Purpose: This investigation was designed to determine whether heat pressing
and/or simulated heat treatments affect the flexure strength and microstru
cture of the lithium disilicate glass-ceramic of the IPS Empress 2 system.
Materials and Methods: Four groups of the lithium disilicate glass-ceramic
were prepared as follows: group 1 = as-received material; group 2 = heat-pr
essed material; group 3 = heat-pressed and simulated initial heat-treated m
aterial; and group 4 = heat-pressed and simulated heat-treated material wit
h full firings for a final restoration. Three-point bending tests and scann
ing electron microscopy (SEM) analysis were conducted. Results: The flexure
strength of group 2 was significantly higher than that of group 1. However
, there were no significant differences in strength among groups 2, 3, and
4, or between groups 1 and 4. The SEM micrographs of the lithium disilicate
glass-ceramic showed a closely packed, multidirectionally interlocking mic
rostructure of numerous lithium disilicate crystals protruding from the gla
ss matrix. The crystals in the glass matrix of the heat-pressed materials (
groups 2, 3, and 4) were a little more homogeneous and about 2 times bigger
than those of the as-received material (group 1). These changes of the mic
rostructure were greatest between groups 1 and 2. However, there were no ma
rked differences among groups 2, 3, and 3. Conclusion: Although there were
significant increases in the strength and some changes of the microstructur
e after the heat-pressing operation, the combination of heat pressing and s
imulated subsequent heat treatments did not produce an increase of strength
of IPS Empress 2 glass-ceramic.