The Impact of Sintering Temperature on the Bioactive Glass-Dental Porcelain Composite Material

Abstract

End temperature of the firing cycle, during processing of dental ceramics, directs the interaction of both sintering and crystallization pathways, tailoring physicochemical properties and bioactivity. Thus, the purpose of the present study was to investigate the influence of end temperature over the structural properties and composition, along with the bioactive behavior of dental porcelain, modified by bioactive glass. Sol-gel derived specimens of bioactive glass (58S)- commercial dental porcelain composites synthesized (BP) and underwent firing cycles at the crystallization temperature (Tc=1040oC) and the temperature just below the melting range (Tm=1080oC), as the composite material. The recommended temperature for the commercial porcelain (Ta=930oC) was examined, too. All specimens were characterized using X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM). The assessment of bioactivity was performed in vitro, via the detection of apatite layer development. The well-defined particles, observed by SEM, at 930oC, developed contact formation during the stage of neck growth at 1040oC and 1080oC, indicating the initiation of sintering process. Increasing temperature, the complex porei network became smoother, while spherical and closed porei were evident. FTIR revealed the predominance of wollastonite at the increased temperatures, along with the appearance of cristobalite, while XRD confirmed the results. Finally, the in vitro tests evidenced the bioactivity of the specimens independently of the final temperature, though the increased temperature caused delayed apatite layer formation on their surface. The, microstructural and chemical evolution of the studied composite is temperature-dependent. Increased temperature favored the sintering process initiation, along with the surface crystallization, which delays bioactivity.