Methods: A total of 90 single rooted maxillary central incisors were decoronated 15 mm above the root apex. They were endodontically treated and randomly divided into 3 groups of 30 samples. Each group was restored using three different post systems: RelyX™ fiber post (3M/ESPE, USA), Radix™ Fiber post (Dentsply/Maillefer, USA) and ParaPost® XH (Coltène/Whaledent, USA). Each group was further divided into 3 subgroups of 10 specimens; each with a different post length (10.0, 7.5, 5.0 mm respectively). All posts were luted using RelyX Unicem resin cement, (3M/ESPE, USA). The specimens were placed in a custom jig, fixed in an Instron testing machine and loaded with a static force at a crosshead speed of 0.5 mm/min 135° to the long axis of the root until failure occurred. The load at failure and mode of failure were recorded.
Results: One-way ANOVA test showed a significant difference in fracture resistance between the 3 subgroups restored with ParaPost system (p=0.025). No significant difference was found within the fiber post groups (Radix, p=0.550 and RelyX, p=0.271). Post Hoc test revealed that the 7.5mm ParaPost group had significantly higher fracture resistance than the 5mm group (p=0.021). Subgroups with 5mm post length displayed the highest percentage of unfavorable failure patterns (ParaPost = 80%, Radix = 50%, RelyX = 60%).
Conclusions: Shortening post length has no significant effect on the fracture resistance of endodontically treated teeth restored with either fiber posts. The prefabricated titanium posts however, showed significantly reduced fracture resistance when shortened to 1/3 the canal length. Regardless of the post system used, roots restored with the short posts (1/3 the canal length) have a higher percentage of unfavorable root fractures.