12 Questions
What is the purpose of the investment material in a 'lost wax' process?
To create a mold space for the restoration or appliance
Why is it important for an investment material not to react with wax and alloys?
To prevent undesirable chemical reactions
Which property should an investment material have to compensate for shrinkage during casting?
Enough expansion
Why should a dental casting investment be porous?
To allow air or gases to escape during casting
What is the main reason that an investment material should not decompose at high temperatures?
To avoid giving off gases that could corrode the alloy surface
Which property is essential for an investment material to withstand impact forces of molten alloy?
High compressive strength
What is the main purpose of refractory materials in investment materials?
To compensate for the casting shrinkage during the heating process
Which of the following is NOT a commonly used binder material in dental investments?
Sodium chloride
What is the primary function of modifiers in investment materials?
To modify some physical and mechanical properties of the investment
Which type of investment is typically used for casting of removable partial dentures (RPD) with base metal alloys?
Ethyl silicate bonded investment
What is the primary difference between quartz investments and cristobalite investments?
The type of refractory material used
Which type of investment is suitable for casting metal-ceramic restorations?
Phosphate bonded investment
Study Notes
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.
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