# Antibacterialarial Agents Used in Modifications of Dental Resin Composites: A Systematic Review
## 4 Discussion
### Modification of RBC Compositions  
#### 4.2.1 Organic Compounds and Monomers  
Antimicrobial modification of resin monomers allows for a sustained bactericidal effect due to the integration of the agent into the matrix during polymerization. This action will be independent of the filler release process. The action may not be as strong, but it will be long-lasting. Among the most common matrix modifiers are quaternary ammonium compounds (QACs). They disrupt the electrical balance of bacterial cells. One consequence of electrical imbalance is disruption to the bacterial cell wall, resulting in the outflow of cytoplasmic components and, ultimately, bacterial death [14; 15; 23]. [PERSON] et al. made experimental RBCs with potentially antibacterial agents--hexadecyltrimethylammonium bromide (CTAB) and dimethyldioctadecylammonium bromide (DODAB). They then studied the effects of these agents on the mechanical properties of the experimental material. It consisted of a mixture of bis-GMA/UDMA/HEMA/TEGDMA monomers filled with silanized silica (45 wt%). It was shown that the type and amount of modifier affected the flexural strength, hardness, and shrinkage stress. However, the modification did not affect the diametral tensile strength of the experimental composites [65]. Among the most commonly used antibacterial agents are quaternary ammonium (QA) monomers of methacrylate. These agents tend to degrade in the oral environment due to their structure (they contain ester bonds). The use of monomers free of ester bonds may be a way to overcome this problem [23]. [PERSON] et al. [23] used QA monomers based on methacrylamides. Tertiary quaternary ammonium acrylamides (AMs) and methacrylamides (MAMs) with 9- and 14-carbon alkyl side chains were used in the study. The substances were then incorporated into experimental composites, which were based on bisphenol A-glycidyl methacrylate (bis-GMA) and triethylenglycol di-methacrylate (TEGDMA). The study showed that all versions of the composites containing 14 carbons per chain showed strong antibacterial properties, resulting in a twofold reduction in biofilm titers. Evaluation of cytotoxicity showed no significant differences between the control sample and the MAM and AM modifications, which may suggest good biocompatibility of the material with patient tissues. The degree of conversion showed similar levels for all groups tested. Composites modified with MAM and AM with alkyl side chain lengths of 14 carbons showed lower polymerization rates. Flexural strength and modulus values were similar for all groups under dry conditions. But issues related to wet mechanical properties still need to be addressed. [PERSON] et al. [24] synthesized and structurally characterized nine new antibacterial di-methacrylate monomers derived from bis-quaternary ammonium salts (bis-QAMs). In most cases, a complete bactericidal effect was achieved with bis-QAM concentrations below 1 mg/mL. Notably, two of these structures demonstrated comparable or superior activity against _Streptococcus mutans_ compared to MDBP. Moreover, all modified bis-QAMs successfully inhibited _Streptococcus mutans_ biofilm formation at concentrations equal to their MIC values. The monomers used demonstrated low cytotoxicity on human dental pulp stem cells. Cytotoxicity studies should be expanded and long-term effects on tissues should be investigated to ensure high biocompatibility. Also, this study was only focused on resin formulations; hence, the properties and biocidal activity of composites prepared with bis-QAMs must be evaluated. [PERSON] et al. [25] prepared a dental composite with methacrylate-based monomers enriched with quaternary ammonium dimethyl-hexadecyl-methacryloxyethyl-ammonium iodide (DHMAI; Figure 6) and methacryloyl ethoxylphosphorylcholine (MPC). The study showed that using 7.5% DHMAI improved the conversion rate of the composite and provided a strong antibacterial effect with a reduction in CFUs (colony-forming units) and metabolic activity while maintaining acceptable mechanical properties.