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.