Influence of Different Zirconia Coping Designs on the Fracture Resistance of All-Ceramic Crowns: An In Vitro Study

BACKGROUND AND AIM: Increased demand for metal-free restorations in posterior areas has increased the focus on zirconia restorations because of its advantages in excellent mechanical properties, patient comfort, and acceptance. Although all-ceramic crowns have better biocompatibility and esthetic properties, there are some clinical reasons for the fracture of the veneer or the core materials in the posterior region. This study aims at comparing the influence of zirconia coping designs on the fracture resistance of all-ceramic crowns. MATERIALS AND METHODS: A total of 32 zirconia copings (n = 8 for each group) were designed and fabricated based on the marginal collar height of zirconia coping. The groups were the following: Group 1: 0.0 mm zirconia coping; Group 2: 0.5 mm collar; Group 3: 1.0 mm collar; and Group 4: 1.5 mm collar. All these zirconia copings were veneered with porcelain. Master die with cemented ceramic-layered zirconia copings was tested using Universal testing machine. Data obtained were statistically evaluated by one-way analysis of variance and post hoc test. RESULTS: There was statistically significant difference between the groups with P < 0.001. Group 4 has the highest strength (3318.89 ± 395.67) followed by Group 3 (2910.0 ± 219.22), then Group 1 (2320.02 ± 547.36) that is the control group and the least strength with Group 2 (2286.59 ± 496.66). CONCLUSION: On the basis of the results obtained from this study, it can be concluded that, the more the height of the zirconia collar, the higher the fracture strength of the all-ceramic crowns. Thus ceramic-layered zirconia coping design with 1.5 mm marginal collar height is recommended for functional long life, at least in the posterior higher load-bearing areas with lesser esthetic demands.