Flexural strength optimisation of a leucite reinforced glass ceramic.
OBJECTIVE
The aims of the study were to process a ceramic material with a fine leucite particle size using hot pressing techniques, to increase the flexural strength, reliability and ease of use.


METHODS
A starting glass composition of wt%; 64.2% SiO(2), 16.1% Al(2)O(3), 10.9% K(2)O, 4.3% Na(2)O, 1.7% CaO, 0.5% LiO and 0.4% TiO(2) was used to produce a leucite reinforced ceramic material. Twenty-one porcelain discs were produced by sintering the ceramic frit (group 1) and sixty-three discs by heat pressing the frit (groups 2, 3 and 4). Twenty-one Empress 1 ceramic discs were also heat pressed (group 5). Disc specimens were tested using the biaxial flexure test at a crosshead speed of 0.15mm/min and the data analysed using the Scheffé F multiple comparison test and Weibull statistics. Specimens were characterised using X-ray diffraction (XRD), secondary electron imaging and energy dispersive X-ray analysis where applicable.


RESULTS
The heat pressed groups (2, 3 and 4) had higher mean biaxial flexural strengths and characteristic strength values than groups 1 and 5 (p<0.05). XRD revealed the presence of tetragonal leucite in all test groups. Fine leucite crystals, tabular platelets and minimal matrix microcracking were found in the microstructure of test groups (1-4) with a more uniform leucite distribution in the heat pressed specimen groups (2, 3 and 4), which were associated with a significant increase in the biaxial flexural strength and reliability.


CONCLUSIONS
Optimisation of the microstructure by producing a fine microstructure and controlling the distribution via the correct pressing parameters may be extremely advantageous in these systems.
Cattell
M J
MJ
Department of Conservative Dentistry, St. Bartholomew's and The Royal London School of Medicine and Dentistry, QMW, Turner Street, London E1 2AD, UK. m.cattell@mds.qmw.ac.uk
Chadwick
T C
TC
Knowles
J C
JC
Clarke
R L
RL
Lynch
E
E
D000538:Aluminum Silicates / Q000737:chemistry*; D000704:Analysis of Variance; D002516:Ceramics / Q000737:chemistry; D003460:Crystallization; D018360:Crystallography, X-Ray; D003776:Dental Porcelain / Q000737:chemistry*; D004577:Electron Probe Microanalysis; D006358:Hot Temperature; D016018:Least-Squares Analysis; D016013:Likelihood Functions; D008422:Materials Testing; D010316:Particle Size; D018583:Pliability; D018709:Statistics, Nonparametric; D013674:Technology, Dental
D000538:Aluminum Silicates; D003776:Dental Porcelain; C078519:leucite; C023506:Glass ceramics