## 8 Periodontitis
These authors did not confirm the relationship between the salivary antioxidant defense system and parameters determining the clinical status of patients, but identified the relationship between antioxidant markers and bone-loss parameters in the saliva. [PERSON] et al. [117] observed that SOD activity and thiol antioxidant concentration significantly increased after treatment in the gingivitis and periodontitis group, which suggests a positive response to nonsurgical therapy. They also noticed that increased severity of periodontitis was associated with gradual decrease in antioxidant concentration. However, it should be noted that SOD activity as well as thiol concentration both before and after the applied nonsurgical treatment was lower in both mentioned groups than in the control group, and higher in the gingivitis group than in periodontitis, which indicates that antioxidant activity/concentration is evidently progressively decreasing from healthy subjects to patients with gingivitis and periodontitis. On the other hand, [PERSON] et al. [118] demonstrated significantly higher GR activity in the saliva of AgP and CP patients compared to the controls, and considerably higher in the saliva of AgP subjects vs. those with CP. The authors also observed a positive correlation between GR activity and PD and CAL as well as extent and severity of periodontal breakdown. Based on the performed analyses, the researchers assumed that ROS production results in increased GR activity, which is related to the inflammatory signaling pathway of periodontitis, as was confirmed by previously published papers [119; 115]. According to the authors, given that the aging process is accompanied by low-grade inflammation whose triggering mechanism is redox imbalance, aging could increase the degree of periodontal breakdown in a situation of increased GR activity. [PERSON] et al. [120] and [PERSON] et al. [121] showed higher activity of SOD, and [PERSON] et al. [122] higher activity of myeloperoxidase (MPO) in the saliva of CP patients vs. the control. The authors claimed that increased activity of these enzymes was related to periodontitis severity and oral health behaviors. According to [PERSON] et al. [120] and [PERSON] et al. [123], nonsurgical therapy (oral hygiene instruction, scaling and root surface debridement) seems to restore and control the antioxidant capacity by decreasing SOD activity, simultaneously increasing TAC and UA concentration as well as GPx activity to the level observed in the control group. It should be noted that SOD activity before the therapy was positively correlated with PD, CAL, GI, gingival bleeding index (GBI) and PI. Similar higher activity of manganese SOD (MnSOD), copper/zinc SOD (CuZnSOD) and CAT as well as positive correlations between the activity of the studied antioxidant enzymes (CAT, CuZnSOD) and clinical status parameters (BOP, PI, PD) of patients with periodontal disease were observed by [PERSON] et al. [124]. It should be highlighted that these results were obtained only in the early stage of the inflammatory response. Interestingly, the activity of CuZnSOD and CAT considerably increased with the percentage of sites with PD > 4 mm, whereas the relation between salivary activity of MnSOD and periodontal clinical parameters was nonsignificant. Melatonin shows a wide spectrum of activity, including osteopromotive, antioxidant, antiinflammatory and immunomodulating effects. It is even believed that melatonin can act as a potent antioxidant-enhancing mechanism that prevents periodontal disease [18]. In two studies, melatonin concentration was significantly lower in the saliva of periodontitis patients compared to healthy controls: by [PERSON] et al. [125] and [PERSON] et al. [126]; and in one study this relationship was not statistically relevant [18]. Interestingly, the study of [PERSON] et al. [125] revealed that elevated concentration of melatonin was related to healthy status or low inflammation (gingivitis) but not to periodontal destruction (periodontitis).