## 4 Discussion  
Various studies indicated that the expressions of hBDs, which play a role in the health of periodontal tissues and the maintenance of oral mucosal integrity, can be suppressed during the development and progression of cancer [1; 9; 30; 34; 38; 39; 40; 41]. The characterization of hBDs in the oral cavity is important in the presence of head and neck cancer that is directly or indirectly related to the oral region, as well as in disease therapeutic processes, such as radiotherapy with a local irritant effect. The present study is, to the best of our knowledge, the first one to investigate the relationship between hBD levels in oral fluids and radiotherapy in head and neck cancer cases. The prevalence of head and neck cancer in the general population is quite low; therefore, the number of participants was limited. Although a relatively small number of patients (\(n=16\)) were included in this study, all patients were followed up during and after radiotherapy, which is the main strength of the present study. A periodondually healthy control group was not included into the study design. Since periodontal status may have an effect on intraoral hBD levels, the clinical periodontal parameters of the patients were measured before treatment. Clinical periodontal parameters after radiotherapy were not included in this study since the study covered an average radiotherapy period of 6 weeks, which is a relatively short period of time for the significant progression of periodontal disease. A decreased salivary flow due to the radiotherapy process is frequently encountered in patients with head and neck cancer [42]. Gingival circular fluid, another intraoral fluid, can only provide information about the site of the tooth from which the sample is collected and its practically unsuitable for head and neck cancer patients due to its procedural difficulty. Therefore, considering the ease of application and standardization advantages, oral rinse analysis was preferred in our study. Upon examination of our study cohort, it is apparent that the participants utilize a plethora of medications based on their systemic conditions. There is a scarcity of research on the impact of these medications on human beta-defensin (hBD) secretion. According to the literature, specific medications may alter hBD levels. For instance, the utilization of metformin, a medication commonly used in diabetic circumstances, may enhance hBD  
Figure 2: Oral cavity hBD levels before radiotherapy, 1 st week of radiotherapy treatment, 3 rd week of radiotherapy treatment, 6 th week of radiotherapy treatment, and 1 month following the end of radiotherapy treatment *. (**a**) hBD-1, (**b**) hBD-2, (**c**) hBD-3. * Statistical differences in the hBD 1–3 levels between visits were analyzed with the Friedman test. The Wilcoxon signed-rank test was used for the post-hoc comparisons of the hBD-1 levels between each visit. As the Friedman test did not indicate any statistical difference for hBD-2 and hBD-3, pairwise analysis was not performed. expression [43]. Nevertheless, further studies are needed to comprehensively understand the influence of these and other medications on hBD secretion. In our study, a statistically significant increase in oral hBD-1 secretion was observed during the radiotherapy. It is an interesting finding that the hBD-1 secretion, which is generally stable and unaffected by inflammation [1, 8], increased during the radiotherapy. Although some studies have been conducted to examine the effects of radiation on hBD expression, studies directly examining the effects of radiation therapy on hBD expression are quite limited [44; 45; 46; 47]. [PERSON] et al. showed that radiation therapy applied to oral cancer patients reduced cutaneous hBD secretion [44]. In this study, the decrease in cutaneous hBD expression was interpreted as potentially increasing the risk of microbial infection [44].