Esthetic and Mechanical Comparison of Zirconia 3Y, 4Y and 5Y. (Can they be used equally in all clinical situations?)

Zirconia monolithic dental restorations have gained popularity by being used for fixed dental prosthetic applications (FDP’s). To increase the clinical indications of zirconia, by manufacturing and increasing the yttria content, we can obtain higher translucency in our ceramic restoration. Aim: There have been many studies and research regarding the efficiency of the newer translucent zirconia, 4Y and 5Y, and whether or not they fulfil all the requirements a conventional 3Y-TZP zirconia would. The aim of this review was to clarify the indications of each generation, and what are the aesthetic and mechanical properties and/or advantages and disadvantages of each? Materials/Methods: A series of bibliographic reviews and research articles about the different aspects to be considered were used to fully investigate and understand the mechanical and aesthetic properties of yttrium zirconia restorations, such as Elsevier, Pubmed, and Google Scholar. Key words such as “3Y”, “4Y”, “5Y”, “zirconia restorations”, “dental ceramics”, “translucency” “esthetics”, “mechanical properties”, “esthetic properties”, “yttria stabilized zirconia”, “monolithic zirconia” were used. Results: A total of 16 published articles were found and analysed after following a set of inclusion and exclusion criteria. With these, it was concluded that 3mol% yttria (although providing greater fractures strength) is not a suitable option for anterior restorations, whereas 5mol% yttrium and 4mol% yttrium provided superior translucency. Discussion: The first 3 mol% yttria zirconia generation is renowned for its great mechanical properties, and, consequently, its use to produce all ceramic crowns and FDP’s has increased tremendously in the dental field. Transformation toughening is one of its prime characteristics, meaning they have a higher fracture toughness. There is a lower amount of tetragonal phase in the newer highly translucent 4Y zirconia, meaning a diminished ability of transformation toughening through phase transformation. Despite 5Y’s impeccable translucency and aesthetically pleasing appearance, its downfall is its poor mechanical performance when subjected to certain wear tests and fracture load. Conclusion: If a comparatively stronger material for posterior crown abutments and restorations/crowns is needed, 3Y- TZP zirconia is the preferred choice. Under different circumstances, if the final treatment plan requires a rather aesthetically pleasing anterior restoration, highly translucent 5Y-PSZ or even 4Y-PSZ is the fitter option. Thus, concluding that not all can be used equally in different clinical scenarios.