Monolithic zirconia dental crowns. Internal fit, margin quality, fracture mode and load at fracture

- Monolithic zirconia crowns withstand high loading forces.
- Severity of crown margin defects is correlated with decreasing of load at fracture.
- Production method affects the quality of the crown margin and load at fracture.
- Available dental monolithic zirconia materials have considerable differences.

ObjectiveDental all-ceramic restorations of zirconia, with and without an aesthetic veneering layer, have become a viable alternative to conventional metal-ceramic restorations. The aim of this study was to evaluate whether factors of the production methods or the material compositions affect load at fracture, fracture modes, internal fit or crown margins of monolithic zirconia crowns.MethodsSixty crowns made from six different commercially available dental zirconias were produced to a model tooth with a shallow circumferential chamfer preparation. Internal fit was assessed by the replica method. The crown margin quality was assessed by light microscopy on an ordinal scale. The cemented crowns were loaded centrally in the occlusal fossa with a horizontal steel cylinder with a diameter of 13 mm at 0.5 mm/min until fracture. Fractographic analysis was performed on the fractured crowns.ResultsThere were statistically significant differences among the groups regarding crown margins, internal fit and load at fracture (p < 0.05, Kruskall Wallis). Fracture analyses revealed that all fractures started cervically and propagated to the occlusal surface similar to clinically observed fractures. There was statistically significant correlation between margin quality and load at fracture (Spearman's rank correlation, p < 0,05).SignificanceProduction method and material composition of monolithic zirconia crowns affect internal fit, crown margin quality and the load at fracture. The hard-machined Y-TZP zirconia crowns had the best margin quality and the highest load at fracture. Reduction of margin flaws will improve fracture strength of monolithic zirconia crowns and thereby increase clinical success.