JOVD 2014 #2: Lost Wax Casting Technique for Metal Crown Fabrication

Question 1

Authors?

Answer 1

Todd McCoy, DVM

Question 2

At a dental laboratory, a replica of hard and soft tissues is created from an impression of a prepared tooth and those adjacent to it. This positive reproduction is termed a _____ when referring to the full arch, and a ______ when referring to the prepared tooth.

˜A) Investment; divestment

˜B) Cast; die

˜C) Base; model

˜D) Die; cast

Answer 2

B) Cast; die

Question 3

Which of the following do not correspond to the lost wax casting technique?

A) ancient technique for making a precise replica of an object by casting it in molten metal.

B) this process involves taking a wax pattern of a dental restoration and converting it into a dental casting alloy or ceramic.

C) uses a wax sprue that act as a channel by which the molten metal travels to create the metal restoration

D) Divesting is the procedure by which wax pattern, sprue, and sprue base are filled within the casting ring with a gypsum based investment material poured slowly to avoid air bubbles

Answer 3

D) Is false; Divesting: procedure by which the investment material is broken away from the casting (after investment has cooled down)

• Lost wax casting:
  
  • ancient technique for making a precise replica of an object by casting it in molten metal.
  • In dentistry, this process involves taking a wax pattern of a dental restoration and converting it into a dental casting alloy or ceramic.
• Dental waxes:
  
  • = a mixture synthetic and natural waxes (minerals, plants, animals), pigments, gums, fats, fatty acids, oils, and various resins
  • Material simple to manipulate, versatile, inexpensive, and do not leave residue
• Pattern waxes = casting waxes used to create a model of dental restoration (crown)
• Wax sprue = act as a channel by which the molten metal travels to create the restoration
• Investing: procedure by which wax pattern, sprue, and sprue base are filled within the casting ring with a gypsum based investment material poured slowly to avoid air bubbles.
• Investment: end product of investing

Question 4

Which type of alloy is most commonly used to fabricate metal crown in veterinary dentistry?

Why?

Answer 4

nickel-based alloys are the most commonly used in vet. dent. because they have good strength, biocompatibility, resistance to wear, and reasonable cost

• Pure metals (ex. Gold) are not strong enough to be used for crowns
• Dental casting alloys
  
  • metals and non- metals mixed
  • favorable properties: density, strength, corrosion resistance in the mouth, and hardness.
  • nickel-based often used because good strength, biocompatibility, resistance to wear, and reasonable cost

Question 5

Liste in the chronologic order the following steps of the lost wax technique:

• Divesting
• Vinyl polysiloxane impression
• Investing
• Mixed stone is poured in impression
• Wax sprue is attached to wax pattern with heat wax
• Molten metal alloy is cast by centrifugal force into the space once occupied by the wax sprue and pattern
• Wax pattern is removed from die and fixed to sprue base
• Cast is cut with a circular disc to separate the prepared tooth (die) from the adjacent teeth
• Restoration is microblasted using ultrafine aluminum oxide particles
• Sprue removal and contouring of metal crown

Answer 5

1. Vinyl polysiloxane impression
2. Mixed stone is poured in impression
3. Cast is cut with a circular disc to separate the prepared tooth (die) from the adjacent teeth
4. Wax sprue is attached to wax pattern with heat wax
5. Wax pattern is removed from die and fixed to sprue base
6. Investing
7. Molten metal alloy is cast by centrifugal force into the space once occupied by the wax sprue and pattern
8. Divesting
9. Restoration is microblasted using ultrafine aluminum oxide particles
10. Sprue removal and contouring of metal crown

Question 6

Name the structures 1, 2 and 3 in the picture?

Answer 6

1. Pattern wax
2. Wax sprue
3. Sprue base