Free radicals are the molecules or molecular species containing one or more unpaired electrons with independence existence. Reactive Oxygen Species are constantly formed during normal cellular metabolism (lipid peroxidation) and due to various environmental influences (ionizing radiations). Free radicals are highly reactive, capable of damaging almost all type of bio-molecules, and have been implicated in the causation of many diseases including periodontitis. To mitigate the harmful effects of free radicals, the aerobic cells have developed antioxidant defense mechanism- enzymatic antioxidants (superoxide dismutase, catalase) and non-enzymatic antioxidants (Glutathione, selenium, α-tocopherol, β-carotene).