## 4 Discussion  
Among dental diseases, the prevalence of periodontal disease increases progressively in adults over the age of 30, with reports indicating that 60-90% of individuals in their 40s and 50s are affected. Therefore, periodontal disease is the leading cause of tooth loss in adults, exposing the majority of individuals over 50 to the possibility of losing their teeth. Tooth loss leads to difficulties in food intake, resulting in a loss of health and ultimately a decline in quality of life [30]. To treat or manage periodontal disease, it is essential to control _P. gingivalis_, a primary causative bacterium of the condition. _P. gingivalis_ is an anaerobic bacterium primarily present during the active phases of chronic and aggressive  
Figure 4: Effects of various concentrations of _Lespedeza cuneata_ extract on cell morphology changes and proliferation inhibition of HGF cells cultured by SRB assay. Figure 3: Comparison of survival rates of HGF cells treated with _Lespedeza cuneata_ extract. * The significant difference among groups in one-way ANOVA. Different letters (a, b, c, d, and e) indicate the presented significant result of the post hoc Duncan test (_p_ < 0.05). periodontitis, and animal studies have shown that it causes ulceration and necrosis [31], forms phlegmonous abscesses, and activates splenic cells, promoting the bone resorption capabilities of osteoclasts [32]. As a method to inhibit this bacterium, antimicrobial agents, either topically or systemically, are sometimes used concurrently with non-surgical periodontal treatments to enhance their effectiveness. However, prolonged use of chemical antimicrobials can lead to resistance and an increase in pathogenic bacteria, prompting research into the clinical application of various natural substances with antimicrobial effects as alternatives [33]. Research based on natural materials has evaluated the antibacterial effect of green tea extract against _Prevotella intermedia_ (_P. intermedia_), a causative bacterium of periodontal disease [34]. Phytoncides have also been reported to cause structural morphological changes in _P. gingivalis_, demonstrating strong antimicrobial activity [30]. However, while research on the antibacterial potential of natural extracts is ongoing, appropriate assessments of safe concentrations through cytotoxicity evaluations have not yet been adequately conducted. In a study by [PERSON] et al., it was demonstrated that _Lespedeza cuneata_ extract had an antibacterial effect on _C. albicans_, a causative agent of oral mucosal disease [35], and _Streptococcus mutans_ (_S. mutans_), a causative agent of dental caries [36]. Therefore, this study aimed to evaluate the practicality of utilizing _Lespedeza cuneata_ extract as an effective and safe antimicrobial agent for periodontal disease by assessing its antibacterial effect against _P. gingivalis_, a representative periodontal bacterium, along with evaluating its toxicity on HGFs, which are normal cells present in periodontal tissue. The antibacterial effect of _Lespedeza cuneata_ was shown to be concentration-dependent, with CFU evaluation results indicating that higher concentrations of _Lespedeza cuneata_ extract led to greater antibacterial effects, demonstrating a 99.99% effectiveness at 5 mg/mL, and no detectable CFUs were observed at 40 mg/mL under the tested conditions. Although there have been no studies confirming the antibacterial effect of _Lespedeza cuneata_ extract on periodontal pathogens, research on _C. albicans_, a causative agent affecting oral mucosal diseases, reported complete bacterial eradication at a concentration of 30 mg/mL [35]. Additionally, studies involving _S. mutans_, the causative bacterium of dental caries, indicated a significant antibacterial effect at a concentration of 5 mg/mL, where no bacterial growth was observed [36]. In our study, when _Lespedeza cuneata_ extract was applied at 5 mg/mL against _P.