LECTURE 8 (copy) (copy)

 What are the key aspects of casting/pressing in manufacturing technology for dental components?

• Shapes dental components through casting or pressing materials into specific molds

• Common applications: dental crowns, bridges, metal frameworks for dentures

• Advantages: Allows intricate and customized shapes, versatile with various materials

Front: What are the key aspects of cutting off/milling in dental manufacturing?

• Shapes dental materials using cutting or milling machines by removing excess material

• Common applications: crafting dental prosthetics, implant components

• Advantages: High precision, accuracy, adaptable to various materials

What are the key aspects of additive manufacturing in dental technology?

• Builds dental structures layer by layer using additive processes

• Common applications: dental models, surgical guides, prosthetics

• Advantages: Rapid prototyping, customization, suitable for complex designs

 What is investing in dental manufacturing?

• Definition: A manipulation where the prototype of the future structure (e.g., dental prosthesis) is surrounded by a material that retains its shape at operating temperature

• Process of forming a mold is called an investment

What is the lost wax casting process?

• Definition: A method using a wax model to create the mold, with the wax eliminated to form the mold cavity

What are the first six steps of the metal casting procedure?

1. Prepare the Tooth: Prepare the tooth receiving the cast restoration

2. Make an Impression: Create an impression of the prepared tooth

3. Pour Gypsum: Pour gypsum into the impression to make a positive cast

4. Make a Wax Pattern: Create a wax pattern representing the lost tooth structure

5. Sprue the Wax Pattern: Fix the wax pattern in space using a crucible former and sprue former

6. Invest the Wax Pattern: Invest the wax pattern to create a mold

What are the last six steps of the metal casting procedure?

1. 7. Eliminate the Wax Pattern: Burn out the wax in a furnace to form the mold 

2. 8. Force Molten Metal: Force molten metal into the mold 

3. 9. Clean the Cast: Clean the cast 

4. 10. Remove the Sprue: Remove the sprue (connection point) from the casting 

5. 11. Finish and Polish: Finish and polish the casting on the die 

6. 12. Cement the Restoration: Cement the finished cast restoration onto the prepared tooth

shrinkage wax plus allow =?

investment expansion

What are the key properties of investment materials?

• Should not react with wax and metal alloys

• Must be easy to handle

• Must not break down at high temperatures

• Must not release products (gases) that contaminate the alloy surface

• Must have sufficient expansion to compensate for alloy shrinkage

• Must be sufficiently porous to allow air and gases passage

• Should reproduce detail and smoothness of the structure

• Must have a long service life and low cost

• Must have high compressive strength to resist casting forces

What are the key aspects of refractory materials in investment materials?

• Refractory materials can withstand temperatures of at least 1500 degrees in a normal atmosphere

• Commonly used allotropic forms of silica: quartz and cristobalite

• When heated, these materials change crystal structure, decreasing density and increasing volume to compensate for alloy shrinkage

What are the key binding agents in investment materials?

• Bind and set individual refractory particles into a solid structure

• Common binding agents: alpha form of calcium sulfate hemihydrate, phosphates, ethyl silicate

What are the key modifiers in investment materials?

• Added in small quantities to alter properties of investment materials

• Common modifiers: sodium chloride, boric acid, calcium sulfate, graphite, copper or magnesium oxide

What are the three types of investment materials?

1. Gypsum bonded investments

2. Phosphate bonded investments

3. Ethyl silicate bonded investments

 What are the applications and composition of gypsum bonded investments?

used for?

made of?

binder?

can withstand?

composition?

• Commonly used to cast gold alloys for single crowns and small fixed partial dentures, gypsum used in dent = almost pure calcium sulfate dihydrate

• Binder: gypsum

• Used for gold plays, crowns, fixed and removable partial dentures

• Ideal for gold, withstands 700°C temperature

• Composition: gypsum, silica, and modifiers

The components of gypsum bonded investments included are (list five)

name each of their function

by how much do the main three investment materials expand?

1.3 to 2 percent

What are the properties of gypsum bonded investment materials?

expansion types

when do they become brittle!

