# Antibacterial Ceramics for Dental Applications
## 3 Results and Discussion
### Antibacterial Properties of Strontium  
Strontium cations are known for their role in bone formation and bone resorption due to their osteoinductive and antibacterial properties [86; 87; 88; 89]. These properties are exploited to develop bioceramics for improved bone regeneration and implant integration [90]. Peri-implantiis is a polymicrobial infection that leads to inflammation in the peri-implant mucosa and progressive bone resorption, which may result in implant loss [91; 92]. To prevent the loss of the dental or orthopedic implant, its surface can be coated with antibacterial metal ions [93]. In clinical practice, the successful implantation and long-term use of dental and orthopedic implants depend not only on their antibacterial properties but also on their bioactivity, such as promoting osteocyte adhesion, proliferation, differentiation, stability, biocompatibility, and anticoagulation [93; 94]. [PERSON] et al. [91] investigated the effect of strontium hydroxide on bacteria asso-ciated with peri-implantiis. They used the strains A. actinomycetemcomitans (A.a.), _S. mitis, E. coli, S. epidermidis, P. gingivalis_, and F. _nucleatum_. The antibacterial effect of Sr\({}^{2+}\) ions at concentrations of 10 mM and 100 mM was investigated using the agar plate method. The biofilm viability assay test showed that 100 mM Sr(OH)\({}_{2}\) solution killed all tested bacterial strains. Complete growth inhibition of _S. mitis, S epidermidis_ and F. _nucleatum_ as well as significant growth inhibition of _A.a._, _E. coli_ and _P. gingivalis_ was observed with a 10 mM Sr(OH)\({}_{2}\) solution. Furthermore, 10 mM Sr(OH)\({}_{2}\) demonstrated bactericidal activity against all tested strains, with most bacterial cells partially or completely damaged in a bacterial viability assay [91]. No antibacterial effect was found for a concentration below 10 mM or higher than 100 mM [89]. At a concentration higher than 100 mM, the Sr\({}^{2+}\) ions no longer dissolved properly in the liquid medium and tended to precipitate, which explains the dependence of antibate-rial activity on concentration. The antibacterial activity of Sr ions can be attributed to the higher pH value of the environment, which gradually increases over time due to the release of Sr\({}^{2+}\) ions. Most bacteria prefer to grow at a neutral pH value, and a change in it can affect their growth ability as well as their viability and properties. If the concentration of Sr ions in the local medium is too high, mammalian cells can react similarly to bacteria. This effect must be taken into account when using Sr ions to develop new antibacterial bioceramics. Composite resins are widely used in dentistry due to their aesthetic advantages, high bond strength as a cement, and mechanical reinforcement, but they do not possess any antibacterial properties. If bacteria accumulate at a marginal filling, secondary caries and damage to the composite filling can occur. Thus, researchers focus on developing antibacterial composite resins for long-term use. The challenge is that adding antibacterial agents to the composite resin commonly affects the mechanical properties of the composite resin in such a way that the properties of the composite become insufficient for long-term applications. As an additional negative effect, the antibacterial activity only lasts for a short period. The development of composite resin with long-term antibacterial properties would be highly beneficial clinically. [PERSON] et al. [95] developed a glass (Sr-PBG) made of P\({}_{2}\)O\({}_{5}\) (50 mol%), CaO (15 mol%), Na\({}_{2}\)O (20 mol%), and SrO (15 mol%). They used Filtek Z350 XT as the composite resin. The concentrations of Sr-PBG in the composite resin were 3, 6, and 9%. They used _S. mutans_ to evaluate the antibacterial properties of the new composite resin. As shown in Figure 12, the optical density (OD) of _S. mutans_ decreased with increasing Sr-PBG content in the composite resin [95]. The antibacterial effect of the composite resin containing Sr cations can be explained by two mechanisms.