Remineralization of Demineralized Enamel by Toothpastes: A Scanning Electron Microscopy, Energy Dispersive X-Ray Analysis, and Three-Dimensional Stereo-Micrographic Study Elizabeta S. Gjorgievska, 1, * John W. Nicholson, 2 Ian J. Slipper, 3 and Marija M. Stevanovic 1 1 Faculty of Dental Medicine, University “Sts Cyril and Methodius” Skopje, Republic of Macedonia 2 St Mary’s University College, Twickenham, London, UK 3 School of Science, University of Greenwich, Chatham, Kent, UK Abstract: Remineralization of hard dental tissues is thought to be a tool that could close the gap between prevention and surgical procedures in clinical dentistry. The purpose of this study was to examine the remineralizing potential of different toothpaste formulations: toothpastes containing bioactive glass, hydroxy- apatite, or strontium acetate with fluoride, when applied to demineralized enamel. Results obtained by scanning electron microscopy ~SEM! and SEM/energy dispersive X-ray analyses proved that the hydroxyapatite and bioactive glass-containing toothpastes were highly efficient in promoting enamel remineralization by formation of deposits and a protective layer on the surface of the demineralized enamel, whereas the toothpaste containing 8% strontium acetate and 1040 ppm fluoride as NaF had little, if any, remineralization potential. In conclusion, the treatment of demineralized teeth with toothpastes containing hydroxyapatite or bioactive glass resulted in repair of the damaged tissue. Key words: remineralization, demineralization, bioactive glass, hydroxyapatite, strontium acetate, fluoride I NTRODUCTION The mineral phase in dentine and enamel is a mixture of compounds, including a number of carbonated apatites, with greater diversity of composition in dentine than in enamel ~Elliott, 1997!. Mineral loss ~demineralization! and gain ~re- mineralization! by enamel are dynamic physicochemical pro- cesses that are in balance in a healthy mouth under most circumstances. However, when oral bacteria form a biofilm on the enamel surface ~plaque! and this biofilm is exposed to fermentable dietary carbohydrates ~Paes Leme et al., 2004!, there is a drop in pH due to the formation of organic acids, mainly lactic acid, as a result of metabolic activity of the biofilm. If the low pH is maintained for a certain time, the mineral phase dissolves to an extent, leading to the predom- inance of demineralization. When exposure to carbohy- drates ceases, pH gradually rises, and supersaturating conditions are restored leading to a certain amount of re- placement of the mineral phase ~Sheiham, 2006!. Under physiological conditions, oral fluids ~saliva, bio- film fluid! have calcium ~Ca! and phosphate ~P! in supersat- urated concentrations with respect to the mineral phase of enamel, and as a result, calcium and phosphate ions are continually deposited on the enamel surface or are redepos- ited in enamel areas where they were lost. This can be considered a natural defense mechanism promoted by saliva to preserve the mineral structure of enamel in the mouth ~Reynolds, 2008!. Because of the chemical inhomogeneity of enamel, the process of enamel remineralization is rather complex. Calcium availability remains the main limiting factor in enamel remineralization ~Walsh, 2009!. Enamel remineralization has been studied for about 100 years, and it has been suggested that “the non-invasive treatment of early caries lesions by remineralization has the potential to be the major advance in the clinical management of the disease” ~Reynolds, 2008, p. 74!. The possibility of reminer- alization of hard dental tissues could close the gap between prevention and surgical procedures in clinical dentistry ~Pradeep & Prasanna, 2011!. Fluoride remains the best established agent to promote remineralization.Trace amounts of fluoride in saliva are effec- tive in shifting the balance from demineralization to reminer- alization. This is attributed to fluoride-enhanced precipitation of calcium phosphates and formation of fluorhydroxyapatite in dental tissues ~ten Cate & Featherstone, 1991; ten Cate, 1999!. Fluorapatite is less soluble in acid solutions than hy- droxyapatite, which in turn is less soluble than carbonated apatites ~Shellis et al., 1993; Shellis & Wilson, 2004!. Apart from fluoride, there are several materials that can be used to promote remineralization. The clinical effective- ness of these agents depends on several challenges, as shown in Table 1 ~Zero, 2006!. One possible remineralization material is bioactive glass, developed by Hench in the late 1960s ~Hench et al., 1972!. Due to its high bioactivity, bioactive glass has several appli- cations in dentistry: for example, in rehabilitation of the dentoalveolar complex ~Wilson et al., 1994! and in regener- ation of periodontal bone support ~Lovelace et al., 1998!. Recently, it has been incorporated into toothpastes, as a mineralizing agent for prevention of tooth decay, as well as Received January 8, 2013; accepted February 5, 2013 *Corresponding author. E-mail: egjorgievska@stomfak.ukim.edu.mk Microsc. Microanal. Page 1 of 9 doi:10.1017/S1431927613000391 Microscopy AND Microanalysis © MICROSCOPY SOCIETY OF AMERICA 2013