Method: Three stainless-steel dies were machine milled to simulate an all-ceramic full-coverage preparation of a maxillary first premolar. Three margin designs were prepared: knife-edge (0.1mm), chamfer (0.5mm) and radial shoulder (1mm). The stainless steel dies were duplicated to produce sixty epoxy resin dies. Full-contour monolithic zirconia crowns (InCoris TZI blocks, Sirona, Benshiem, Germany) were constructed using CAD/CAM system (CEREC 3, Sirona, Benshiem, Germany) and divided into three groups (n=20) according to margin design, then sub-divided into two groups (n=10) according to cement type: glass ionomer and self-adhesive resin cement. The inner surfaces of the crowns were sandblasted using 100µm AL2O3at 1 bar (Renfert basic classic sandblaster, Hilzingen, Germany), then cemented on their relevant epoxy resin dies and loaded to fracture in a universal testing machine (LRX-plus, Llyod instruments Ltd., Fareham, UK) at a crosshead speed of 0.5mm/min.
Result: Two-way ANOVA and Post Hoc tests at a significance level of p≤0.05 showed significant difference between the radial shoulder (2732.78±468.32 N) and the knife edge margin designs (2051.97±719.03 N), however, there was no significant difference between the chamfer (2585.61±343.88 N) and both the radial shoulder and the knife edge. Significant difference was found between resin cement (2818.89±365.67 N) and glass ionomer cement (2094.68±563.93 N).
Conclusion: Adhesive cementation substantially increased the fracture resistance of monolithic zirconia crowns. Knife edge margin design is a promising conservative alternative, though it has the lowest fracture resistance, it is still higher than maximum bite forces. Full-contour monolithic zirconia crowns can be used with any margin design when cemented with resin cement.