• Expansion types:

• normal setting expansion -

  occurs as investment hardens in air

• hygroscopic setting expansion -

  occurs while investment is in water

• thermal expansion - occurs as investment is heated

• Sulfur dioxide and sulfur trioxide release above 700°C can make cast alloy brittle

• therefore Not used for high melting point alloys like Cobalt-Chrome and Palladium

What is the setting reaction and setting time for gypsum investment materials?

• Setting reaction involves dissolution and precipitation process

• Hemihydrate particles dissolve and recrystallize into dihydrate form

• Setting time: 5 to 25 minutes from mixing start to complete set

 What factors influence the setting time of gypsum investment materials?

• Solubility of Alpha Hemihydrate: Accelerated by sodium sulfate, retarded by borax

• Crystallisation Nuclei: Accelerates solidification, retards solidification

• Degree of Crystal Growth: Increased by accelerators, decreased by retarders

• Composition Variations: Increasing silica extends setting time

• Powder Size: Finer alpha hemihydrate accelerates curing

• Impurities: Gypsum (dihydrate) shortens curing time

• Water/Powder Ratio: Increased water slows curing

• Mixing Speed: Faster mixing quickens curing

• Mixing Liquid Temperature: Warmer water accelerates curing; beyond 50°C, slows curing

What is the purpose of modifying agents in gypsum-bonded investments

• Control setting rate (accelerators/retarders)

• Protect embedded gold alloy components (reducing agents like powdered graphite or copper)

• Increase thermal expansion (additives like boric acid, soluble halide salts)

What are the disadvantages of gypsum-bonded investments?

• Unsuitable for casting high-melting gold alloys, palladium alloys, and base-metal alloys like nickel-chromium and cobalt-chromium

• Tend to decompose at high temperatures

normal expansion

talk about it in gypsum investments too

Q: What is hygroscopic expansion in investment materials and what factors affect it? (continued)

• Finer particle size of silica increases expansion.

• Higher water/powder ratio results in less expansion.

• Reduced mixing time lowers hygroscopicity.

• Older material exhibits lower hygroscopic expansion.

What occurs during the thermal expansion of gypsum investment material?

• The material expands when heated during casting.

• The amount of expansion depends on the type and amount of silica present.

What causes shrinkage in gypsum investment material and under what conditions does it occur?

l

• Shrinkage occurs when the material cools down below 700°C.

• Shrinkage is caused by the gypsum.

• It is unrelated to the amount and properties of silica in the material.

make on these

What are the two types of strength in gypsum bonded investment materials?

1. Wet or green strength: Strength when excess water is present after initial setting

2. Dry strength: Strength after drying, typically twice as strong as wet strength

1. What are the characteristics of Martensite Steel?

1. Undergoes heat treatment for increased hardness

2. Corrosion resistance varies; heat treatment can affect it

3. Significant increase in hardness through heat treatment

4. Used for surgical and cutting instruments in dentistry

5. Significant impact on hardness through heat treatment

• What are the characteristics of Austenite Steel?

• Addition of Ni stabilizes the austenitic structure

• Provides high corrosion resistance, good ductility

• Increased strength after cold working

• Fine grain structure, easy cold working

• Highest corrosion resistance among the three main steel types

• Applications include dental instruments and components that require corrosion resistance and strength

• Austenitic structure stabilized by Ni

• What are the compressive strength requirements for phosphate bonded investments?

• Type I (for inlays, crowns, etc.): Minimum 2.5 MPa

• Type II (for removable appliances): Minimum 3 MPa

• What are the setting expansion characteristics of phosphate bonded investments?

• Full-strength liquid: About 0.4%

• Hygroscopic technique: Additional 0.6% to 0.8%

• Within 30% of manufacturer's stated value

•  What are the thermal expansion characteristics of phosphate bonded investments?

• 50:50 mixture of liquid and water: About 0.8%

• Undiluted liquid: About 1% to 1.2%

• Within 15% of manufacturer's stated value

• How does temperature affect the mixing and setting time of phosphate bonded investments?

