Synthesis and Optimisation of Diopside Glass-Ceramics for Dentistry and Biomedical Applications.

Abstract

Aim: To synthesise new high strength Diopside glass-ceramics based on diopside solid solution system, that would be thermally compatible with yttria-stabilised zirconia polycrystalline (YTZP) substrates. This may address YTZP clinical failure rates, due to failure of the veneering material.

Methods: A series of experimental glasses were designed using an Appen model and synthesised using melt quench methods. Glasses were then ball milled to achieve different particle sizes (<125 and <45 microns). The glasses were characterised using X-ray diffraction (XRD), dilatometry and differential scanning calorimetry (DSC) to find optimised nucleation curves. Two-step heat treatments were carried out for the glasses to make Diopside glass- ceramics. Glasses and Diopside glass-ceramics were characterised using secondary electron imaging (SEI), magic angle spinning nuclear magnetic resonance (MAS-NMR) and XRD. Optimised Diopside glass-ceramic (group 1) and IPS e.max Ceram (group 2) were veneered onto YTZP substrates to form bilayered specimen groups (n=30 per test group). The biaxial flexural strength (BFS) of the experimental Diopside glass-ceramics, IPS e.max Ceram ceramic and the bilayer specimen groups were tested using the ball on ring test at a crosshead speed of 1mm per minute.

Results: XRD revealed that all glasses synthesised were amorphous, while glass-ceramics showed a major Diopside crystal phase and some formulations albite and wollastonite as minor phases. Dilatometry showed thermal expansion coefficients (CTE) ranging from 8.40-10.99 3 x10-6/k which was within the range thermally compatible with YTZP (10.86x10-6). DSC showed sharp nucleation peaks with little shift in crystallisation peaks for glasses at different particle size, suggesting bulk crystallisation. SEM of the glasses showed homogenously distributed spherical domains, while the glass-ceramic indicated dendritic, elongated diopside crystals and an interconnected unique microstructure with no microcracking present in the glassy matrix. MAS-NMR of 27Al of the diopside glass-ceramics showed two broad peaks, the major corresponding to tetrahedral aluminium (Al) and the other peak corresponding to octahedral aluminium (Al), which suggested the presence of a solid solution. Diopside glass-ceramics resulted in a high BFS (152.8 -196.7 MPa) which was significantly (p<0.05) higher compared to commercially available material IPS e.max Ceram (103.2 MPa). The BFS of experimental diopside glass-ceramic veneered onto YTZP showed high BFS (510.1MPa) which had a significantly higher (p<0.05) BFS when compared with IPS e.max Ceram veneered onto YTZP (324.7 MPa).

Conclusions: A range of high strength (152.8 -196.7 MPa) diopside glass-ceramics were synthesised which were thermally compatible (8.40-10.99-x10-6/k) with YTZP. When veneered onto YTZP they produced a high BFS (510.1 MPa) that might help to reduce or preventing chipping failure rates encountered in veneered YTZP restorations.