The Effect of Different Marginal Designs on the Fracture Resistance of Monolithic Zirconia Crowns

Abstract   Background and Aim: One of the major problems of all ceramic restorations is their probable fracture against the occlusal force. The aim of the present in vitro study is to compare the effect of three marginal designs (shoulder, sloped shoulder, chamfer) on the fracture resistance of monolithic zirconia crowns. Materials and methods: In this in vitro study, three PEEK dies with chamfer finish line design (0.8 mm depth), shoulder finish line design (1 mm depth) and sloped shoulder finish line design (1 mm depth) was prepared using milling machine. Thirty epoxy resin dies (10 samples chamfer, 10 samples sloped shoulder, 10 samples shoulder) were made. Monolithic Zirconia crowns with 35μm cement space fabricated on the 30 epoxy resin dies in a dental laboratory. Then the zirconia crowns were cemented on the epoxy resin dies and underwent a fracture test with a universal testing machine STM-20 (SANTAM, Tehran, Iran) and samples were investigated from the point of view of the origin of the failure. All tests were performed in SPSS ver.22 software. Results: The mean value of fracture resistance for the shoulder margins was 3965.80±417.52 N, for the chamfer margins was 4910.40±1002.83 N and for the sloped shoulder was 4490.90±898.48 N. The One-way ANOVA analysis revealed a statistically significant difference between groups (P=0.049) and Tukey post hoc analysis showed that fracture resistance of Chamfer group was significantly higher than Shoulder group (P<0.05). Conclusion: The result of this study indicates that marginal design of the zirconia crowns effects on their fracture resistance. A chamfer margin could improve the biomechanical performance of single zirconia crown restorations. Key words: Marginal Designs, Fracture Resistance, Monolithic Zirconia