• Hotter mixture sets faster

• Setting reaction generates heat, speeding up curing

• Better mixing and efficiency lead to faster curing and higher temperature

• Mechanical mixing under vacuum preferred for optimal results

advantages and disadvantage of phosphate investments

how is mixing and setting time affected by temperature?

If the mixture is hotter, it will set faster. The setting reaction itself generates heat, which speeds up the curing process. Increasing the mixing time and e%ciency also leads to faster curing and a greater rise in temperature. Generally, the better the mixing, the smoother and more accurate the casting will be.

Mechanical mixing under vacuum is often preferred for optimal results

• What is the binder in ethyl silicate investment materials?

silica

For what applications are ethyl silicate investment materials ideal?

• Base metal alloys partial dentures

• High resistance to heat and wear

• What is the primary use of ethyl silicate investment materials?

• Making molds for the casting of removable partial dentures of cobalt-chromium

• What are the components of the powder composition of ethyl silicate investment materials?

• Refractory silica

• Glass particles

• Minor amounts of MgO (calcined magnesium oxide) and other oxides

advantages and disadvantages of ethyl silicate

setting reaction of ethyl silicate

binding reaction of ethyl silicate

• What is the main ingredient in magnesium-zirconium investment materials?

• Magnesium oxide (acts as both a binder and a refractory)

What additional components are found in magnesium-zirconium investment materials?

• Aluminum oxide

• Zirconium oxide

• Lithium aluminosilicate

• Zirconium silicate

•  What are the three main types of welding?

• Spot welding

• Pressure welding

• Laser welding

• Q: Describe spot welding.

• Clean metal surfaces placed together under pressure

• Current passed through the joint to induce interfacial melting

• Melting starts at the interface and propagates outwards

SPOT ON FACE: interface

• Describe pressure welding.

• Two metal parts placed side by side with a large force applied perpendicular to the surface

• Pure gold, extremely ductile, can be pressure welded by hand

• Force must cause permanent deformations to reveal metal without foil

• Force applied rapidly to compress exposed surfaces before gases are adsorbed

• Surface roughness problems overcome by compressive forces

• Describe laser welding.

• High-intensity coherent light pulse generated by the laser

• Pulse duration and intensity selected to melt metals in a small area

• Beam focused on the joint to melt opposing surfaces

• Expansion from high temperature and change of state forms the weld upon solidification

•  What is soldering and how is it different from welding?

• Soldering joins two metal parts using a metal/alloy with a lower melting point than the parts to be joined

• The solder melts and fills the gap between the parts, solidifies to form a monolithic solid

• What are the requirements for solder in soldering?

• Melting temperature 60-90 degrees lower than the base alloy's solidification temperature

• Similar physical and chemical properties to the base alloy

• Must wet the alloy well

• Must flow over the temperature range of the soldering process

• Must be corrosion resistant and non-staining

• Metals in the solder must not alloy with the base alloy to form undesirable properties

• Q: What are the types of solder based on soldering time and melting temperature?

• Soldering time: Primary (before firing and glazing porcelain) and Secondary (after firing and glazing porcelain)

• Melting temperature: High melting and Low melting

• What are fluxes and their functions in soldering?

• Fluxes: Compounds applied to metal surfaces to dissolve/prevent oxides and other substances that reduce the quality/strength of the soldered area

• Functions:

  • Protective fluxes: Protect surfaces from oxide formation

  • Reducing fluxes: Reduce surface oxide layer to pure metal

  • Dissolving fluxes: Dissolve formed oxides and absorb them

What are the main ingredients and suitable alloys for fluoride fluxes?

• Main Ingredients: Alkali fluorides (KF), Boric Acid (H2BO2), Borax

• Suitable Alloys: Chromium Alloys

what is soldering?

indications for soldering/ when is it used?

• What is the function of anti-flux in soldering?

• Anti-flux is applied to surfaces to prevent solder from flowing onto unwanted areas

• Acts as a barrier to keep the solder in place and ensure it only goes where intended

types of anti fluxes