D2 Biomaterials Lecture 5: Investing & Casting

What is the term for surrounding the wax pattern with a material that can accurately duplicate the shape and anatomic features of the wax pattern?

Investing

What is the term for removal of the wax pattern so that a mold is created into which molten metal can be forced into?

Burnout

What is the term for introducing the molten alloy into the mold?

Casting

What is the tool used to create a channel that allows the molten wax to escape from the mold?

Spure

What is the tool used to cut materials into crowns?

Milling machine (CNC)

What is required after receiving the final crown product before delivery?

Human adjustment

What is the crown material that stays in the mouth the longest?

Gold

What are the sectioned stone parts on a cast called?

Dies

What is the main aspect of function on wax-up teeth?

Correct occlusion

For what two reasons did zirconia replace porcelain fused to metal (PFM) for crowns?

1. Easy production

2. Predictable

What is the next step after the wax-up is completed?

Use sprue to create escape path for wax

What is the tool used to form the bottom of the investment during use of sprue formers before adding stone?

Rubber base

What is the tool used to contain the stone in the rubber base?

Metal ring

What is the purpose of sprue formers?

Stabilize wax

What is the tool used to eliminate voids in investment materials?

Vacuum mixer

What step of investing material causes the most change dimensionally?

Casting

What should be done after investment material reaches the top of the ring in the rubber base?

Let it set for 1 hour

What is the purpose of putting the investment material in the kiln?

Burnout

What is the system that could be used by dentists for ceramic restorations?

IPS Empress

What must the amount of investment material compensate for?

Alloy's cooling shrinkage

How much shrinkage is caused by the impressions step?

0.1 - 0.2%

How much shrinkage is caused by the finishing/polishing step?

1.5%

How much expansion is caused by the cementing step?

1.5%

How much could gold casting alloys shrink?

1.4 - 1.7%

How much could base metal alloys shrink?

2 - 2.3%

What is the term for an investment that can withstand high temperature using a casting?

Refractory investment

What was the material used for lining casting rings that is not used anymore due to potential health risks?

Asbestos

What are the two materials that are now used as ring liners?

1. Aluminum silicate

2. Cellulose

What should the thickness of liners be?

1 mm

How short of the ring should liners be?

3 mm

What are the three advantages of mixing investment materials?

1. Less porosity

2. Smooth texture

3. More compressive strength

Where should you put the metal ring if you don't immediately burnout?

Humidor

What is the temperature range for phosphate-bonded investments?

700 to 870 C

What is the temperature rate of rise for the burnout furnace?

10 C/min

Why should you burnout while the mold is still wet?

Water reduces absorption of wax

What are the three classifications of dental investments?

1. Gypsum

2. Silica

3. Phosphate

When are gypsum investments used?

Investing of wax for crown and bridge

Why shouldn't you use gypsum investments for casting metal ceramic alloys?

Unstable at higher temperature

What are the two uses of phosphate bonded investments?

1. PFM restorations

2. Gold alloys