HYDROXYL RADICAL ACTIVITY IN THERMO-CATALYTICALLY BLEACHED ROOT-FILLED TEETH

Intra-coronal bleaching of root-filled teeth has been associated with invasive cervical root resorption. It is considered that during bleach ing hydrogen peroxide diffuses through the tooth structure into the ce rvical periodontium, resulting in periodontal tissue destruction and i nitiating a resorptive process. Hydrogen peroxide is capable of genera ting hydroxyl radical, an oxygen-derived free radical, in the presence of ferrous salts. Hydroxyl radicals are extremely reactive and have b een shown to degrade components of connective tissue, particularly col lagen and hyaluronic acid. The aim of the present study was to determi ne whether hydroxyl radicals are generated during the bleaching of roo t-filled teeth which have been discoloured by blood. Forty extracted h uman premolar teeth were root-filled with gutta-percha and AH26 sealer cement. Twenty of the teeth were experimentally discoloured by blood. All teeth were then thermo-catalytically bleached using 30% hydrogen peroxide while tooth roots were seated in a test solution of sodium sa licylate. Hydroxyl radical generation was determined by the detection of reaction products of this radical with salicylate using high perfor mance liquid chromatography with electrochemical detection (HPLC-ECD). The presence of hydroxyl radicals was detected in twenty-five of the teeth. There was a significant association between the production of h ydroxyl radicals and the presence of tooth discolouration caused by bl ood components. Greatest yields of hydroxyl radicals occurred in teeth in which EDTA had been used to clean the pulp chamber prior to bleach ing. It was concluded that hydroxyl radicals are generated during the thermocatalytic bleaching of root-filled teeth. Generation of this tox ic chemical species may be one mechanism underlying periodontal tissue destruction and root resorption after intra-coronal bleaching.