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The Influence of Ferrule on the Marginal Gap and Fracture Resistance of Zirconia Endocrowns.

PURPOSE
To investigate the precementation mean marginal gap, fracture resistance, and mode of failure of monolithic zirconia endocrowns cemented to endodontically treated molar teeth with butt joint porcelain margins and added ferrule preparation designs.


MATERIALS AND METHODS
A total of 20 mandibular molars were endodontically treated and prepared to receive endocrown restorations. The teeth were randomly divided into two groups: Group B had a butt joint porcelain margin, while Group F received additional axial reduction with a shoulder finish line that added ferrule. Monolithic zirconia endocrowns were milled, and the marginal gaps were measured at four locations prior to cementation with resin cement. All samples were subjected to thermocycling, followed by compressive static loading. The maximum load causing fracture and mode of failure were recorded.


RESULTS
The mean load to failure for Group B (5,616 ± 1,503 N) was not significantly different compared to Group F (5,762 ± 1,618 N) (P = .84). Both groups recorded high rates of irreparable fractures (P = .2699, df = 2). The mean marginal gap in Group B (48.20 ± 12.37 μm) was not statistically significantly different compared to Group F (45.14 ± 8.45 μm) (P = .527).


CONCLUSION
The addition of ferrule to the preparation design had no significant effect on the precementation mean marginal gap, fracture resistance, or mode of failure of monolithic zirconia endocrowns cemented to endodontically treated molar teeth. Monolithic zirconia endocrowns failed predominantly in an irreparable manner, but these failures were at high failure loads. The precementation mean marginal gap for both groups was small in comparison to other materials.