# Antibacterial Ceramics for Dental Applications
## 3 Results and Discussion
### Influence of Surface Properties on the Antibacterial Activity of Bioceramics  
Ytria-stabilized zirconia (YSZ) ceramics are widely used for the fabrication of dental and orthopedic implants due to their excellent mechanical strength and aesthetic and biological properties, and they are an alternative material for patients with metal allergies [59; 98]. The largest problem with zirconia restorations is their high hardness, which is responsible for irreversible and irreparable erosion of natural teeth during daily chewing. Zirconia ceramics are biocompatible but not bioactive or antibacterial, which can lead to plaque formation and a high risk of peri-implantitis or even loss of supporting bone [56]. [PERSON] et al. [60] investigated the antibacterial activity of ZrO\({}_{2}\) in 58S bioactive glass. The composition of 58S bioactive glass (BG) was 60 mol% SiO\({}_{2}\), 36 mol% CaO, and  
Figure 14: Antibacterial response of composites (STO_0 to STO_30) against **(a)**_E. coli_ (MTCC_#_1673) and **(b)**_S. aureus_ (MTCC_#_435) bacteria cell lines. Data presented as mean + SD with triplicate determination, n = 3. Differences were considered significant for “\(p\)” value \(<\) 0.05 (\(\tau\)) or 0.01 (**), 0.001 (\(\pi\)) and 0.0001 (\(\pi\)) (One-way ANOVA followed by Bonferroni post-hoc test) [6]. Reprinted with permission from Elsevier. 4 mol% P\({}_{2}\)O\({}_{5}\). CaO was replaced by ZrO\({}_{2}\) at a concentration of 5 mol% (BG-5 Zr) and 10 mol% (BG-10 Zr), respectively. Antibacterial activity was tested against _S. aureus_ bacteria for 14 days. In addition to the antibacterial activity, [PERSON] et al. also examined the bioactivity of BG-5 Zr and BG-10 Zr glasses. As shown in Figure 15, BG-5 Zr exhibited higher antibacterial activity than the other glasses. Furthermore, higher cell proliferation and activity of osteoblasts were observed for BG-5 Zr glass [60]. An alkaline pH range creates an unfavorable environment for bacterial growth and metabolism, causing morphological changes in bacteria and their death. The release of ions and changes in their concentration in the bacterial environment affect the bacterial cell membrane and cause a pressure drop that alters cell size, shape, and membrane tension. The positive charge of Zr\({}^{4+}\) interacts with the negatively charged bacterial cell wall, resulting in the rupture of the walls and, subsequently, cell death [99]. The lower antibacterial activity of BG-10 Zr can be explained by the solubility of the BGs in the SBF medium and the crystallization of the BG. The incorporation of Zr into the structure of the BG reduces the solubility of the BG because Zr is less electronegative than Ca, and the Zr-O covalent bonds strengthen the network of the BG, resulting in lower concentrations of Na\({}^{+}\), Ca\({}^{2+}\), and Zr\({}^{4+}\) in the SBF medium [60]. These ions are responsible for the increasing pH value. The increase in Zr\({}^{4+}\) ions changes the structure of the BG from amorphous to crystalline, which also affects the dissolution behavior of the BG and the corresponding ion concentration, as amorphous BGs exhibit a higher dissolution rate than crystalline ones. This dissolution behavior affects not only the pH value but also cell proliferation. Compared to other samples, BG-5 Zr samples showed a higher increase in cell proliferation and osteoblast-like cell line activity due to the formation of HCA on the BG surface. BG-5 Zr glass can be used as a potential candidate for bone tissue engineering and clinical applications based on the results of long-term studies on antibacterial activity, cell proliferation, and in vivo cytotoxicity tests. The proliferation, growth, and adhesion of bacteria to a surface are influenced by numerous factors, such as chemical, physical, and physicochemical changes.