Page 36 - CEREC Q4|2012

32 | cerecdoctors.com | quarter 2 | 2013
in-office cad/cam processing has
shortened the time required for dentists
to deliver fully functional and esthetic
restorations to their patients. Yet, despite
the reduced number of required office
visits, many clinicians still look for ways
to make the treatment and fabrication
processes more efficient without sacri-
ficing predictability.
Among the materials that can be
processed using in-office CAD/CAM tech-
niques is lithium disilicate (e.g., IPS e.max
CAD, Ivoclar Vivadent).1 Typically, lithium
disilicate restorations undergo a four-stage
firing or crystallization cycle. This cycle
involves: evaporating and drying of Object
Fix; heat transfer to the restoration; burn
out of glaze paste organics; sintering and
melting of glaze and shade materials; and,
ultimately, crystallization of the lithium
disilicate material. The stages in this
process are drying and closing, heating,
holding and cooling, all of which usually
takeacombined19minutes and50seconds
inorder to ensure a flexural strengthof 360
MPa (± 60); a linear thermal expansion of
10.5 ± 0.5; standard A-D optical properties;
and chemical solubility of <100.2
While it might seem ideal to simply
shorten all of these stages for faster mate-
rial crystallization, each stage does serve a
specific function significant to completing
full crystallization. Therefore, arbitrarily
shortening any or all of these stages can
lead to negative ramifications to the
restoration, including poor glaze, shade
mismatch, reduced strength, cracking
or residual lithium silicate,
which is highly soluble.3
Recently, the four stages
of the crystallization process
Saving Time With the
Speed Crystallization Technique
Creating an In-office Posterior LithiumDisilicate Restoration
C A S E S T U D Y | | | b y R i c h R o s e n b l at t, D . M . D .
were examined to determine where
potential processing time could be saved
while still achieving complete crystal-
lization and without negatively affecting
material quality. The drying stage, which
requires 1.5 minutes, could not be short-
ened — this stage is necessary for drying
out the organics in the glaze and object.
A fixed amount of energy is required and
cannot be modified. Likewise, the cooling
stage, which takes 5.5 minutes, depends
upon time to reduce the temperature of
the restoration. Cooling too fast generates
residual stress inceramic, leading tocracks.
However, the heating stage (approxi-
mately 5.5 minutes) and holding stage
(approximately 7 minutes) are areas in
which times could be reduced. The heating
stage can be reduced due to the higher
initial temperature in phase one, while the
holding phase can be reduced due to better
temperature control. By focusing on these
two stages, the overall crystallization time
can be reduced from19:50 to 14:50minutes,
while still achieving complete crystalliza-
tion, strength and optimumesthetics.
The Speed Crystallization Process
As a result of these investigations, a speed
crystallization process has been intro-
duced for CAD-fabricated lithium disili-
cate restorations (IPS e.max CAD). This
can help dentists save time during the
in-office fabrication process while still
producing highly esthetic and durable
restorations. This speed crystallization
process for lithium disilicate (IPS e.max
CAD) now takes 14 minutes and 50
seconds and still produces restorations
with the requisite physical characteristics.
The Speed Crystallization process incor-
porates the use of the Programmat CSOven
P3, as well as a new speed crystallization
tray (IPS e.max CAD Speed Crystallization
Tray). Suitable for use for crystallizing a
maximumof tworestorations, theprocess is
designed for use only with IPS e.max CAD
Crystallization Glaze Spray, and only with
HTandLTblocks (not for ImpulseShades).
The smaller speed-crystallization tray,
which is composedof silvernitride, requires
less energy for heating and cooling, thereby
contributing to an accurate and efficient
process. The Speed Crystallization tech-
nique can only be properly completed using
the smaller tray, since it takes less time to
heat up and cool down. This is part of the
four-minute reduction in the cycle.
Additionally, the new firing program
for the Programmat CS (i.e., P3) produces
a stand-by temperature of 550° C. This
ensures a complete transition from lith-
ium-metasilicate to lithium-disilicate
for long-term clinical success. It also
achieves the correct shade and translu-
cency for optimum esthetics.
The following case study describes the
protocol followed to produce an in-office
The SpeedCrystallization
technique resulted in an
esthetic and accurately
fitting restoration in less
time than is normally
involvedwith chairside
lithiumdisilicate
restorations.