**3.3 Alumina implants**

Alumina is very inert and resistant to corrosion in an in vivo environment [105]. It elicits minimal response from the tissues, and remains stable for many years of

*Recent Advances in Ceramic Materials for Dentistry DOI: http://dx.doi.org/10.5772/intechopen.96890*

service. Few minutes after the implantation of alumina device, proteins and other biomolecules adsorb on its surface, to form a fibrous capsule around the implant that protects it from immune system. The fact that alumina is biocompatible does not mean that tiny particles formed by the implant wear cannot generate a significant foreign body reaction [106]. Hence, α-alumina is dense (with a specific gravity of 3.97), nonporous, and nearly inert material. It is extremely hard and scratchresistant (9 on the Mohs scale, next only to diamond). It has excellent corrosion resistance in vivo environments (**Figure 12**). Dense alumina implants were used as dental implants, since the 70's, because of their excellent wettability, allowing them to easily adsorb water and biomolecules, resulting in a low coefficient of friction. However, the most disabling property of alumina is its brittleness (high elastic modulus), hence the need to optimize the composition, the porosity and the grain size to improve the mechanical properties of alumina, such as strength, fatigue resistance and fracture resistance. Because of the better resistance to fracture and the higher bending strength (13.000 kg/cm<sup>2</sup> ) of single crystal alumina, compared to that of polycrystalline alumina (3500 kg/cm2 ), single crystal alumina is used for dental implants. Thus, a typical alumina implant is made of single crystal alumina cylindrical core around which polycrystalline alumina is fused. Currently, alumina dental implants are declining in popularity and being replaced by other material having better properties [107].

### **3.4 Zirconia implants**

The demand for zirconia dental implants are increasing recently. In comparison with the Ti dental implants, their increased esthetic, due to similarity to the human tooth color, is the main benefit of these implants [88, 108].

Zirconia with better optical, esthetic, mechanical and biological qualifications, is a hopeful substitute to traditional Ti implant system for oral recovery [109], and is produced by the oxidation of zirconium [110]. Zirconium, which is a transition metal [111], with gray white color [112], can be used to make zirconia implant. Segments of the metal implant can be uncovered by recession of gingiva and the loss of apical bone, which this can disclose a discolored overlying gingiva [113]. These concerns make an opportunity to use the zirconia ceramics because they enjoy great esthetic, biological and mechanical characteristics and they also lack electrically corrosion. Polyethylene and Ti show more inflammatory reactions than zirconia. Less inflammatory response along with the lack of mutagenicity and toxicity in zirconia, can be considered as the most attractive zirconia properties [114]. Zirconia-based ceramics are attractive materials because they exhibit satisfying strength (more than 1000 MPa) and toughness (about 6–10 MPa m1/2), allowing them to contribute

### **Figure 12.**

*Nanoporous alumina fabricated using the anodization process (left and center). Osteoblast interaction with the nanoporous architecture (right) [106].*
