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 mannwhitney 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.