# Antibacterial Ceramics for Dental Applications
## 3 Results and Discussion
### Antibacterial Properties of Cu and Cu Ions
This has a positive effect on the treatment of patients over a long period of time, thus improving the safety and effectiveness of bone substitute materials in clinical practice at the expense of antibacterial  
Figure 6: The hybrid inorganic-organic hydroxyapatite-chitosan granules modified with titanium (Ti-HA/CTS) and copper (Cu-HA/CTS) [42]. Reprinted with permission from Elsevier. activity [42]. To prolong the effectiveness of Cu ions, their release rate in body fluids must be reduced. The different antibacterial activity of Ti and Cu ions cannot be explained only by their different dissolution rates. Ti ions did not exhibit any antibacterial activity on _E. coli_ bacteria, which is due to the different compositions of the cell walls of _S. aureus_ and _E. coli_ bacteria. The enhanced development of _E. coli_ bacteria in the presence of Ti ions can be explained by the catalytic activity of these ions in the intracellular biochemical processes of _E. coli_ bacteria. The authors did not investigate the cytotoxicity of these materials, which is an important factor in dentistry. For their study, [PERSON] et al. [35] used a ceramic synthesized from sodium aluminosilicate powder and copper oxide (NAS/Cu); the concentrations of Cu were 0.3% and 0.6%, respectively. _S. mutans_ bacteria prepared using MTT methods were used to evaluate the antimicrobial activity of the NAS/Cu ceramics. As shown in Figure 8, both NAS/Cu ceramics showed significant antimicrobial activity compared to the control and the pure NAS samples [35]. Figure 8: (**A**) Images of antibacterial activity of NAS/Cu ceramics after 24 h. (**B**) Antibacterial ration of _S. mutans_ after 24 h. (**C**) Images of antibacterial activity of NAS/Cu ceramics and count (**D**) after 72 h [35]. Reprinted with permission from Elsevier. Figure 7: Antibacterial activity of the cements: bacterial growth inhibition as (**A**) plate images (AATCC Test Method 100-2004) and (**B**) as graphs [42]. Reprinted with permission from Elsevier. On the NAS/0.3 Cu ceramic surface, only minute colonization with _S. mutans_ could be observed, while _S. mutans_ was completely absent on the NAS/0.6 Cu ceramic surface [35]. The antibacterial properties of the samples did not change after 3 days, which is a very important result for long-term antibacterial effects on _S. mutans_ (Figure 8C,D). [PERSON] et al. found that NAS ceramics influenced the DNA replication of _S. mutans_ to some extent, while NAS/Cu severely restricted DNA replication due to the penetration of Cu ions into the bacteria nucleoid of _S. mutans_ (Figure 9). Sodium aluminosilicate ceramics doped with 0.6% copper oxide nanoparticles exhibited stable antibacterial activity against _S. mutans_ and excellent biocompatibility [35]. Figure 9 shows the antibacterial activity of Cu ions. Positively charged Cu ions react with the negative charges of the bacterial cell membrane, causing damage and cell death. Cu ions can penetrate bacteria through ion channels and impair their permeability. This can lead to a flow-out of protein from the bacteria, resulting in a reduction in total protein and disrupting the biomolecular activity of the bacteria. Cu ions impair the respiratory chain and gene replication, which leads to the death of the bacteria [35]. For dental materials, the most important issue is biocompatibility. [PERSON] et al. also showed that small quantities of copper nanoparticles had no influence on the biocompatibility of sodium aluminosilicate ceramics while providing antibacterial activity. From these results, it can be concluded that these ceramics could be used in dental restoration to prevent secondary caries.