Fatigue Lifetimes of Endodontically Treated Teeth With Coronoradicular Stabilization Posts

OBJECTIVES: To determine the relative effects of coronoradicular stabilization post material and post design on the fatigue resistance of endodontically treated teeth. METHODS: Thirty-six freshly extracted maxillary central incisors were endodontically treated and were assigned to four groups according to the type of post used for coronoradicular stabilization: quartz fiber-reinforced double taper (FDT), quartz fiber-reinforced two-stage (F2S), zirconia double taper (ZDT), and zirconia two-stage (Z2S). Fiber posts were D.T. LIGHT-POST (FDT) and AESTHETI-PLUS POST (F2S) (Bisco). Zirconia posts were copy-milled from Prismatik CZ (Glidewell). All teeth were obturated using the Epiphany (Pentron) system and finished with a composite core (CLEARFIL PHOTO CORE, Kuraray) and ceramic crown (ProCAD, Ivoclar-Vivadent) cemented with Panavia F 2.0 (Kuraray). Teeth were embedded in acrylic holders with simulated PDL (Extrude, Kerr) and subjected to cyclic fatigue (2 Hz, R=0.1) using a servohydraulic machine (MTS Model 858) while submerged in 37oC DI water. Loading was applied 3mm below the incisal edge on the palatal surface at 45-degrees to the long axis. The load amplitude increased during the test according to three load-time profiles: slowly, moderately, or rapidly increasing. The times until fracture were analyzed using step-stress method with an inverse power law life-load relation and Weibull lifetime distribution. ALTAPro7 (Reliasoft) was used to predict the probability of failure versus time. RESULTS: For a constant amplitude (90-N) cyclic load, the predicted Weibull shape parameters were 0.4272 (FDT), 0.2533 (F2S), 0.1395 (ZDT), and 0.1506 (Z2S), and the predicted log median lifetimes were 5.1 (FDT), 13.8 (F2S), 9.3 (ZDT), and 14.1 (Z2S). CONCLUSION: Teeth reinforced with zirconia posts had more variability in fatigue resistance than teeth reinforced with fiber posts. The two-stage post design resulted in greater tooth fatigue resistance than the double taper design. Supported by grants from the Egyptian Embassy (JS2190) and the NIH-NIDCR (DE013358 and DE017991).