The in vitro fracture behavior of severely damaged premolars, restored with metal crowns with limited ferrule and several post-and-core systems, was investigated. Crowns of maxillary premolars were removed and canals were prepared with Gates Glidden drills and with Parapost drills. Groups of 11 samples were each treated with cast post-and-cores (Parapost XP, Wironium Plus) (group 1), prefabricated metal posts (Parapost XH) (group 2), prefabricated glass fiber posts (Parapost FiberWhite) (group 3), and custom-made glass fiber posts (EverStick Post) (group 4). Posts and composite cores and metal crowns in groups 2, 3, and 4 were adhesively cemented. Post-and-cores and crowns in group 1 were cemented with phosphate cement. Thermocycling was performed (6,000x, 5-55 degrees C). Two static load tests (30 degrees ) were applied. During the first load test (preloading) no failures occurred. Failure modes from the second load test were categorized into favorable and unfavorable failures. Mean failure loads among the four groups (group 1, 1,845 N; group 2, 1,718 N; group 3, 1,812 N; and group 4, 1,514 N) were not significantly different. Unfavorable failures were root fractures and favorable failures were postcrown displacements. No differences in frequencies of unfavorable/favorable failures were seen among the groups. The results suggest that different post-and-core systems have no influence on the fracture behavior of severely damaged premolars restored with metal crowns with limited ferrule.
"The fracture susceptibility of teeth restored with posts may be related to factors such as the amount of remaining tooth structure, which provides resistance to the fracture of the tooth (Ng et al., 2006), as well as the characteristics of the post, such as the material composition, modulus of elasticity, diameter, and length (Fokkinga et al., 2006). A Root fracture is the most serious type of failure in post-restored teeth (Testori et al., 1993; Wu et al., 2004). "
[Show abstract][Hide abstract] ABSTRACT: The restoration of endodontically treated teeth requires the fabrication of a post and core to provide retention and support for the final crowns. The objective of this study was to compare the fracture resistance of endodontically treated teeth restored with glass fiber post and composite resin cores, customized zirconia posts, and cast metal post and cores. A total of 40 human extracted mandibular first premolars were used for the study. The teeth were randomly divided into 4 groups. Group A represented a control group that did not receive any posts and was filled with core material only; Group B comprised cast metal posts and cores; Group C comprised custom milled zirconia posts and cores; and Group D comprised glass fiber posts. All groups were prepared to receive all ceramic crowns. All samples were subjected to compressive testing with an Instron machine (Universal Testing Machine) and fracture loads and failure patterns were analyzed. The findings indicated a statistically significant difference between the failure loads in the groups studied. The mean load required to fracture the zirconia custom posts was higher (765.1±48.5 N) than the fiber posts and the cast posts and cores (P
"resulting in fewer root fractures     . Other studies claim that if a severely damaged tooth is restored with a metal crown with a ferrule (collar) around the root, the post material does not play a big role in terms of fracture resistance  . On the other hand, there are also studies showing that higher fracture resistance and fewer catastrophic failures are observed in teeth restored without a post       . "
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to evaluate the load-bearing capacity and microstrain of incisors restored with posts of various kinds. Both prefabricated titanium posts and different fiber-reinforced composite posts were tested.
The crowns of human incisors were cut and post preparation was carried out. The roots were divided into groups: (1) prefabricated serrated titanium posts, (2) prefabricated carbon fiber-reinforced composite posts, (3) individually formed glass fiber-reinforced composite posts with the canal full of fibers, and (4) individually formed "split" glass fiber-reinforced composite posts. The posts were cemented and composite crowns were made. Intact human incisors were used as reference. All roots were embedded in acrylic resin cylinders and stored at room temperature in water. Static load was applied under a loading angle of 45° using a universal testing machine. On half of the specimens microstrain was measured with strain gages and an acoustic emission analysis was carried out. Failure mode assessment was also made.
The group with titanium posts showed highest number of unfavorable failures compared to the groups with fiber-reinforced composite posts.
With fiber-reinforced composite posts the failures may more often be favorable compared to titanium posts, which clinically means repairable failures.
Dental materials: official publication of the Academy of Dental Materials 03/2011; 27(6):e107-15. DOI:10.1016/j.dental.2011.02.009 · 3.77 Impact Factor
"complex resistance (Sorensen & Martinoff 1984, Trope et al. 1985, Assif & Gorfil 1994), providing enough retention and stability only for the prosthesis or coronal restorative material (Christensen 1996). In addition, the geometry, extension and mechanical properties of the post (Caputo & Hokama 1984, Sirimai et al. 1999, Fokkinga et al. 2006) could have an effect on dentine stress distribution, reducing the risk of root fracture. Posts with mechanical properties similar to dentine, which may distribute homogenously the stresses induced by occlusal forces, are favourable in reducing the likelihood of tooth fracture (Caputo & Hokama 1987, Boschian Pest et al. 2002). "
[Show abstract][Hide abstract] ABSTRACT: To test the hypothesis that the presence of an anti-rotation device (ARD) and its location can influence the biomechanical behaviour of root filled teeth restored with cast post-and-cores and metallic crowns.
Fifth two bovine incisor roots were selected and divided into four groups (n = 13): Nd- without ARD; Bd- buccal ARD; Ld- lingual ARD; BLd- buccal and lingual ARD. The specimens were restored with cast post-and-cores and metallic crowns. After a fatigue process (3 x 10(5) 50 N), three strain gauges were attached on the buccal, lingual and proximal surfaces and the samples of each group (n = 3) were submitted to a 0-100 N load. Fracture resistance was assessed in a mechanical testing machine (n = 10). Strain values and fracture resistance data were analysed by one-way anova and Tukey Honestly Significant Difference (HSD) test (alpha = 0.05). The failure mode was then evaluated under an optical stereomicroscope. Bidimensional models of each group were generated for finite element analysis (FEA) and analysed using the von Mises criteria.
No significant difference in fracture resistance values and fracture modes occurred between the four groups. The BLd group had higher stress concentrations in the buccal dentine and higher strain values on the proximal surfaces.
The anti-rotation devices did not influence significantly the fracture resistance and fracture mode. However, the stress-strain values were increased when the anti-rotation device was prepared on the buccal and lingual faces concomitantly.
International Endodontic Journal 08/2010; 43(8):681-91. DOI:10.1111/j.1365-2591.2010.01739.x · 2.97 Impact Factor
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