# Antibacterial Ceramics for Dental Applications
## 3 Results and Discussion
### Antibacterial Properties of Silver and Silver Ions  
Silver is known for its chemical stability, superior electric conductivity, and catalytic and antibacterial effects. Silver nanoparticles and their salts are used in the biomedical field as antimicrobial agents [2,37,39,45,46,48,55,70,71,70,71]. Ag\({}^{+}\) can have both beneficial and harmful effects, as it can eliminate bacteria and induce cytotoxicity. Silver ions have been reported to be toxic to numerous human cells, such as bronchial epithelial cells, umbilical vein endothelial cells, red blood cells, peripheral blood mononuclear cells, keratinocytes, and liver cells. The cytotoxicity of silver compounds depends more on the concentration of released Ag\({}^{+}\) ions in the cell medium than on the grain size of the nanoparticles of silver compounds [14]. [PERSON] et al. [13] used nanostructured \(\beta\)-AgVO\({}_{3}\) to prepare leucine glass-ceramics with antibacterial activity that pure leucite glass-ceramics do not inherently offer, and various attempts are being made to add such functionality. Leucite glass-ceramics are used in dental prostheses as ceramic substructures or as masking metal frameworks. They consist of 1-4 \(\upmu\)m sized crystals evenly distributed in the glass matrix [5,13,66]. Leucite (KAlSi\({}_{2}\)O\({}_{6}\)) has a tetragonal crystal structure at room temperature, turning into a cubic structure at 673 \({}^{\circ}\)C [72]. These glass-ceramics are highly translucent and chemically inert. Their coefficient of thermal expansion (CTE) is approximately 12.0-12.6 \(\times\) 10\({}^{-6}\) K\({}^{-1}\), making them suitable for application in dental crowns and veneer applications [63]. IPS d.SIGN powder with different contents of \(\beta\)-AgVO\({}_{3}\) (1 wt%, 2 wt%, 4 wt%, 6 wt%) was used. The addition of \(\beta\)-AgVO\({}_{3}\) influenced the phase composition of the glass-ceramic. The crystal phase inthe control samples consisted only of pure leucite. The addition of AgVO\({}_{3}\) reduced the leucite phase, and a new phase of silicate microcline [K\({}_{0.95}\)AlSi\({}_{3}\)O\({}_{8}\)] was formed (Figure 2). The higher the AgVO\({}_{3}\) content, the higher the content of the microcline phase, which is the main phase at a concentration of 6 wt% \(\beta\)-AgVO\({}_{3}\). [PERSON] et al. investigated the antibacterial activity of leucite glass-ceramics against two bacteria, _E. coli_ and _S. aureus_, using the agar diffusion method (Figure 3). As shown in Figure 3, the glass-ceramic modified with 2 wt% or more \(\beta\)-AgVO\({}_{3}\) showed antibacterial activity against Gram-negative and Gram-positive bacteria. The release of Ag\({}^{+}\), V\({}^{4+}\), and V\({}^{5+}\) ions is very important for the observed antibacterial activity. The main problem with such types of modified ceramics is their increasing solubility beyond the limits for dental ceramics used in contact with cells and the oral cavity, as specified in ISO 6872:2024 [12]. At a concentration up to 2 wt% \(\beta\)-AgVO\({}_{3}\), the release of metal ions  
Figure 3: IPS d.SIGN samples mixed with different contents of \(\beta\)-AgVO\({}_{3}\) (1 wt%, 2 wt%, 4 wt%, 6 wt%) to evaluate their antibacterial activity, in Mueller–Hinton agar plate tests with (**a**) _E. coli_ and (**b**) _S. aureus_[13]. Reprinted with permission from Elsevier. Figure 2: SEM images of IPS d.SIGN samples mixed with different contents of \(\beta\)-AgVO\({}_{3}\): (**a**) control, (**b**) 1 wt%, (**c**) 2 wt%, (**d**) 4 wt%, (**e**) 6 wt%. Leucite is represented by a red arrow and microline phase by a yellow arrow [13]. Reprinted with permission from Elsevier. exceeded the maximum limit. The release of Ag\({}^{+}\) ions for 1 wt% \(\beta\)-AgVO\({}_{3}\) was less than 10 \(\upmu\)g/L for silver ions and 50 \(\upmu\)g/L for vanadium ions. The concentration of released silver and vanadium ions from samples with 6 wt%/\(\beta\)-AgVO\({}_{3}\) in the medium was drastically higher. The progressive increase in the concentration of dissolved ions can be explained by the solubility of the ceramic [13].