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.
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.Continue Reading