Effect of Cyclic Loading on The Fracture Resistance of Bilayered 3Y-TZP and Monolithic Gradient 5Y-TZP/3Y-TZP Zirconia Based Fixed Partial Denture. (In-Vitro Study)

Aim of the Study: This study aims to measure the fracture resistance of a four-unit fixed partial denture constructed from gradient monolithic zirconia 3Y-TZP/5Y-TZP compared to bilayered zirconia 3Y-TZP four-unit fixed partial denture.Background: Developments in dental materials have led to the creation of an innovative strength-gradient zirconia, which merges 3-mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) with 5-mol% yttria-stabilized tetragonal zirconia polycrystal (5Y-TZP). Despite these advancements, there is a lack of information on its fracture resistance behavior. Material and Methods: A standardized stainless-steel master die was designed to replicate a mandibular first premolar and second molar, prepared to receive 4-unit monolithic and bilayered zirconia FPDs. Ten zirconia fixed partial dentures were milled and divided into two groups (n=5): one with 3Y-TZP that was layered by 0.4 mm ceramic veneer, the other group is monolithic gradient zirconia 5Y-TZP and 3Y-TZP. The FPDs underwent cyclic loading in a mastication simulator to simulate six months of clinical use then fracture resistance was measured using a universal testing machine at a crosshead speed of 1 mm/min, and fractographic analysis was conducted using a scanning electron microscope. Results: The highest statistically significant fracture load was recorded in monolithic 5Y-TZP and 3Y-TZP gradient zirconia (844 ± 156 N), while the lowest statistically significant fracture load was recorded in bilayered zirconia 3Y-TZP (601 ± 89 N). Conclusion: The fracture strength of 4-unit gradient multilayered zirconia 5Y-TZP/3Y-TZP was significantly higher than bilayered zirconia 3Y-TZP when both were subjected to fracture resistance tests after mastication simulation.