Effect of Deep Margin Elevation on the Fracture Resistance of Maxillary Molar Zirconia Crowns

The purpose of this in vitro study was to evaluate the fracture resistance of maxillary molar zirconia crowns cemented with deep margins relocated with resin composite.

A maxillary right first-molar typodont tooth was prepared for a complete-coverage zirconia crown and modified to have: (1-DME) a 3 mm deep and 3 mm wide box on the mesial margin; (2-DME) 3 mm deep and 3 mm wide boxes on both the mesial and distal margins; and (N-DME) no box modification. Before the first modification, 45 zirconia (4 mol% yttria) crowns were fabricated. The die was scanned before each modification to fabricate the corresponding 3D-printed dies (n = 15 per group). The DME boxes were restored with universal resin composite, and the crowns were then cemented to their respective dies using a resin luting cement. Then artificial aging was performed by thermocycling for 10,000 cycles between 5 °C and 55 °C with a dwell time of 30 s. The cemented crowns were then loaded to failure in a universal testing machine. Maximum fracture load was analyzed with one-way ANOVA and the post hoc Tukey HSD test (α = 0.05). In addition, fracture patterns were evaluated descriptively with scanning electron microscopy images.

The fracture resistance of maxillary molar zirconia crowns differed significantly among the groups. Group 2-DME demonstrated the highest mean fracture resistance (5370 N), followed by Group 1-DME (5083 N). The lowest mean value was recorded for the control group, N-DME (2961 N).

Zirconia crowns cemented on teeth with deep margin elevation exhibited higher fracture resistance than crowns cemented without deep margin elevation.