Please use this identifier to cite or link to this item: https://hdl.handle.net/2440/122143
Type: Thesis
Title: The ability of thiourea to scavenge hydrogen peroxide and hydroxyl radials during the intra-coronal bleaching of blood-stained root-filled teeth
Author: Farmer, Daniel Swithin
Issue Date: 2000
School/Discipline: School of Dentistry
Abstract: The intra-coronal bleaching of root-filled teeth has been described in the literature for over 100 years. Currently the two most common bleaching techniques utilise hydrogen peroxide. The method described in the literature in 1963 by Nutting and Poe relied on the inherent instability of the hydrogen peroxide to decompose into its oxidising components which were capable of penetrating into the stained tooth structure and bleaching the stained dentine. This method has become known as the ,,walking bleach" technique. The application of heat to activate the hydrogen peroxide has been used since the nineteenth century. In 1965, Stewart termed this method involving the application of heat the "thermocatalytic bleaching" technique' Harrington and Natkin (lg7g) first reported the association between the use of hydrogen peroxide in the bleaching of traumatised teeth which had been root-filled and a form of extemal root resorption. Since that report there have been numerous case reports of a similar association and several theories have been postulated as to the cause of this resotptive process. Marin et al. (1997) demonstrated that the staining of the traumatised tooth with blood was the result of the rupture of red blood cells within the pulp tissue and the release of haemoglobin and haem moieties which pass into the dentinal tubules and cause the resultant discolouration. Hydrogen peroxide is capable of reacting with available iron found associated with haemoglobin within the dentine tubules to produce hydroxyl radicals. Both hydrogen peroxide and hydroxyl radicals are capable of damaging cells and tissues of the periodontal ligament. This destruction may result in aÍL inflammatory response which could be responsible for the initiation of the resorption process. Dahlstrom et al. (1997) reported on the ability of hydroxyl radicals to be generated on the outer surface of the tooth that had been stained with blood and thermocatalytically bleached. Dahlstrom et al., in the same study, detected hydrogen peroxide on the outer surface of the tooth in a small percentage of his samples' This latter finding was in agreement with the findings of Rotstein et al' (1991) who had previously reported the detection of hydrogen peroxide on the outer surface of teeth which had been stained with blood and intra-coronally bleached' Thiourea has been used in the textile industry for many years as a reductive bleaching agent to bleach wool and paper. It has also been used in the medical profession for a number of years to scavenge hydroxyl radicals and a number of other oxygen derived free radicals during the reperfusion of various organs and in the treatment of various clisease states. Maroulis (lgg4) showed that the introduction of thiourea into the intracoronal bleaching of root-filled teeth had no detrimental effect on the bleaching effrcacy of hydrogen Peroxide. The aim of the present research was to (1) Compare the quantity of hydrogen peroxide and the quantity of hydroxyl radicals present on the outer root surface of blood stained teeth which have been intra-coronally bleached with either hydrogen peroxide sealed into the pulp chamber ( "walking" bleach), or with hydrogen peroxide which has been activated with heat ("thermocat al5rúc" bleach) and (2) Determine the ability of thiourea to scavenge hydrogen peroxide and hydroxyl radicals within radicular dentine structure during the intra-coronal bleaching of blood-stained, rootfilled teeth. Thirty-five extracted, single rooted premolar teeth were stripped of their periodontal ligaments and the pulp tissue extirpated. Thirty of these teeth were stained with blood using a method devised by Marin et al. (1997). The teeth were obturated with AH26 and gutta percha and bleached with hydrogen peroxide, with or without the application of heat. Thiourea was introduced into the bleaching protocol in various groups. The teeth were suspended in a bath of salicylate and the products of the reaction between hydroxyl radicals and the salicylate were detected using high performance liquid chromatography (HPLC) and electro-chemical detection (ECD). Twenty-two of the 35 teeth sampled generated reaction products of the hydroxylation of salicylate. There was no statistically significant difference between the quantity of hydroxyl radicals generated between the two methods of intra-coronal bleaching. Greater yields of hydrogen peroxide were detected on the outer surface of the teeth which had been bleached with the "walking" bleach technique. The presence of thiourea in the bleaching protocol resulted in a statistically significant decrease in the amount of hydrogen peroxide and hydroxyl radicals detectable on the outer surface of the tooth. There was a statistically significant decrease in the amount of thiourea that was detected on the outer surface of the tooth when hydrogen peroxide was combined with thiourea, compated to the introduction of thiourea alone into the pulp chamber. It was concluded from this research that both methods of intra-coronal bleaching of root-filled teeth are capable of generating hydroxyl radicals which are detectable on the outer surface of the tooth. Hydrogen peroxide is capable of diffusing from the pulp chamber to the outer surface of the tooth, although the activation of the hydrogen peroxide with heat resulted in lesser quantities being detected on the outer surface of the teeth. There was a positive association between the presence of thiourea and a decrease in the detection of hydrogen peroxide and hydroxyl radieals. If hydroxyl radicals and hydrogen peroxide are, in part, tesponsible for the initial activation of clastic cells involved in invasive cervical resorption, then the introduction of thiourea into the bleaching protocol may provide a method of preventing the initiation of the resorption process.
Dissertation Note: Thesis (M.D.S.)--University of Adelaide, Dental School, 2001
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