence of remaining coronal tooth structure might have been the main factor for the clinical failure. We observed different stresses actuating in an ETT restored with a fiber post as well as their relationship with the ultimate fracture. Tensile, compression, and shear stresses presented at different levels inside the restored tooth. Tensile and compressive stresses acted together and were at a maximum in the outer portions and a minimum in the inner portions. In contrast, shear stresses acted concomitantly with tensile and compressive stresses. Shear was higher in the inner portions (center of the post), and lower in the outer portions. This was confirmed by finite element analysis. The SEM analysis showed tensile and compression areas in the fiber post (exposed fibers=tensile areas=lingual surface; nonexposed fibers=compression areas=buccal surface) and shear areas inside the post (scallops and hackle lines). Stereomicroscopic analysis showed brown stains in the crown/root interface, indicating the presence of microleakage (tensile area=lingual surface). CONCLUSION: We concluded that glass fiber posts with parallel fibers (0°), when restoring anterior teeth, present a greater fracture potential by shear stress because parallel fibers are not mechanically resistant to support oblique occlusal loads. Factors such as the presence of remaining coronal tooth structure and occlusal stability assist in the biomechanical equilibrium of stresses that act upon anterior teeth.

Preliminary results of the survival and fracture load of roots restored with intracanal posts: weakened vs nonweakened roots.

PURPOSE: To evaluate the fracture load and survival rate of weakened and non-weakened roots restored with different intracanal posts. METHODS: Eighty teeth (16 mm) were prepared to a length of 10 mm with a custom drill. Fifty roots were weakened with a tapered diamond drill, and 30 roots were not. The specimens were embedded with acrylic resin up to 3 mm from the coronal aspect, and the periodontal ligament was simulated. The 50 weakened roots were restored with (n=10) CPC-gold (cast post and core made of gold alloy), CPC-Ni (cast post and core made of Ni-Cr alloy), FP (glass fiber posts), FP-W (glass fiber posts with a wider coronal diameter), and FP-CR (fiber posts relined with composite resin). The 30 nonweakened roots were restored with (n=10) CPC-gold, CPC-Ni, and FP. All of the posts were adhesively cemented. All of the specimens were mechanically cycled (37°C, 45°, 130 N, 2.2 Hz, and 1.5 million pulses) and evaluated after every 5 × 10(4) cycles to evaluate the presence of cracks as a primary outcome (event). The specimens that survived cycling were subjected to a fracture load test (load application on the palatal aspect at a 45° inclination). Failure mode was classified as favorable (above the simulated bone level) and catastrophic (below the simulated bone level). Survival rates were estimated using the Kaplan-Meier method. Fracture load data were analyzed using the Kruskal-Wallis test (α=0.05) for weakened roots, one-way analysis of variance, and Tukey test (p<0.05) for non-weakened roots, and Student t-test (p<0.05) compared nonweakened vs weakened roots for the same post system. RESULTS: For the preliminary survival results, FP-W showed a higher survival rate when compared with CPC (gold/Ni). For the fracture load (N), the statistical analysis (p<0.0001) presented differences among the weakened groups: CPC-gold (541.4) = CPC-Ni (642.6) > FP (282.2) = FP-W (274.1) = FP-RC (216.6). No differences were observed for the groups that were nonweakened (majority of favorable failures): CPC-gold (459.3) = CPC-Ni (422.0) = FP (347.9). Weakened roots restored with CPC-gold promoted high values of load fracture and unfavorable failure rates. CONCLUSION: Cast post and cores or fiber posts can be used for restoring nonweakened roots. However, for weakened roots, a fiber post with a wider cervical emerging diameter appears to be a better alternative when compared with cast post and cores.