LABORATORY NOTES FOR CAST GOLD RESTORATIONS

by Richard V. Tucker, D.D.S.

1. Pouring Model
   1. Rinse and clean impression with room temperature water.
   2. Spray the impression with surfactant.
   3. Pour the impression immediately.
   4. Use a die material with minimum expansion and maximum hardness. (Fujirock - golden brown).
   5. Weigh the die material and measure the distilled water to manufacturer's specifications. 25gm. powder - 5 cc. water.
   6. Line up the pins so dies can be withdrawn.
   
   
2. Articulating
   1. Cut key way on each side of pin.
   2. Paint around dowel pin with separating medium.
   3. Pour one half of the impression at a time.
   4. Pour the opposing cast and mount on articulator.
   5. Remove impression from the casts
   6. Immediately pour a back-up die.
   7. Allow the die material to set at least five hours.
   
   
3. Preparation of Dies
   1. Separate dies with coping saw and thin blades. Treat dies very carefully.
   2. Trim dies with sharp knifes and - not with a bur.
   3. Do not use cyanoacrylate (Super - glue) on the dies.
   4. Do not wet or wash dies.
   5. Do not soak dies in lubricant.
   
   
4. Waxing
   1. Brush on Yeti Lube sparingly.
   2. Paint opposing and adjacent teeth with die lube.
   3. Apply wax (Yeti Undercoat Wax - Bordeaux) evenly, flowing into all line angles and point angles.
   4. Flow wax over entire surface of the die before allowing it to harden, in order to avoid lines and voids in the patterns.
   5. Build wax to excess with Yeti Modeling Wax - Gray.
   6. Establish contacts.
   7. Melt occlusal wax with a hot spatula and close articulator to register bite.
   8. Carve and finish the wax pattern immediately after the wax is built up.
   9. Avoid scraping the die margins with carving instruments.
   10. Avoid reapplying wax over a once-carved margin.
   11. Be sure wax is cool
   12. Avoid repeated removal of wax pattern.
   
   
5. Spruing
   1. Sprue pattern on the die.
   2. # 12 round wax shape, cut approximately 1/8 inch long, can be use as blind vents, for finger extensions, or long extensions
   3. Place main sprue on heaviest part and attach with Yeti Stick on Wax.
   4. On contact opposite main sprue, place 1/8 inch blind vent. Run an auxiliary sprue from blind vent to sprue base.
   5. Do not distort pattern on removal.
   6. Apply surface tension remover - (Wax It).
   
   
6. Investing
   1. Invest immediately - do not allow it to set on the sprue former.
   2. Line the ring with asbestos or asbestos substitute with two liners.
   3. Allow a few millimeters of the end of the ring to be free of liner.
   4. Use room temperature distilled water with investment.
   5. Measure both water and powder accurately.
   6. Spatulate 10 seconds for thick mixes and 20 seconds for thin mixes.
   7. Use vacuum investor. Novocast Investment (Whip Mix) 50 grams powder, no water bath.
      • Full crown - 15.5 cc. water - 1175 degrees F.
      • 7/8 and æ crowns - 18 cc water - 1150 degrees F.
      • MOD inlays - 18.5 cc. water - 1150 degrees F.
      • MOD onlays - 18 cc. water - 1150 degrees F.
      • DO, MO. Occlusal inlays - 15 cc. water - 1175 degrees F.
   
   
7. Burn Out
   1. Allow investment to set at least one hour.
   2. Carve off end of investment in the ring.
   3. Place in a cool furnace.
   4. Be sure furnace is calibrated.
   5. Run furnace to temperature - heat rate approximately 20 to 25 degrees per minute - about 1 hour.
   6. Heat soak for at least 20 minutes
   7. Use air and gas flame (not oxygen).
   8. Do not over heat the gold. Dust with flux, as soon as the gold rolls together.
   9. Kerr broken-arm casting machine is good.
   10. Use a Type II gold, Brinell hardness 95 - 110, approximately 80 % gold alloy.
   11. Let gold cool in ring before breaking out.
   12. Brush casting clean and place in an ultrasonic cleaner.
   13. Boil in reducing solution (Prevox).
   
   
8. Finishing
   1. Follow Cast Gold Laboratory Finishing Technique
   2. Keep a log of each casting with the laboratory variables noted,- e.g. water/powder ratio, setting time, burnout temperature, and rate, number and type of ring liner, etc.

Special note: While waxing, remove as much bulk from the inside as possible with a sharp discoid or cleoid instrument.

Special note: Do not leave excess wax at the margins or finish the castings on the die.