## 4 Discussion
As a result, the cell membrane will be disrupted, and cytoplasmic leakage will occur [17]. DMAHDM demonstrates more significant biofilm inhibition compared to other QAMs, such as dimethylaminododecyl methacrylate (DMADDM). This might contribute to the long alkyl chain within the DMAHDM structure, which may increase the monomer's contact surface, resulting in more pronounced inhibition. DMAHDM is co-polymerized with the resin matrix via a covalent bond with the polymer network made it immobilized in the composite [42,43]. This characteristic ensures that DMAHDM will constantly attain its antibacterial capability and not collapse over time [40], which was supported by our findings. Total microorganisms and total streptococci bacterial inhibition showed almost no difference between the baseline and water-aged composite samples. One exception was noticed with the 5% DMAHDM group, where there was about a 2-log difference in reduction on total microorganism in the water-aged samples. On the other hand, _Mutans streptococci_ showed less antibacterial effectiveness after aging than the baseline results. _Mutans_ is considered an indicative bacterium related to dental caries due to its capability in acid production, acid tolerance, and the synthesis of intracellular and extracellular polysaccharides [44]. The results suggest that aged samples were less effective against carigenic bacteria, as the baseline samples were more efficient in killing carigenic species. This could be attributed to the composite physical changes due to aging, allowing the carigenic species to adhere more efficiently to the surface than the smooth and non-altered baseline samples. Besides, the resin matrix's leaching may affect the distribution of the DMAHDM over the composite surface, which may compromise the contact killing against the cariogenic species. This explanation could be supported by the fact that DMAHDM has only one methacrylate side [45,46]. As a result, the cross-linking efficiency with other monomers might not be efficient such as dimethacrylate monomers. There were no significant differences between aged and baseline samples concerning metabolic activities and lactic acid reduction in this study. However, we noticed that the 5% DMAHDM and 5% DMAHDM-20% NACP composites revealed slightly higher metabolic activity after aging. Lactic acid production was also higher in those groups than the 3% DMAHDM-20% NACP compared to baseline samples. This outcome could be correlated to the physiological state of the viable bacterial cells. However, despite the slightly reduced effectiveness, the designed formulations demonstrated potent antibacterial effects following the aging process, indicating these formulations' capabilities to induce repeated antibacterial actions as more biofilm grown over the composite along the time. Although these formulations are promising candidates to prevent secondary caries development, their frequent use may raise questions regarding bacterial resistance. A previous study has addressed this question where the regular exposure to DMAHDM did not induce bacterial resistance against _S. mutans_ and other endodontic and periodontal pathogens [47]. It is of utmost importance to evaluate any new product's mechanical properties, predict its performance, and prevent catastrophic failures [48,49]. In dental composites, mechanical properties should be sufficient to function in the oral cavity for an extended period, hopefully encompassing the patient's lifetime [50]. The bioactive composites in this study demonstrated acceptable clinical performance compared to the commercially tested composite before aging. After one year of aging, the 3% DMAHDM, 5% DMAHDM, and 5% DMAHDM-20% NACP groups showed a significant reduction in flexural strength than their baselinecounterparts. However, the 3% DMAHDM composites showed a higher flexural strength value than the commercial control even after aging. The other groups did not show reduced values than the baseline measurement, but the reduction was not significant.