Translucent High-Strength and Thermally Compatible Glass-Ceramics for PFM Applications.
Objectives: To synthesise new translucent leucite glass-ceramics for veneering metal substrates, with matched CTE, high strength and reliability. Methods: Two Commercial aluminosilicate glasses (G, Cera Dynamics/UK) were designed using Appen factors and synthesised using melt/quench methods at 1550°C for 5 h and provided as ground powders. Glass 1 was crystalised (GC) using a two-step heat treatment (10°C /min to 592°C/1 hour, then 1040°C/30 mins) then ball milled (125 μm). Weighed ratios of GC (10-50 wt.%) were dispersed into glass 2 to produce GC/G groups. The 1:1 G/GC mixture was compacted and then vacuum sintered (1040°C, 2 mins) to produce discs (G/GC1, n=20). Optimised samples were pre-sintered in a burnout furnace (1040°C, 30 mins) then milled using industrially (G/GCA) or in house (G/GCB) milling, then vacuum sintered (n=20 per test group). Test groups were lapped to 1000 grit and Biaxial Flexural Strength (BFS) tested (crosshead speed=1mm/min) against commercial GCs (IPS Style Ceram [ISC] and IPS InLine [IiL]). The glasses and G/GC groups were characterised using dilatometry, SEM and XRD. Results: XRD revealed an amorphous phase for the glasses (1, 2) before and after firing. Tetragonal leucite was found for all G/GC and commercial groups. The CTE of the G/GC groups was 9.2-14.4 x10−6 K−1 (100-400 °C), with GC addition correlated with CTE (r2=0.97). SEM indicated domains of fine leucite crystals distributed in the glassy matrix. Mean BFS was significantly higher for G/GCA compared to the other test groups (p<0.05). G/GCA had a higher Weibull m value compared to ISC (p<0.05), and higher characteristic strength than ISC and IiL. G/GCA and G/GCB were highly translucent. IiL had a significantly lower Mean BFS and characteristic strength compared with the other test groups (p<0.05). Conclusions: Synthesis of new high strength, thermally compatible and translucent GC were achieved for PFM applications, with the potential for low wear.