# Virtual Zirconia Implants Replace Titanium Implants?
## 2 What Is a Zirconia Implant? Ceramics are a common material used in dentistry owing to their biology compatibility and long-term durability. The ceramic composites currently in use in medical and dental devices originated from structural materials used in the aerospace and military industry [5]. The first ceramic implant attempt was made of aluminum oxide. However, because of its unsatisfactory toughness and low long-term survival rates, it was withdrawn from the market in the early 1990s [11]. Nowadays, among all dental ceramics, zirconium dioxide (ZrO\({}_{2}\)), also known as zirconia, has arisen as a multipurpose material thanks to its biological, mechanical, and optical properties. Zirconia does not exist as a pure oxide. Therefore, it needs to be extracted from minerals such as zirconate (ZrO2-SiO\({}_{2}\), ZrSiO\({}_{4}\)) and baddeleyite (ZrO\({}_{2}\)) [12]. In order to meet structural demands, zirconia is doped with stabilizers to achieve high strength and fracture toughness. Zirconia structures are characterized in three crystal forms: monoclinic, cubic, and tetragonal. At room temperature, zirconia is in its monoclinic structure and changes into the tetragonal structure at 117 \({}^{\circ}\)C and into a cubic phase at 237 \({}^{\circ}\)C. The cubic phase is unstable and can break into pieces. However, to stabilize the zirconia, CaO, MgO, and Y\({}_{2}\)O\({}_{3}\) (Yttrium) are added to its structure [13]. The properties that make tetragonal zirconia polycrystal a suitable biomedical material are low porosity, high bending, high density, compression strength including low thermal conductivity, high flexural strength, favorable fracture resistance, as well as wear and corrosion resistance [14; 15]. Moreover, the opaque white color of zirconia, as well as its biocompatibility, osseointegration, and low affinity to bacterial plaque, make this composite a good candidate for dental implants [14]. The enhanced aesthetics of zirconia is attributed to its ability to mask dark substrates with good opacity in the visible and infrared spectrum and controlled translucency. The masking ability is due to its grain size being greater than the length of light, high refractive index, low absorption coefficient, and high density with low residual porosity, as well as the presence of various additives, stabilizers, and pigments [16]. On the other hand, zirconia also has some disadvantages as aging or degradation at low temperatures. In the occurrence of water or water vapor, there is a slow transformation from the tetragonal phase into the monoclinic phase. It may lead to slow development of roughness, thus producing progressive deterioration of the material. Aging occurs as a result of compressive stresses and microcracking. It may be predisposed by its manufacturing processes, such as the macroscopic form and the surface features of an implant, but this has not yet been fully explained [16; 17]. The mechanical and physical properties of zirconia implants depend upon its composition, nature of crystals, metastable polymorphic structure, the ratio of the monoclinic to tetragonal phase, percentage of stabilizing metal oxide, the aging process, the macro and micro design of the implant, the nature of the finish line on the implant abutment, the characteristics of implant abutment, and the amount of occlusal load [16]. Likewise, the implants made of titanium, the zirconia implants, also undergo a surface modification to improve their biological responses. The most common are sandblasting, acid etching, selective infiltration technique (coating the surface with glass infiltration and then heating it in temperature higher than glass transition temperature followed by the infiltration of molten glass between the material grains), polishing, laser treatment, and ultraviolet light [13]. Figure 1 presents the advantages and disadvantages of zirconia implants. Nowadays, the main clinical indication of a zirconia implant is the anterior esthetic zone cases, especially in those with a scalloped, thin phenotype gingival architecture.