Development of CAD-CAM Leucite Glass-Ceramics for Dentistry

Objectives: To evaluate the microstructure, solubility, machinability, and colour dispersion of novel leucite glass-ceramics
Methods: An aluminosilicate glass was synthesised using melt/quench methods at 1550°C for 5h. The milled glass was crystalised using a two-step heat treatment (10°C/min to 592°C/1 hour, then 1040°C/30 mins and quenched. The glass-ceramic (GC) frit was crushed/ ball milled (1h) and screened (125 μm sieve).
The GC powder was mixed with and without an experimental colour frit and modelling liquid (Build-up, Ivoclar-Vivadent) followed by powder compaction (1 bar/1 min) in a steel mould with plunger. Specimens were sintered in a porcelain furnace (Multimat MCII, Weybridge, UK) at 1040°C for 2 mins under partial vacuum. Sintered specimens were evaluated using UV-Vis and compared with a Vita shade guide using a colour corrected light. Solubility was evaluated on the uncoloured GC using ISO 6872:2008. Sintered GC ingots were used to produce heat pressed glass-ceramic blocks (15 x12 x10mm) using a press furnace (EP3000, Ivoclar-Vivadent). The GG was characterised using SEM and TEM-EDX.
Brass dies were scanned, and a standardised premolar crown designed. GC blocks attached to spindles and an STL crown file were used to mill the crowns using a milling machine (inLab, MCx5, Sirona, Germany). Marginal fit was evaluated at 10 equidistant locations at the crown margins using light microscopy (Keyence, UK) and SEM.
Results: SEM/STEM-EDX revealed crystal/residual glass ratios and fine (Mean (SD)) crystals 0.62 (0.42) μm², enabling a Mean (SD) marginal crown fit of 30.1 (4.2) um. ISO Solubility results were 38.3 μg/cm²_. Addition of colour frit allowed graduated changes in transmittance in the GC and a good shade match.
Conclusions: CAD-CAM of novel leucite GCs demonstrated good marginal fit, low solubility and controlled dispersion of colour. These glass-ceramics save processing time as additional heat treatments following machining are avoided.