Effect of connector size and configuration on the fracture resistance of a long-span implant-supported monolithic zirconia fixed partial denture (An in vitro Study)

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Abstract
Background: Monolithic zirconia fixed partial dentures (FPDs) have gained popularity due to their high strength, biocompatibility and reduced veneer chipping compared to bilayered restorations. However, the connector region remains a critical point of mechanical failure, especially in long span implant supported FPDs subjected to high masticatory forces. The purpose of this in vitro study was to compare the fracture resistance of implant-supported Y-TZP (yttria-stabilized tetragonal zirconia polycrystal) fixed partial dentures (FPDs) with two connector sizes (9 mm² and 12 mm²) and two connector cross-sectional shapes (oval and circular). Methods: Twenty-eight four-unit posterior implant-supported monolithic zirconia FPDs were fabricated. They were divided into two equal groups (n = 14) based on connector cross-sectional shape (oval vs. circular), each further subdivided by connector size (9 mm² or 12 mm², n = 7 per subgroup). A static fracture test was performed by applying an occlusal load at a crosshead speed of 1 mm/min until failure, and the fracture resistance (load to fracture) was recorded. The data distribution was first checked with the Kolmogorov-Smirnov and Shapiro-Wilk tests, which confirmed that the fracture resistance values followed a normal (parametric) distribution. A two-way analysis of variance (ANOVA) was performed to assess the effects of the connector size (9 mm² vs. 12 mm²), connector cross-section (oval vs. circular), and their interaction on the mean fracture resistance. The significance level was set at α = 0.05. Results: Regardless of cross-sectional shape, the 9 mm² connector groups showed significantly lower mean fracture resistance than the 12 mm² connector groups. Regardless of connector size, the oval cross-section groups showed significantly higher mean fracture resistance than the circular groups. Conclusion: Based on the findings of this in vitro study, it can be concluded that increasing the connector cross-sectional area and using an oval connector shape both enhance the fracture resistance of long-span monolithic zirconia FPDs.
Funding Information
  • Al-Azhar University

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