Figure 5 Flasking is done in three steps. In the first step the cast is secured to the base of the flask with stone. No undercuts should exist on the surface of this first stage. In the second stage the upper half of the flask is put in place and stone is poured to the occlusal surfaces of the teeth. The final stage is accomplished when the top portion or capping of the flask is poured and the lid placed on the flask.
The best results are obtained when all three sections are made in stone. Some laboratories pour the first two stages in plaster and the capping in stone to prevent the teeth from being displaced during packing. This method is satisfactory but better results are obtained when all three pours are made of stone.
Figure 6 Stone is mixed and placed in the base of the flask.
Figure 7 The maxillary cast is pushed to place until the bottom of the cast touches the base of the flask. The only exception is when the base of the cast is uneven; then the cast is leveled to permit easy separation and good access in later stages.
Figure 8 Note that the posterior portion of the cast is level with the edge of the flask.
Figure 9 The stone is smoothed even with the base of the cast and is contoured so that no undercuts will be present when the stone is set.
Figure 10 The flask is set aside until the stone reaches its initial set.
Figure 11 When the stone reaches its initial set, a finger moistened with water is used to complete smoothing the lower portion of the flask.
Figure 12 If any small undercut areas exist, they should be trimmed with a knife after the stone has set.
Figure 13 The lower half of the flasking of the maxillary denture is completed.
Figure 14 Similar procedures are followed with the mandibular cast. Note that the posterior portion of the base of the lower flask is higher to accommodate the mandibular cast. The cast has been pushed to the base of the flask and the stone has been brought up around the posterior portion of the cast. No undercuts are present.
Figure 15 A plaster separator is painted on the first stage stone.
Figure 16 The upper half of the flask is put into place and the flask is checked to be sure that the teeth do not protrude above the top of the flask.
Figure 17 The second mix of stone is flowed to place. The flask is resting on a vibrator to be sure that the stone reaches all crevices around the teeth. There will be less likelihood of bubbles forming if the wax denture is first painted with a surface tension-reducing agent.
Figure 18 The stone is vibrated until the teeth are covered.
Figure 19 The stone is wiped off the occlusal surface of the teeth leaving the teeth exposed. The stone is allowed to set.
Figure 20 The second stage of the flasking has been completed for the maxillary and mandibular dentures.
Figure 21 A plaster separating medium is painted on the surface of the second stage stone.
Figure 22 A mix of stone is placed in the top half of the flask. This is referred to as the capping.
Figure 23 The flask is slightly over-filled.
Figure 24 The lid is placed on the flask and is tapped firmly to place. Excess stone will exude through the holes in the lid and around the edges. This stone is not removed until it has set.
Figure 25 The flasking of the maxillary and mandibular dentures is complete.
Now that the dentures have been flasked, the wax must be eliminated to form a mold into which resin may be packed. This is done by placing the flask in hot water, which softens the wax. The flask is then opened and the wax is flushed out. This is not done until the flasking stone has set.
Figure 27 The time required for melting wax in a flask depends upon the size of the flask and the temperature of the water. If the water is at a rolling boil, four minutes is sufficient time to soften wax in an average sized flask. Some boil-out tanks have a tank in which the water is maintained at 135°F. which softens but does not melt the wax. With this type of equipment, the flask may be left in the 135°F. water indefinitely without melting the wax.
Figure 28 After four minutes the flasks are removed from the boiling water.
Figure 29 The blunt end of a plaster knife is used to separate the flask. It is placed in the slot in the posterior portion of the flask and the flask is gently pried apart.
Figure 30 The flasks are opened and the baseplates and softened wax are peeled from the mold.
Figure 31 A dipper with a hole cut in the bottom is used to flush the mold. By having a hole in the bottom of the dipper, clean water is allowed to run over the flask. If some wax is present, it will remain on the top of the water and not contaminate the mold.