Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol Sol-gel derived fluoridated and non-fluoridated bioactive glass ceramics- based dental adhesives: Compositional effect on re-mineralization around orthodontic brackets Hira Firzok a , Saba Zahid b , Saad Asad c , Faisal Manzoor b , Abdul Samad Khan d, ⁎ , Asma Tufail Shah b a Department of Orthodontics, University College of Dentistry, The University of Lahore, Lahore, Pakistan b Interdisciplinary Research Centre in Biomedical Materials, COMSATS University Islamabad, Lahore Campus, Lahore 54000, Pakistan c Department of Orthodontics, Watim Dental College, Rawalpindi 44000, Pakistan d Department of Restorative Dental Sciences, College of Dentistry, Imam Abdulrahman Bin Faisal University, Dammam 31441, Saudi Arabia 1. Introduction Orthodontic treatment aims to achieve optimal function and ideal esthetics, yet not all outcomes of the treatment may be desirable, one of them is the formation of “white spot lesions” (WSLs). WSLs being the initial factual manifestations of dental caries can negatively impact dental esthetics and vitality of the tooth [1,2]. Many factors contribute to the occurrence of WSLs during orthodontic treatment such as in- adequate oral hygiene and presence of orthodontic appliances [3]. Both factors contribute to plaque accumulation on tooth surfaces [4], sub- sequently leading to a rapid increase in bacterial micro-flora that re- duces the pH at the plaque/enamel interface [5]. The reduction in pH can cause phosphate and calcium ions to escape from enamel [6]. Thus patients with full orthodontic appliances have a faster rate of progres- sion of caries [7]. Enamel re-mineralization is a naturally occurring repair process for non-cavitated lesions wherein calcium, phosphate, and fluoride ions are diffused back into the enamel, restoring the partially dissolved surface [8]. Re-mineralization is favored by using various agents such as casein phosphopeptide-amorphous calcium phosphate (CPP-ACP), calcium sodium phosphosilicate and amorphous calcium phosphate [9–11]. Fluoride containing resin-based composites (RBC) and glass ionomer cements (GIC) are also being used for orthodontic brackets to minimize the risks of demineralization [12]. Bioactive glasses (BG) are well-established bioceramics with the ability to release calcium, phosphorus, and silicon ions when exposed to saliva and eventually binds to the tooth surface. The BG has gained interest in modern dentistry and it has been used for clinical applica- tions such as sealing the root canal, regenerating the alveolar bone, and treating dentinal hypersensitivity [13]. The BG forms a hydro- xycarbonate apatite (HCA) layer, which is the main component of en- amel and dentin, contributing to enamel re-mineralization [9,10]. The addition of bioactive glass ceramics to resin-based composites (RBC) has proved to be a stepping-stone towards re-mineralization of sub- surface enamel lesions [12,14]. Incorporating fluoride into BG (F-BG with 5% fluoride) have been found to minimize decalcification around orthodontic brackets by forming fluorohydroxyapatite (FHAp), which is more acid resistant than HCA, therefore is of interest particularly for dental applications [15,16]. These F-BG containing adhesives have the potential to release F, Ca, and PO 4 for a prolonged period even under low pH environment, thus promoting re-mineralization. These F-BGs were prepared by con- ventional quench melt derived method, which is a high temperature (1100–1300 °C) synthetic route [17]. In this study, two types of bioactive glasses ceramics nanoparticles, BGC-1 and BGC-2, have been used and compared with similar compo- sitions with fluoride ions; F-BGC-1 and F-BGC-2. The BGC-1/F-BGC-1 and BGC-2/F-BGC-2 have been prepared by using two different sources of calcium oxide (CaO) i.e. calcium hydroxide [Ca(OH) 2 )] and calcium nitrate tetrahydrate [(Ca(NO 3 ) 2 .4H 2 O], respectively. In our previous studies [18], these two precursors have been studied and the results showed that Ca(OH) 2 ) enhanced the mechanical strength of bioactive glass. In present study, these precursors have been used to prepare bioactive glass with and without fluoride. F-BGC-1 and F-BGC-2 were selected to investigate the role of fluoride in re-mineralization. Wong et al. [17] incorporated F-BG (prepared by quench melt method) into a resin and found that fluoride-containing BG adhesive raises pH of system and protects the enamel. However, no morphological studies were performed during this study. Sol-gel method has shown its en- ormous potential in biomedical applications as an advantageous method for the production of bioactive glasses [19]. Therefore, in this current study, the authors prepared BGC and F-BGC by simple sol-gel method, which is a room temperature synthesis, in contrast to quench melt derived method, and studied their effect by structural and mor- phological analysis and topography. The hypothesis was that the F-BGC based adhesive could provide better re-mineralization potential than https://doi.org/10.1016/j.jnoncrysol.2019.119469 Received 13 April 2019; Received in revised form 15 May 2019; Accepted 28 May 2019 ⁎ Corresponding author at: Department of Restorative Dental Sciences, College of Dentistry, Imam Abdulrahman Bin Faisal University, Dammam 31441, Saudi Arabia. E-mail address: akhan@iau.edu.sa (A.S. Khan). Journal of Non-Crystalline Solids 521 (2019) 119469 0022-3093/ © 2019 Elsevier B.V. All rights reserved. T