Flexural strength of a nano-sized leucite glass ceramic

Methods: A starting experimental aluminosilicate (SG) glass powder was planetary milled (Pulverisette-P7, Fritsch, Germany) wet at 1000 rpm with 1mm YTZ for up to 240 mins (PM240). Powders from varying milling intervals were freeze dried and characterized using Particle Size Analysis. The starting glass was also attritor milled (1-S Lab, Union Process, USA) wet at 400 rpm with 5mm YTZ grinding media for 120 mins and 2 mm YTZ media for 120 mins (AM240). Powders (AM240, PM30, PM60, PM120, PM240 mins) were then subjected to crystallization heat treatments and characterised using Scanning Electron Microscopy and X-ray Diffraction. Image analysis software was used for crystal measurements on the photomicrographs. All specimen groups (PM120, PM240, AM240) were tested using the Biaxial Flexural Strength (BFS, ball-on-ring) test at a crosshead speed of 1mm/min (n=30). Commercial reference materials were also tested (Empress Esthetic [EE], Ceramco-3 [C3]). A one-Way-ANOVA was used for group comparisons.

Results: Tetragonal leucite was detected in all crystalline glass-ceramics. Glass milling and heat treatment produced a reduction in leucite crystal size: Median (Q1,Q3) PM30: 0.085 (0.055,0.127) µm² to PM240: 0.048 (0.030,0.070) µm². The leucite crystal number increased from 2.3 crystals/μm² (PM30) to 5.02 crystals/μm² (PM240). The mean BFS (SD) MPa of the test groups was: 255.0 (35.0) (PM120), 225.4 (41.8) (PM240), 165.5 (30.6) (EE), 75.1 (6.8) (C3) and 252.49 (38.7) (AM240). There was no significant difference in the mean BFS (p>0.05) between PM120 and AM240. All other groups were found to be significantly different (p<0.05) to each other.

Conclusion: A nanosized leucite glass-ceramic was synthesized which produced a higher flexural strength than the commercial materials.

Funding: St Barts and The London Charitable foundation, RAB05/PJ/06, State Scholarships Foundation, (IKY,Greece)