The mixing bowl is made of flexible material,
either rubber (fig. 8-18) or flexible plastic, and used to
mix alginate impression material and dental stone. It
comes in small, medium, large, and extra large sizes.
All sizes are used in the dental laboratory. A spatula is
used to blend the powdered alginate or dental stone and
water together. You may also find that a regular table
knife may be used as a mixing spatula. In either case,
the rounded ends on the spatula or table knife should
approximate the contour of the mixing bowl.
PNEUMATIC CURING UNIT
The pneumatic curing unit (fig. 8-19) is commonly
called a pressure pot. It is used during the
polymerization of self-curing acrylic resins. It is used
to cure relines and repairs of complete and removable
partial dentures. The unit has a compressed air inlet
that allows air pressure to fill the pot. Curing of the
resin under pressure significantly reduces the
possibility of pores or voids with the resin. Lukewarm
water (115°F) is usually placed in the pot to hasten
polymerization. To use, place the appliance that is to
be cured in the pot. Ensure the appliance is completely
submerged in the water. Secure the pot top. Fill the pot
with compressed air. The normal curing time is 30
minutes at 20 psi.
You must never exceed the maximum air
pressure indicated in the manufacturer's
instructions. Excessive pressure may cause
the pot to explode.
Curing time may vary depending on the thickness
of the resin being cured. After curing, use the air relief
valve to let the air escape. Ensure that no air pressure
remains in the pot when retrieving the cured prosthesis
from the pot.
Figure 8-19.Pneumatic curing unit.
Periodically check the seals, air inlets, and outlets
for malfunction. Activate the pressure relief valve to
ensure it is operational. When necessary, lubricate the
"O" ring inside the lid with petrolatum.
The vacuum adapter (fig. 8-20) is used for the
rapid fabrication of custom trays, stents, mouthguards,
and bite guards. This unit is also referred to as the
vacuum former. The vacuum former will soften a
sheet of plastic or acrylic resin and then draw it onto the
cast with suction.
Figure 8-18.Rubber mixing bowl.
Figure 8-20.Vacuum adapter.