Dentistry Investment Materials Quiz and Flashcards: Refractory Materials

What is the purpose of the investment material in a 'lost wax' process?

Why is it important for an investment material not to react with wax and alloys?

Which property should an investment material have to compensate for shrinkage during casting?

Why should a dental casting investment be porous?

What is the main reason that an investment material should not decompose at high temperatures?

Which property is essential for an investment material to withstand impact forces of molten alloy?

What is the main purpose of refractory materials in investment materials?

Which of the following is NOT a commonly used binder material in dental investments?

What is the primary function of modifiers in investment materials?

Which type of investment is typically used for casting of removable partial dentures (RPD) with base metal alloys?

What is the primary difference between quartz investments and cristobalite investments?

Which type of investment is suitable for casting metal-ceramic restorations?

Investment Materials

An investment material is a ceramic material used to form a mold for casting metals or alloys using the "lost wax" process.

Ideal Properties of Investment Materials

Should not react with wax and alloys
Should be easily manipulated
Inner surface of the mold should not break down at higher temperatures
Should not decompose at higher temperatures to produce gases that corrode the alloy
Should have enough expansion to compensate for wax pattern and metal shrinkage during casting
Should be porous to allow air or gases to escape during casting
Should produce a smooth surface and fine detail margins on the casting
Should have a long shelf life and be inexpensive
Should have high compressive strength to withstand impact forces of molten alloy

General Composition of Investment Materials

Refractory material (e.g. silicon dioxide, quartz, tridymite, or cristobalite)
Binder material (e.g. α-calcium sulfate hemihydrate, phosphate, or ethyl silicate)
Modifiers (e.g. sodium chloride, boric acid, potassium sulfate, graphite, copper powder, or MgO)

Classification of Investments

Based on type of binder:
- Gypsum bonded investment (e.g. CaSO4 α-hemihydrate)
- Phosphate bonded investment (e.g. monoammonium phosphate)
- Silica bonded investment (e.g. ethyl silicate)
Based on refractory material:
- Quartz investments
- Cristobalite investments
Based on temperature of casting:
- Low temperature investments (e.g. gypsum bonded investment)
- High temperature investments (e.g. phosphate bonded investment)
- Silica bonded investment (e.g. ethyl silicate)

Gypsum Bonded Investments

Uses: forming molds for casting gold alloys for crowns and bridges
Properties:
- Three types of expansion may develop: setting, thermal, and hygroscopic expansion (about 1.3% - 2%)

Learn about investment materials in dentistry, which are ceramic materials used to create molds for casting metal or alloy restorations and appliances. Understand the process of embedding wax patterns in investment material and the burn out process to create mold space.