# Antibacterial Bio-Based Polymers for Cranio-Maxillofacial Regeneration Applications
## 4 Cements
### Glass Inoner Cements  
In contrast to PMMA-based cements, glass inoner cements (GICs) have an inherent antibacterial activity. Although the action mechanism is not fully understood, some hypotheses have been posed. On the one hand, the low pH of the cement during setting has been proposed as a suitable mechanism to prevent bacterial colonization during the intervention. On the other hand, fluoride and, in some cases, zinc released from GICs might also have an important role in the antibacterial nature of the cement. However, these properties are not enough to avoid the formation of _S. mutans_ biofilms, leading to carious lesions. The addition of antibacterial compounds such as chlorhexidine or eugenol derivatives has also been investigated, but similar results to PMMA-based resins were obtained, with the mechanical properties reduced [115]. In this regard, the addition of bio-based polymers as modifiers to improve both the antibacterial and mechanical properties of commercial GICs is of great interest.  
Different authors have demonstrated the effect of adding low quantities of chitosan to a commercial GIC [116; 117]. On the one hand, there was an improvement in the mechanical properties of the GIC, which they attributed to the interaction via hydrogen bonds between the hydroxyl and acetamide groups of chitosan, and the hydroxyl groups of the inorganic particles with the carboxylic groups of poly(acrylic acid) (PAA), thus resulting in a stiffer network, and diminishing the interfacial tension among all the constituents. On the other hand, fluoride release from the GIC was catalyzed by chitosan due to the entropic gain associated to its release via chitosan adsorption with PAA, forming a polymeric network, which modulates the mechanical properties of the cement and its adhesion capacity to the enamel or the dentin.  
Other authors have studied these effects in depth. For example, [PERSON] et al. added different concentrations of chitosan (from 5 to 50% %/\(\
u\)) to a commercial GIC (GC Gold Label Glass Inoner) and observed that dual effect: the reinforcement of mechanical properties, and the enhancement of its adhesion to the dentine. This effect was obtained only for those composites containing 5 and 10% chitosan, while concentrations over 25% negatively affected the micro-tensile bond strength, and, therefore, the adhesion to the dentin [118]. Similarly, [PERSON] et al. found an increment of 84% in the mean micro-shear bond strength of the 10% v/v chitosan-modified GIC to the enamel compared to the commercial one (Fuji IX) [119]. Regarding antibacterial properties, both articles assessed biofilm formation by _S. mutans_ and found that 10% chitosan-modified GICs thinned the dense bacterial layer observed in control samples. [PERSON] et al. confirmed that higher concentrations of chitosan achieved better antibacterial results, although compromising the mechanical properties [118]. Thus, while above 10% chitosan there was a reduction in fluoride diffusion, the reported bactericidal effects seemed to be mainly caused by the presence of the polymer, and not by the ions. Moreover, a synergistic effect was found in both antibacterial and mechanical properties when combining chitosan and titanium-dioxide nano-powder [120]. [PERSON] et al. also analyzed whether gingival tissue could adhere to a root surface previously restored with a chitosan-modified GIC and, in agreement with the previous works, they reported the characteristic bimodal behavior of the mechanical properties when increasing the content of chitosan, and demonstrated that 2 wt% was the most cytocompatible dose of chitosan for the growth of human gingival fibroblast, due to the faster flow of fluoride ions to the medium, which consequently combined with H+, increasing the medium pH towards neutrality [121].