SCIENTIFIC ARTICLE Australian Dental Journal 2011; 56: 193–200 doi: 10.1111/j.1834-7819.2011.01323.x Prevention of enamel demineralization after tooth bleaching by bioactive glass incorporated into toothpaste E Gjorgievska,* JW Nicholson  *Faculty of Dental Medicine, Department of Paediatric and Preventive Dentistry, University ‘Ss Cyril and Methodius’ Skopje, Macedonia.  School of Science, University of Greenwich, Medway, United Kingdom. ABSTRACT Background: The aim of this study was to determine the effects of bleaching on the structure of the enamel layer of teeth and the potential of the commercial bioactive glass NovaMinÒ in two different toothpastes to remineralize such regions of the enamel. Three aspects were considered: the extent and nature of the alterations in the enamel after application of the bleaching agents; the extent of remineralization after application of two commercial toothpastes containing bioactive glass; and whether or not there were differences between the toothpastes in terms of their effectiveness in promoting remineralization. Methods: Bleaching agent based on 16% carbamide peroxide was applied to the enamel surface of freshly extracted human molars for 8 minutes, once a day for 7 days. After the bleaching cycles, the enamel surface was analysed by SEM and EDX. Results: The results obtained in the study lead to the conclusion that application of 16% carbamide peroxide causes distinct morphological changes to the enamel surface which vary from mild to severe. Subsequent treatment with either of the toothpastes containing the bioactive glass NovaMinÒ resulted in the formation of a protective layer on the enamel surface, consisting of bioactive glass deposits, with only slight differences between the two brands. Application of these dentifrices also caused increases in the Ca and P content of the enamel layer, returning it to that of undamaged enamel. Conclusions: Remineralizing toothpastes should be used after bleaching, in order to repair any damage to the mineral tissue caused by these procedures. Keywords: Bioactive glass, bleaching, demineralization, enamel, remineralization. Abbreviations and acronyms: CP = carbamide peroxide; HP = hydrogen peroxide. (Accepted for publication 29 August 2010.) INTRODUCTION Bleaching has become a popular procedure with patients seeking improvements in the perceived appear- ance of their teeth. Generally, bleaching agents are based on either hydrogen peroxide (HP) or carbamide peroxide (CP). Their activity leads to improvement of the discoloured tooth structure through decomposition of peroxide into free radicals 1 which break down large pigmented molecules. It is the chromophores within these large molecules which absorb light in the visible region, and are thus responsible for the colour stain in the enamel. Fragmentation of these molecules into smaller species by free radicals alters the light absorp- tion and thus reduces or eliminates the stain. 2 Carbamide peroxide is a chemical adduct of urea and HP, which upon dissolving in water or saliva dissociates back into HP and urea. Thus, CP can be considered as a precursor of the active bleaching species HP. 1–4 Although the bleaching treatment offers aesthetic improvement, the effect of bleaching agents on dental hard tissues is still being debated. Some studies have claimed that there are no significant effects of bleaching agents on human enamel. 5 However, other studies have obtained contrary results, with treated enamel showing morphological changes suggesting that bleaching is an erosive process. 6–9 Bleaching directly affects the organic (protein) content of the tooth, but this leads to changes in the mineral phase, resulting in the observed morphological changes to the tooth surface. 10 It may be possible to reverse this damage by the deployment of mineralizing agents to treat the affected tooth surface. One type of mineralizing agents are the bioactive glasses. These materials are capable of bonding chemically to hard dental tissues and their components are oxides of calcium, sodium, phosphorus and silica in ratios that impart bioactivity. In vivo, these ª 2011 Australian Dental Association 193 Australian Dental Journal The official journal of the Australian Dental Association