# Antibacterial Ceramics for Dental Applications
## 3 Results and Discussion
### Antibacterial Properties of Cu and Cu Ions  
Copper cations exhibit strong antibacterial activity, which can be explained by the disruption of the cell membrane, the alteration of intracellular biochemical processes, and the damage to bacterial DNA and nucleic acids by chelation. Cu ions can bind to the cell walls of bacteria, and by binding to phospholipids, they impair the integrity and function of cell membranes and related proteins. This can lead to alterations in the physico-chemical properties of the membrane and a reduction in membrane fluidity and flexibility. Oxidation of membrane lipids is the fundamental mechanism by which Cu ions destroy  
Figure 5: Scanning electron microscopy (SEM) images of bacterial activity of (**A**) _E. coli_ and _S. aureus_ in control, leucite glass-ceramics (LGC) + 10 Ag, and LGC + 15 Ag samples. (**B**) Digital images of (a) bacterial colonies formed on agar plates colony formation unit method (CFU). (**C**) Bar graph _E. coli_ and _S. aureus_ for both control leucite glass-ceramics (LGC) and 15 wt.% Ag [74]. Reprinted with permission from Wiley. bacteria [24; 25; 75]. The concentration of Cu ions in materials is challenging because Cu is known to have a dose-dependent effect due to its cytotoxicity. An optimal Cu ion concentration has a dual effect: it destroys bacteria and promotes the proliferation of normal eukaryotic cells. Wound healing can also be influenced by Cu ions, as they regulate extracellular matrix remodeling, keratinocyte growth, and integrin production necessary for epithelialization [23]. Calcium phosphate (CaP) ceramics are known for their biocompatibility and bioactivity, which make them superior to other bone substitutes. They can repair broken bones and are thus suitable for use in orthopedics, maxillofacial surgery, and dentistry. Calcium phosphates are available as ceramic blocks, porous sponges, granules, or calcium phosphate-based bone cement [42; 76; 77]. Calcium phosphates inherently exhibit no antibacterial activity, and infections often occur due to improper implantation procedures or inadequate sterilization, which negatively affect the patient's treatment. To avoid such risks, many attempts are being made to endow calcium phosphates with antibacterial properties [8; 78; 38]. [PERSON] et al. [42] investigated the antibacterial activity of hybrid hydroxyapatite/chitosan (HA/CTS) granules and their modification with titanium (Ti-HA/CTS) or copper (Cu-HA/CTS) against _S. aureus_ and _E. coli_ strains. Chitosan and copper ions are well-known for their antimicrobial properties [8; 79]. The concentration of Ti resp. Cu was 5 wt% (Figure 6). TiCl\({}_{3}\) and Cu(N0\({}_{3}\))\({}_{2}\) were used as sources of titanium and copper ions [42]. To investigate the antibacterial activity of these doped materials, four cements were prepared: tricalcium phosphate (\(\alpha\)-TCP) as a control group, HA/CTS, Ti-HA/CTS, and Cu-HA/CTS. Mueller-Hinton agar plates were used to evaluate the antimicrobial activity. Figure 7 shows the results of the bacteria colonization tests on the prepared cement surfaces based on chitosan [42]. The test results showed that the application of hybrid hydroxyapatite/chitosan granules suppressed bacterial adhesion to the surfaces. Titanium-modified biomaterials reduced the accumulation of _S. aureus_ bacteria, but they did not reduce and rather increased the adhesion of _E. coli_ bacteria. On the other hand, Cu-modified biomaterials showed the highest antibacterial activity and prevented the adhesion of _E. coli_ and _S. aureus_ to the surfaces [42]. The difference between the Ti- and Cu- modified HA/CTS can be explained by their different chemical properties and their ability to form a stable bond to the biomaterials used in dental cements. The release rate of Ti ions from the ceramic composite to the environment is significantly lower than that of Cu ions.