The Marginal Fit and Fracture Resistance of Four‑Unit Monolithic and Bi -layered Zircon Fixed Dental Prosthesis

Purpose: This study aimed to evaluate the fit and fracture resistance of monolithic and Bi -layered zircon fixed dental prosthesis.
Materials and Methods:20 master models composed of two metal abutments and embedded vertically in autopolymerizing acrylic resin blocks to mimic clinical conditions for a four‑unit FDPs. Twenty FDPs were fabricated and divided into two groups (n = 10): group A, bilayered zirconia four‑unit FDPs; group B, monolithic zirconia four‑unit FDPs. The marginal gap of each retainer specimens was measured for both groups at 18 sites on the margin of the master dies using a digital microscope. Paired t-test was used to evaluate mean marginal gap changes. One-way ANOVA and post hoc tests were also employed for comparison among 2groups (α=.05). the Samples in each group were cemented to their corresponding model and then underwent artificial ageing by thermocycling of 5000/cycle. The fracture resistance test was done using universal testing machine at cross-head speed of 1 mm/min. Statistical analysis of the results and comparison between each two groups were performed using independent t,test (significance: P ≤ 0.05).
Results: Marginal gap was increased after porcelain veneering. The mean marginal gap values after veneering in the layering group (52.06 µm) was higher monolithic group (21.4 µm) in molar die margin CONCLUSION Three veneering methods altered the marginal fit of zirconia copings. All ceramic crowns made through two methods revealed clinically acceptable marginal fit.