Dental Dentures: Partial | Cosmetic Dentistry
Before investing, paint a thin layer of Wiropaint fine investment on the model with a brush. The fine investment should not be allowed to dry. Depending on the room temperature, investment should take place within 3-5 minutes (Fig. 156).
When fine investment is not used, the surface tension of the wax pattern can be reduced by spraying on a thin coat of Aurofilm and then blowing it dry (Fig. 157).
Coat the inside of the casting ring with vaseline before pressing it firmly over the baseplate of the duplicate model. Since this baseplate, or second base, has been preformed to fit the casting ring, no wax is required to fix the ring to the model (Fig. 158).
Again, using vacuum mixer, spatulate the investment material for 60 seconds under vacuum
Do not use liquid for this phase of investment. Water that has been allowed to stand at room temperature is sufficient. Here, one measuring cup filled to the brim (60 ml) is mixed with 400 g of investment material.
The spatulation of investment material under vacuum not only offers protection against cracking of the mold during burnout, but also reduces the danger of investment particles breaking off as the molten metal is cast into the mold. When the wax pattern is not painted with fine investment, the use of vacuum spatulation can help avoid an increase in the number of bubbles formed on the pattern.
Using the medium intensity setting, vibrate Wirovest into the casting ring (Fig. 159). Vibrating too hard or for too long a period can increase bubble formation. After 10 minutes remove the mold from the ring and allow it to set. After an additional 20 minutes place the mold on its side in the preheating oven. If this minimum setting time is not observed the mold may crack upon heating.
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