# Antibacterial Ceramics for Dental Applications
## 3 Results and Discussion
### Influence of Surface Properties on the Antibacterial Activity of Bioceramics
The physicochemical changes of the surface, e.g., the wettability of the surface, can contribute to bacterial adhesion during the first stage, followed by irreversible adhesion (molecularly mediated binding between the cell and the surface) in the second stage [100,101]. The antibacterial and cell adhesion properties of zirconia can be modified by changing its texture [56]. Figure 15: The bactericidal percentages at 10 mg/mL for BG-0 Zr, BG-5 Zr, and BG-10 Zr (\({}^{*}\)\(p\) < 0.05 and \({}^{**}\)\(p\) < 0.01) [60]. Reprinted with permission from Elsevier. Self-cleaning surfaces are well known in nature, e.g., lotus leaves. The self-cleaning ability of the lotus leaf is based on a hierarchical double structure with hydrophobic wax droplets that reduce or prevent the adhesion of various contaminants. Such behavior inspired researchers to develop a self-cleaning surface for bioceramics for medical applications [102]. [PERSON] et al. [58] used a carbon dioxide (CO\({}_{2}\)) laser to create micro-grooves and micro-channel microstructures on zirconia surfaces. The laser texturing performed on the YSZ resulted in a change in the wettability of the surface, changing it from hydrophilic to hydrophobic. It was found that the degree of hydrophobicity was higher in the channel-shaped samples than in the grooved-shaped ones. Both zirconia surface textures showed antibacterial activity, but this was more pronounced for the channel-shaped samples, as shown in Figure 16.  
[PERSON] et al. [56] (Figure 17) confirmed that introducing a nature-inspired lotus effect on the YSZ surface with hydrophobic properties can prevent the growth of bacterial colonies, as well as the proliferation and adhesion of _S. aureus_ bacteria, as schematically illustrated in Figure 17. The air gaps of the microtextured surface prevent direct contact with the bacteria, which leads to a reduction of adhering bacteria (Figure 17b). Besides this effect, the microtextured YSZ surface can also interact with the bacteria in a different manner, as schematically depicted in Figure 18. Here, the part of the bacteria adhering to a textured surface ruptures due to irreversible damage to the cell walls, causing the death of the bacteria. This nicely illustrates that modifications of the surface structure can influence the biological responses of biomaterials used in dental implants, such as protein absorption, cell adhesion, proliferation, and antibacterial activity, without altering the chemical composition of the material. Another advantage of lasers is that they are becoming more affordable while offering high flexibility, reliability, reproducibility, and precise ablation capabilities. Figure 16: (**A**) Photographs displaying the distribution of inseminated _S. aureus_ in each 3 YSZ sample; (**a**) nontextured surface; (**b**) micro-grooved surface: (**c**) micro-channeled surface. (**B**) The results of numbers of bacterial colonies and the antibacterial activity of different-textured 3 YSZ zirconia ceramics [58]. Figure 17: Schematic diagram of bacterial adhesion for (**a**) the hydrophilic surface and (**b**) the hydrophobic surface [56]. Reprinted with permission from Elsevier. Nevertheless, the problem with such microtextured surfaces is their long-term antibacterial activity. The accumulation of dead bacteria on textured surfaces can trigger an inflammatory reaction due to an immune response and potentially even alter the textured surface. Therefore, the long-term antibacterial activity of such microtextured surfaces needs to be tested for a better clinical approach on tooth-like surfaces. There are some controversies in the published literature regarding the antibacterial properties of 3 YSZ ceramics. Some authors [56; 99; 103] have reported that dental zirconia ceramics lack antibacterial properties, and peri-implantitis has been observed in zirconia implants. [PERSON] et al. [104] investigated the antibacterial properties of YSZ (3 YSZ), Y\({}_{2}\)O\({}_{3}\), and Zr\({}_{2}\)O\({}_{3}\) powder. _S.