# Antibacterial Ceramics for Dental Applications
## 3 Results and Discussion
### Antibacterial Properties of Strontium
Firstly, the release of ions into the environment increases the osmotic pressure and the pH value, which affect the growth of the bacteria. Secondly, the dissolved Sr ions can cause enzyme modification of the bacteria, leading subsequently to the death of the bacteria [61; 95; 96]. From the results of this study, it can be concluded that Sr-PBG incorporated into the composite resin inhibits the growth of _S. mutans_. In addition, Sr-PBG can be used as a filler for antibacterial dental materials without deteriorating the mechanical properties of the resin. However, the clinical oral environments are very complex, which may affect the properties of the new cement resin. From this point of view, further tests need to be carried out in such environments to clarify the suitability of such antibacterial composite resin. Antibacterial activity has only been tested on _S. mutans_ bacteria. The antibacterial activity of such composite resin needs to be investigated in long-term studies on different bacteria. [PERSON] et al. [61] investigated the antibacterial efficacy of SrO- and ZnO-bioactive glass (BG) scaffolds against _E. coli_ bacteria strains. The composition of the BG was 6 mol% Na\({}_{2}\)O, 8 mol% K\({}_{2}\)O, 8 mol% MgO, 22 mol% CaO, 18 mol% SiO\({}_{2}\), 36 mol% B\({}_{2}\)O\({}_{3}\), and 2 mol% P\({}_{2}\)O\({}_{5}\). CaO was replaced by SrO and ZnO to prepare the doped BG. The concentrations of SrO and ZnO were 5% and 10%, respectively. Furthermore, [PERSON] et al. also investigated the effect of BG, Zn-BG, and Sr-BG on cell proliferation. The results showed that 5 Sr-BG had a stronger effect on cell proliferation than BG alone. The other samples had no significant effect on cell proliferation. Doping with a small amount of Sr promoted cell proliferation, while doping with Zn inhibited it. The degree of inhibition strongly depended on the amount of zinc oxide as well as the composition of the glass and its rate of degradation [61]. As shown in Figure 13, BG alone already offers an antibacterial effect, but Sr-BG and Zn-BG are more effective against _E. coli_ bacterial strains [61]. Trace metals such as iron, zinc, copper, manganese, molybdenum, tungsten, nickel, cobalt, chromium, vanadium, and several other elements play important roles in a variety of biological and chemical processes when present in the optimum concentrations. Some of these metals are of great importance for enzymatic processes, while others can act as electron donors and facilitate the binding of molecules to corresponding receptors [89; 97]. When the concentration of these trace metals increases above the optimal concentration, the bacteria attempt to adapt, and toxic events can occur. Metal ions can impede bacterial proliferation through different mechanisms: (a) enzyme modification, (b) damage to the bacterial cell walls, (c) oxidative stress and intercellular reactive species, and (d) DNA damage and the regulatory roles of DNA and RNA. The antibacterial activity of Sr ions and Zn ions can be explained by two different mechanisms. Sr ions have an effect on bacterial enzymes, which lose their functions  
Figure 12: (**A**) Antibacterial activity of composite resin without Sr-PBG and with Sr-PBG; (**B**) live/dead staining images of bacteria on the surface [95]. and thus lead to the death of the bacteria. Zn cations can also react with electronegative molecules in cell membranes, resulting in the destruction of the cell membrane and subsequently the damage of cell function [69]. Information on the cytotoxicity of the samples and comparisons between Sr ions and Zn ions are missing. The antibacterial effect needs to be investigated in long-term studies. [PERSON] et al. [6] investigated the antibacterial and bioactive properties of 855 bioslass (58 SiO\({}_{2}\)-37 CaO-5P\({}_{2}\)O\({}_{5}\)) and SrTiO\({}_{3}\) (STO). This bioglass is biocompatible and exhibits good mechanical properties due to its high silica concentration.