Abstract: PURPOSE: To explore the correlation and mechanism of oxidative stress (OS) in the co-morbidity of chronic periodontitis (CP) and metabolic dysfunction-associated steatotic liver disease (MASLD). METHODS: A total of 162 patients who visited the Fourth Affiliated Hospital of Anhui Medical University from September 2024 to February 2025 were selected and divided into the simple CP group (n=42), the simple MASLD group (n=41), the comorbid group (n=39) and the healthy group (n=40). The salivary malondialdehyde (MDA), superoxide dismutase (SOD), periodontal depth (PD), attachment loss (AL) and liver stiffness measurement (LSM) of each group were detected, and statistical analysis was carried out. Results: In terms of periodontal indicators, the PD and AL values of patients in the comorbid group were significantly higher than that of the simple CP group (P< 0.05). In addition, the PD and AL values of the comorbid group and the simple CP group were significantly higher than those of the healthy group and the simple MASLD group (P< 0.05). The OS indicators showed that the MDA level of saliva increased in the order of healthy people, simple CP group, simple MASLD group and comorbid group, while the SOD activity of saliva decreased in order, and the differences between the groups were statistically significant (P< 0.001). As an indicator of comprehensive OS evaluation, the saliva MDA/SOD ratio of the comorbid group was significantly higher than that of all other groups (P< 0.001). In patients with simple CP and simple MASLD, the disease severity and OS level showed a positive correlation, the MDA level and MDA/SOD ratio of the severe group were significantly higher than that of the mild-moderate group, while the SOD activity was significantly lower (P< 0.001). Through the analysis of the intermediary effect model (PROCESS Macro Model 4) based on the Bootstrap method, it was found that the MDA/SOD ratio plays a partial intermediary role in the relationship between PD and LSM, and its effect value was 0.359 kPa, which explained 37% of the total impact on liver injury. CONCLUSIONS: OS level is positively correlated with CP and MASLD and their severity, and in patients with CP and MASLD co-disease, the degree of OS imbalance shows a synergistic correlation with periodontal and liver injury indicators. As a test sample for non-invasive OS markers, saliva has good applicability and potential for application in co-morbidity screening and efficacy monitoring.

Key words: Oxidative stress, Chronic periodontitis, Metabolic dysfunction-associated steatotic liver disease, MDA, SOD