Marginal Adaptation and Fracture Resistance of Nanozirconia and Zirconium Dioxide All Ceramic Restoration: An In Vitro Study

Abstract

Background: The importance of marginal adaptation for long-term success in all-ceramic crowns is highlighted, especially considering the mechanical strength of zirconia, although concerns about its hydrothermal aging and low-temperature degradation (LTD) persist. To overcome these challenges, researchers have developed NANOZR, a nanocomposite that outperforms traditional yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) in terms of strength and resistance to aging degradation in dental applications.

Aim: To evaluate the marginal adaptation and fracture resistance of NANOZR and Y-TZP CAD/CAM restorations before and after thermomechanical aging.

Methodology: The study involved fabricating crowns using two types of zirconia framework materials (NANOZR and Katana Y-TZP) on epoxy resin dies, with and without thermomechanical aging. Standard tooth preparation procedures were followed, including silicone index fabrication, chamfer preparation, and ensuring total occlusal convergence (TOC). The process included reference die fabrication, scanning, framework designing, milling, sintering, veneering, cementation, and aging using a chewing simulator and thermocycling protocol. Marginal adaptation and fracture resistance were evaluated using digital image analysis and a materials testing machine, respectively.

Results: Y-TZP and NANOZR showed marginal gap differences before and after thermomechanical aging, with Y-TZP exhibiting a higher gap postaging. NANOZR demonstrated significantly higher fracture resistance compared to Y-TZP. A negative correlation was observed between fracture resistance and marginal gap, indicating that higher marginal gaps were associated with lower fracture resistance.

Conclusion: NANOZR restorations have superior marginal adaptability compared to Y-TZP restorations following thermocycling.