The Effect of Finish Line Design on the Fracture Strength of Zirconia Copings

Statement of the problem: One of the major concerns about all ceramic crowns is their fracture resistance.

Purpose: The purpose of this in vitro study was to evaluate the effect of two marginal designs (shoulder 90°, shoulder 135°) on the fracture resistance of zirconia copings.

Materials and method: In this in vitro study, 20 brass dies were prepared using milling machine: 10 with 1mm width shoulder 90° marginal design and the other 10 with 1mm width shoulder 135° finish line design. Zirconia cores with 0.5mm thickness and 30μm cement space were fabricated on brass dies. The copings were cemented on the dies and fracture test was done using a universal testing machine. Data were analyzed using Mann-Whitney test.

Results: The mean value of fracture resistance for shoulder 90° finish line design were 368.3±109.4 N and for shoulder 135° finish line design were 518.4±115.5 N. Data analysis revealed a statistically significant difference between groups (p< 0.05).

Conclusion: The results of this study showed that the finish line design of zirconia copings influences their fracture resistance. A 135° shoulder finish line design can improve the fracture resistance of zirconia crowns.