Ceramics are versatile materials known for their exceptional properties such as high-temperature resistance, electrical insulation, and wear resistance. In this article, we will explore some of the commonly used ceramics, their applications, and distinctive features. One material that has become increasingly popular in dentistry is zirconia ceramic.
Zirconia ceramic was initially used as a prosthetic framework material for veneering with ceramics. However, it can also be used to create monolithic restorations. It is available as a monochromatic uniform material that can be stained by infiltration if required. There is a rising trend to use polychromatic CAD/CAM blocks and disks that imitate the color variation from dentin to the enamel.
Pure zirconia exists in three forms: monoclinic, tetragonal, and cubic. Monoclinic is stable up to 1,170°C, while tetragonal and cubic occur when the temperature exceeds 2,370°C. The tetragonal to monoclinic transformation involves a shear strain and a large (4%) volume increase. This volume increase can close cracks, leading to large increases in the fracture toughness of the material.
Using this transformation toughening in practice requires stabilizing the tetragonal or cubic phases at room temperature. This is typically done by alloying pure zirconia with oxides such as yttrium, magnesium, calcium, and cerium, which will completely or partially stabilize either of these phases. A classification of zirconia ceramics has been proposed based on their microstructure as fully stabilized zirconia (FSZ), partially stabilized zirconia (PSZ), and tetragonal zirconia polycrystals (TZP).
In FSZ, zirconia is in its cubic form and contains more than 8 mol% yttrium oxide (Y2O3). PSZ is made up of nano-sized tetragonal or monoclinic particles in a cubic matrix, while TZPs are monolithic materials primarily made up of tetragonal phase. TZPs are most commonly stabilized with yttria or ceria. In dentistry, all zirconias are TZP types, most commonly Y-TZP, as this form has the highest strength and fracture toughness after machining and sintering.
There are several stabilized zirconia ceramics available, including Nobel Procera Zirconia, Lava/Lava Plus, In-Ceram YZ, Zirkon, Katana Zirconia ML, Cercon ht, Prettau Zirconia, IPS e.max ZirCAD, and Zenostar.
Zirconia ceramic has emerged as a popular material for use in prosthetic dentistry. Its unique properties make it an excellent choice for creating monolithic restorations. Its classification into different types based on its microstructure can help in selecting the appropriate material. Additionally, the availability of different stabilized zirconia ceramics means that clinicians can choose a product that suits their requirements.
