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Types of Zirconia

2021-11-19 Page view : 64 views

Various types of zirconia are widely used for the fabrication of dental implant superstructures and fixtures. Zirconia–alumina composites, such as ATZ and NanoZR, are adequate for implant fixtures because they have excellent mechanical strength in spite of insufficient esthetic properties. On the other hand, yttria-stabilized zirconia has been used for implant superstructures because of sufficient esthetic properties. They are classified to 12 types with yttria content, monochromatic/polychromatic, uniform/hybrid composition, and monolayer/multilayer. Zirconia with higher yttria content has higher translucency and lower mechanical strength. Fracture strength of superstructures strongly depends on the strength on the occlusal contact region. It suggests that adequate zirconia should be selected as the superstructure crown, depending on whether strength or esthetics is prioritized. Low temperature degradation of zirconia decreases with yttria content, but even 3Y zirconia has a sufficient durability in oral condition. Although zirconia is the hardest dental materials, zirconia restorative rarely subjects the antagonist teeth to occlusal wear when it is mirror polished. Furthermore, zirconia has less bacterial adhesion and better soft tissue adhesion when it is mirror polished. This indicates that zirconia has advantageous for implant superstructures. As implant fixtures, zirconia is required for surface modification to obtain osseointegration to bone. Various surface treatments, such as roughening, surface activation, and coating, has been developed and improved. It is concluded that an adequately selected zirconia is a suitable material as implant superstructures and fixtures because of mechanically, esthetically, and biologically excellent properties.

The number of types of dental zirconia has increased over the past two decades and it is sometimes difficult to choose the adequate type for each restoration. With the advancement of digital technology, it has become possible to fabricate dental restoratives with high fitting accuracy using CAD/CAM systems. In addition, metal-free restorations are of interest for aesthetic and biological reasons. For example, ceramic implant fixtures have replaced titanium implants and are increasing. Zirconia, which has excellent mechanical, aesthetic, and biological properties, is available as a ceramic implant fixture. Although titanium is generally accepted as a reliable dental implant, zirconia is an alternative material to titanium for metal allergic patients and special patients who pursue aesthetics treatment. It is reported that zirconia implants with modified surfaces result in an osseointegration which is comparable with that of titanium implants. In a comprehensive way, osseointegration is defined as ‘a direct structural and functional connection between ordered, living bone and the surface of a load-bearing implant’. Therefore, zirconia is required for surface modifications to obtain osseointegration to bone. On the other hand, materials for implant superstructures can be broadly classified into resin-based, ceramic, and metal materials, and the number of options is increasing. The choice is based on the characteristics of each material whether it is suitable for crowns, abutments, frames, and/or all of them. Dental zirconia has superior properties required for the fabrication of implant superstructures in comparison to other dental materials. In this article, I will introduce the classification and excellent properties of dental zirconia as implant fixtures and superstructures.