Fracture resistances of zirconia, cast Ni-Cr, and fiber-glass composite posts under all-ceramic crowns in endodontically treated premolars

PURPOSE: The aim of the present study was to evaluate the fracture resistances of zirconia, cast nickel-chromium alloy (Ni-Cr), and fiber-composite post systems under all-ceramic crowns in endodontically treated mandibular first premolars. MATERIALS AND METHODS: A total of 36 extracted human mandibular premolars were selected, subjected to standard endodontic treatment, and divided into three groups (n=12) as follows: cast Ni-Cr post-and-core, one-piece custom-milled zirconia post-and-core, and prefabricated fiber-glass post with composite resin core. Each specimen had an all-ceramic crown with zirconia coping and was then loaded to failure using a universal testing machine at a cross-head speed of 0.5 mm/min, at an angle of 45 degrees to the long axis of the roots. Fracture resistance and modes of failure were analyzed. The significance of the results was assessed using analysis of variance (ANOVA) and Tukey honest significance difference (HSD) tests (α=.05). RESULTS: Fiber-glass posts with composite cores showed the highest fracture resistance values (915.70±323 N), and the zirconia post system showed the lowest resistance (435.34±220 N). The corresponding mean value for the Ni-Cr casting post and cores was reported as 780.59±270 N. The differences among the groups were statistically significant (P<.05) for the zirconia group, as tested by ANOVA and Tukey HSD tests. CONCLUSION: The fracture resistance of zirconia post-and-core systems was found to be significantly lower than those of fiberglass and cast Ni-Cr post systems. Moreover, catastrophic and non-restorable fractures were more prevalent in teeth restored by zirconia posts.