Weiss: Investing and Casting Flashcards
_____ ______ at the cavosurface margin is critical to good periodontal health and caries prevention.
Margin Adaptation
What should be done JUST PRIOR to investment?
Re-wax the margin area because wax is not dimensionally stable
The wax pattern should be ______ mm occlusal to the margin
1 to 2 mm
If internal defects (voids or folds) are noted, what must be done?
Re-wax
If there are no internal defects and the margins are adapted, what should be done?
Reseat the pattern on the die and refine with nylon
After margin adaptation and refinement, what must be done immediately in order to avoid distortion?
Sprue and Invest
What are some important things to consider in the placement of the sprue?
- Determine thickest portion of the pattern by holding it up to the light
- Do not attach to a critical area of the pattern (contact)
- Do not attach to functional cusps
At what angle to the long axis of the preparation should the sprue be placed?
45 degrees
How do you attach the sprue to the wax pattern?
sticky wax
The sprue has been placed. To prepare the casting ring, a 90 mm strip of ___ ______ should be positioned a uniform ____mm from one end of the ring.
ring liner
2mm
Why must the ring liner be placed a uniform 2 mm from one end of the casting ring?
To allow a little space for expansion
Sprue length should not exceed ____mm.
6
The wax pattern should be ____mm from the top of the casting ring.
6
At what temperature should the water bath be set?
100 degrees F
A 100 degree F water bath is used for which expansion technique?
Hygroscopic
The wax pattern should be placed in the _____ _____ of the casting ring.
Heat Center
Between the casting ring and the pattern there should be ______mm and between the heat center and the pattern should be _____mm.
6
6
To what is the wax pattern attached?
Sprue Base
Which occurs first, attachment to casting ring or attachment to sprue base?
The wax pattern is attached to the sprue base (sprue to dome). Then the casting ring is placed onto the base.
What is used to decrease surface tension?
De-bubblizer (soap)
Prior to investment, what must be wet?
All surfaces of the wax pattern AND the ring liner
True or False: the vacuum mix is used during the investment technique.
True.
Vacuum mix for 20 seconds
2 minute work time…fill the casting ring
Immediately upon filling the casting ring (with gypsum), where must it be placed? For how long?
Place IMMEDIATELY into 100 degree water bath
at least 30 mins. No longer than 3 hours.
What are the two steps in the expansion?
Step 1: Setting expansion. Powder (gypsum) provides expansion by pushing apart the crystals. More POWDER = more expansion
Step 2: Hygroscopic expansion. Water feeds crystal growth. More TIME= more expansion
During wax pattern elimination, what must be removed before placement in the burnout oven?
The sprue base must be removed from the casting ring
Wax pattern elimination occurs in ___ steps and the temperature(s) of the oven(s) is(are):
two
Step 1: oven temp = 200 degrees F
Step 2: oven temp = 900 degrees F
During wax pattern elimination, the mold should be placed in the oven with the sprue end ______.
Down
How long must the mold remain in the Stage 1 furnace?
45 mins
at 200 degrees
What is the temperature of the Stage II furnace?
900 degrees F
What is done with the sprue after removal from the Stage I furnace?
Immediately it must be placed in the Stage II furnace with the sprue end down
How long must the mold remain in the stage II furnace?
1 hour
at 900 degrees
During the gold casting procedure, you will wind the arm of the casting machine ____ complete turns in a _____ direction. Then the arm is secured in position by engaging the _______ _____.
3
Clockwise
Casting arm
What are the four materials needed for the gold casting procedure?
- Crucible
- Gold Alloy
- Cradle
- Metal Tongs
Which gold-casting item is placed on the platform of the casting machine? Which item is placed on the support pins?
Crucible
Cradle
When adjusting the torch, the flame should reach ______ inches.
10 to 12
What are the three areas within the torch flame? Which area is the correct portion for touching the gold?
Torch Flame = oxidizing area, reducing cone, oxidizing area
The reducing should be touching the gold
The reducing cone of the torch flame should be held at what angle to the gold alloy?
45 degrees
How long should the gold be heated within the reducing cone of the torch flame?
Until the gold coalesces into a sphere and the surface becomes shiny (appears to be spinning)
True of False: When using the torch, the flame should be kept moving constantly.
True
Before placing gold alloy into the crucible, the crucible should be _____.
Preheated
How much gold-casting alloy is placed into the crucible?
8 pennyweight
The casting arm is released by placing pressure in a ____direction.
Clockwise
When should the casting ring be placed into cool water?
When the mold loses its glowing red color
Placement of the casting ring into cool water causes the ____ to break away.
Investment
When using previously cast gold, what should be the ratio of old to new?
50:50
What is the last stage of the investing/casting procedure?
Removal of the sprue
