**2. Classification of ceramic materials**

Ceramic materials are utilized for several dental applications and are distinguished by their good mechanical properties, high electrical resistance, high thermal conductivity, and excellent biocompatibility. Thus, the oxides, particularly alumina, zirconia, and silica are the most commonly used ceramic materials in the area of dentistry. These materials are classified based on their chemical compositions or based on processing methods.

### **2.1 Based on chemical compositions**

In the past decades, the ceramic materials have attired much attention due to their excellent properties depend to their chemical composition. However, several researches have been studied to develop nanoceramic materials, will be further expanded in future.

### *2.1.1 Silicon oxide ceramics*

Silicon oxides ceramics have been widely employed in biomedical applications because its mechanical stability, biocompatibility, and high specific surface, which can be modified [11–15]. The silanol group on the support of the silicon atom can be activated to make a chemical bond with organosilane, which can also lead to providing various functional groups that can mediate a vast selection of particular bioconjugation strategies [16]. When stable silanes layers are formed on the silicon surface conventional bioconjugation process are used to physisorb or chemisorb a broad bioactive nanoparticles and molecules on the silicon surface.

Zhang et al. [15] observed a reduction of 90% in albumin adsorption on silicon surfaces by 0.05% Tween 20 over 4 h. The self-assembly of polyethylene glycol (PEG) with monomethoxypoly(ethylene glycol) (MPEG) have been used with great success for functionalization of silicon surfaces and for suppressing the adsorption of platelets, fibroblasts, and Hela cells. The water contact angles of the different silicon surfaces are showed in **Table 1**. The maximum value was found for the case of the methylated silicon surface with 2% of dichlorodimethylsilane (in the range of 99–102 °).

Porous silicon (pSi) is a biocompatible and biodegradable material due to its high surface area, which induces a fast oxidation of silicon in aqueous solution [17–19]. Hence, it is shown that particles synthesized out of pSi are biodegradable in plasma, blood, and tissue and then stable [20].

Additionally, the internalization of pSi particles by endothelial cells and macrophages in vivo and in vitro with no adverse effects associated to particles partitioning and cell proliferation [21]. The controlled release of cytokine is near to that of controls, showing that pSi particles are also non-immunogenic. Hence, no toxicity has been revealed in healthy receiving several injections of these pSi particles [22].

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


**Table 1.**

*The water contact angles of different surfaces [15].*

Indeed, polymers coatings have been employed to coat pSi particles to protect them from cellular degradation although the conjugation of antibodies has promoted the efficient delivery of payloads [23].

### *2.1.2 Aluminum oxide ceramics*

Bioceramics (like alumina, zirconia, etc.) are mainly employed in orthopedic and dental reparation. Alumina (aluminum oxide) is the only solid oxide form of aluminum (Al2O3). Thus, corundum is the crystalline form of alumina.

Alumina was first used since the 1970s and its clinical results revealed a fracture rate greater than 13% [24]. However, the disadvantage of these materials was related to the fact that they could not be processed to full final density. In the late of 1980s, a second generation ceramic materials, with a smaller grain sizes and a higher density, was developed. The fracture rate of these materials was less than 5% [25]. Today, a third generation ceramic materials, characterized by high purity, full density, and finer microstructure was appeared. The properties of biomedical grade alumina are illustrated in **Table 2**.

Additionally, it is shown that the degree of tensile bending strength of ultrafine Al2O3 particles is remarkably over that of all other ceramics [27]. The ceramics for substructures of "jacket crowns" enriched by alumina (up to 60% of weight) of different grain size (10–30 μm) have been used to increase the stability. Hence, intense refraction of light takes place at the alumina (in the feldspar) due to the difference in the refraction index between feldspar and corundum.
