In vitro evaluation of fracture resistance and failure mode of internally restored endodontically treated maxillary incisors with differing heights of residual dentin.

STATEMENT OF PROBLEM: Some of the associated effects of different restorative systems placed in endodontically treated teeth with varying heights of residual dentin have yet to be examined in a comprehensive manner. There is a need for additional information regarding fracture resistance and mode of failure. PURPOSE: The purpose of this in vitro study was to evaluate the effect of 3 different restorative techniques with varying amounts of remaining dentin heights on the fracture resistance and failure mode of endodontically treated teeth. MATERIAL AND METHODS: Three groups of 40 human maxillary incisors were subdivided into 4 subgroups (n=10) with respect to the uniform height of the residual coronal dentin, defined as 0-, 2-, 4-, or 5-mm from the cemento-enamel junction, and then restored internally using a composite resin (Z100 MP) (control group), a cobalt-chromium ceramic alloy custom-made cast post and core (IPS d.SIGN 30; CCPC group), or a carbon fiber post system (Tech Xop 2000; CFP group). All specimens were then restored with nonprecious cast crowns. Static loading tests were performed on each specimen until failure (crack without a complete fracture). The data were analyzed with 2-way ANOVA and Bonferroni-corrected t test for independent samples (alpha=.05). Failure was classified as either favorable (allowing repair) or catastrophic (not allowing repair). RESULTS: The fracture resistance values (N) for the 0-, 2-, 4-, and 5-mm residual dentin heights were: 88, 143, 154, and 202 for the control group, 230, 264, 364, and 383 for the CCPC group, and 153, 235, 346, and 357 for the CFP group, respectively. Generally, all the differences tested were statistically significant. The failure mode was catastrophic for no control specimens, for 36 CCPC specimens, and for 4 CFP specimens. CONCLUSIONS: The highest and lowest fracture resistances were recorded for the CCPC and control groups, respectively, at each residual dentin height. An increased height of residual dentin generally provided greater fracture resistance. The fracture resistance of the CCPC group was, however, similar or only slightly higher than that of the CFP group when 2, 4, or 5 mm of residual dentin height was present. In contrast, the failure mode was favorable for almost all of the CFP and control groups, while it was catastrophic in most of the CCPC group.