Characterization and In Vitro Bioactivity Study of Ternary Glass-ceramic Coatings

ABSTRACTThe aim of the present study was to test the in vitro bioactive behavior of two new ternary mixtures consisting of a glass-ceramic porcelain, a bioactive glass and alumina (PBA) as coatings on dental glass ceramic substrates. They consisted of bioactive glass- in the system SiO2-Na2O-CaO-P2O5−, powder from a leucite-fluorapatite glass ceramic and γ-Al2O3 in 50-42.5-7.5 wt % respectively, while coatings with the same two components in 50-50 wt % ratio, without Al2O3, served as control. The characterization of the coatings was performed by Scanning Microscopy (SEM-EDS), Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD). The in vitro bioactivity was tested in Simulated Body Fluid (SBF) and the surfaces of reacted specimens were examined by SEM and FTIR. All coatings presented rough surface, while FTIR spectra revealed the characteristic peaks of the crystallized phases in the bioactive glass network and dental glass ceramic, i.e. Sodium Calcium Silicate (Na4Ca4Si6O18), Leucite (KAlSi2O6) and Fluorapatite (Ca5(PO4)3F), and furthermore the very limited participation of Al3+ in the bioactive glass network. In the coatings the main phases detected by XRD were, also, Na4Ca4Si6O18 and Leucite, dispersed in an amorphous glassy matrix. Furthermore, a transformation of γ-Al2O3 to δ-Al2O3 was observed and a new phase of Nepheline (Na7.15Al7.2Si8.8O32) was detected in traces. Apatite was developed sporadically on the surfaces of the PBA coatings after 30 days in SBF. These results demonstrate a slight retardation of bioactive response of the coatings of the ternary mixtures compared to dual ones consisting of dental glass ceramic and bioactive glass. The incorporation of Al2O3 can enhance the mechanical properties without a substantial degradation of bioactivity. This finding renders these coatings as promising composite materials for potential dental applications.