*3.1.7 Oxidative stress*

Periodontitis is an inflammatory disease of the supporting tissues of the teeth, it is defined as a complex infectious disease that results from the interaction of the

#### *Periodontal Disease - Diagnostic and Adjunctive Non-surgical Considerations*

bacterial infection and the response of the host to the bacterial challenge, and the disease is modified by environmental factors, acquired risk factors, and genetic susceptibility [21]. In recent years, the inflammatory response has been associated with oxidative stress, specifically with reactive oxygen species since it is considered to play a central role in the progression of many inflammatory diseases [22].

Oxidative stress create multiple products in affected tissues, such as reactive oxygen species which are free radicals and other non-radical derivatives which are involved in normal cell metabolism [23], other metabolites can damage DNA such as 8-hydroxy2′-deoxyguanosine (8-OHdG) or 8-oxo-7,8-dihydro-2′ deoxyguanosine (8-oxodG) which are two of the predominant forms of free radicals induced by oxidative lesions. In fact, 8-oxodG has been widely used as a biomarker for oxidative stress [24].
