Compendium of Continuing Education in Dentistry

Through dental procedures and environment, periodontal tissues are exposed to many types of reactive oxygen species (ROS). Recently, various forms of antioxidants have been introduced as an approach to fight dental diseases and improve general gingival health. This article focuses on the classification of antioxidants and the link between oxidative stress and periodontal disease. The protective mechanisms of antioxidants and how routine dental procedures may increase ROS is discussed. The final section reviews the effect of tobacco products on gingival health and disease. An antioxidant is any substance that significantly delays or prevents oxidation of an oxidizable substrate1 (Figure 1) . Antioxidants are classified by five methods: mode of function, location of action, solubility, structural dependence, and origin and source. Each method is summarized in Table 1.2 The physiologic and pathologic changes in the human body depend on free radical (FR) and reactive oxygen species (ROS) interactions (Figure 2 and Figure 3) to maintain normal cellular activities.3 In aerobic organisms, the imbalance between ROS generation and antioxidant levels leads to increased oxidative stress and cellular degeneration (Figure 3 ). Antioxidants can counter the formation of free radicals (Figure 4 and Figure 5) and prevent free radical damage by donating electrons. The involvement of ROS and the antioxidant defense mechanisms in human saliva has been demonstrated in various processes of the oral cavity: healing periodontal disease, preventing oral carcinogenesis, reducing oral mucosa inflammatory reactions, and ameliorating metal-based restoration reactions.4 The salivary antioxidant system has an essential anticarcinogenic role in the oral cavity, aimed at fighting ROS and reactive nitrogen species (RNS) caused by smoking, alcoholic beverages, food, carbonated drinks, dental restorations and/or various other volatile sources freely entering the oral cavity through the body's largest open gate—the mouth (Figure 6).5 The salivary antioxidant system includes various molecules and enzymes. The most important are the uric acid molecule and the peroxidase enzyme; both are water-soluble. Uric acid contributes approximately 70% of the total salivary antioxidant capacity.6 An animal model showed the anticarcinogenic capability of saliva significantly inhibits the initiation and progression of oral cancer.7 In a study using the Ames test, saliva inhibited the mutagenicity of oral cancer inducers: cigarette smoke and 4-nitroquinoline 1oxide (4NQ0).8 Saliva also plays an important role in preventing cigarette-induced deoxyribonucleic acid (DNA) damage.9 This antioxidant capacity of saliva protects against oral cancers.10 However, in cases of periodontal disease formation and progression when normal cellular mechanisms are hampered, the oxidation process occurs due to an increased ROS production induced by other etiologic factors of periodontitis, such as bacterial plaque formation./p> Bacterial plaque is the most important substrate in periodontal disease development. A study of dental plaque bacteria has implicated its role in inducing "oxygen shock" to activate free radicals and the collagen-destroying enzymes. The process of collagen matrix degradation affects not only the amount of bone destruction and rate of inflammation but also the free radical damage, Figure 1