Apatite Growth on Bioactive Glass in Artificial Saliva
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Apatite Growth on Bioactive Glass in Artificial Saliva Sarah E. Efflandt, Robert F. Cook, Lorraine F. Francis Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, U.S.A. ABSTRACT Bioactive glass disks from the MgO-CaO-P2O5-SiO2 system were placed in artificial saliva for time periods varying from 1 to 42 days. Surfaces were then analyzed using scanning electron microscopy (SEM) and x-ray diffraction to investigate surface morphologies and crystallinity. SEM examination exhibited dramatic surface changes as early as 2 d. X-ray results showed crystallinity in the form of apatite at 10 d, which became more developed though 42 d. The bioactive glass in water and non-bioactive glass in artificial saliva were used as controls; both exhibited no evidence of apatite formation on their surfaces through the 42 d time period. This study shows that bioactive glass reacts in artificial saliva to form apatite and that the apatite layer becomes better crystallized over an extended time period. These results give a better understanding of the surface changes and mineralization that occur over time and can be used to interpret results from in vitro and in vivo studies done on bioactive glass in the oral environment. INTRODUCTION Apatite growth on bioactive glass materials has been shown to be an essential factor for biocompatibility and bonding to bone (1,2). Studies have also shown the promising use of these bioactive glass materials in dental implants that are in contact with bone (3-5). These bioactive materials may also have useful properties for other dental restorations such as fillings and crowns, in which the key interfaces are with dentin and saliva. The interaction between bioactive glasses and extracted human dentin was addressed in our previous studies, and showed encouraging results (6). The present study was designed to assess the interaction of bioactive glass from the MgO-CaO-P2O5-SiO2 system in artificial saliva. The formation of apatite on bioactive glasses in blood plasma is influenced by the fact that plasma is supersaturated with respect to apatite (7). Since saliva is also supersaturated with respect to apatite than blood plasma (8), it was our hypothesis that apatite would grow on bioactive glass in artificial saliva. This hypothesis was tested by placing bioactive glass in artificial saliva and then assessing surface and crystallinity changes over time. EXPERIMENTAL DETAILS Bioactive glass powder of composition 4.6MgO-44.9CaO-16.3P2O5-34.2SiO2 (wt%) was used in its as-received form from Specialty Glass, Inc. (Oldsmar, FL) to create amorphous glass disks. This glass composition is one developed by Kokubo et al for creating apatite-wollastonite glass ceramics (1). The powder was melted in a Pt crucible at 1500Û&IRUKDQGTXHQFKHG onto an Al block at room temperature. The resulting glass pieces were then annealed at 650Û& for 4 hours and ground to a flat surface using 240 grit and 400 grit SiC paper. The disks were LL2.5.1 Downloaded from http:/www.cambri
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