CASTING INVESTMENTS AND CASTING PROCEDURES

CASTING

production of a shape by thrusting a molten liquid or plastic material into a mold

INVESTING

• process of producing the mold

• covering or surrounding something

LOST WAX CASTING TECHNIQUE

Involves creating a mold by coating an expendable wax pattern with a heat-resistant slurry that hardens at room temperature

abutment

what is the tooth that holds the restoration called?

• TYPE IV (DIE STONE)

• TYPE V (IMPROVED GYPSUM DENTAL STONES)

what types of die stone are commonly used for making dies?

The die

where is the wax pattern made from>?

A. CRUCIBLE FORMER SPACE

B. SPRUE

C. “CROWN” SPACE

D. RESERVOIR

E. INVESTMENT MATERIAL

F. CASTING RING LINER

G. CASTING RING

label

WAX PATTERN FABRICATION

wax form that is the positive likeness of the final restoration

1. form a mount for the wax pattern and fix the pattern in pace so the mold can be made

2. hold the wax pattern in position

3. be an avenue where molten metal can go to the mold of the restoration

4. channel for elimination of wax during burnout procedure

what is the purpose of a sprue?

Shrinks

What happens to molten metal when it sets?

Sprue and reservoir

What are the things that contribute to the compensation for the setting shrinkage of the molten alloy?

same size as the thickest bulk of the pattern

what should the diameter of the sprue be?

• “suck-back” porosity

• distortion due to pressure

• porosity bc of difficulty of metal going through

• large sprue + thick wax pattern =

• thick sprue + thin wax pattern =

• thin sprue + thick wax pattern =

point of greatest bulk in the pattern.

where should the sprue former be placed?

sprue will deform

what happens if you place the sprue on a thin portion of the wax pattern?

• it will have a thick clearance

• it will have a big space on the top which makes it hard for gasses to escape

• \the metal would not flow

What happens if the sprue length is too long?

• there is inadequate clearance

• there is a short space from the top which makes it easy for gasses to escape

• there is a possibility for the material to fracture/break

what happens if the sprue length is too short?

GYPSUM BONDED INVESTMENT - 6mm

PHOSPHATE BONDED INVESTMENT - 3-4mm

what is the clearance needed for the typed of investment materials?

CASTIING RING LINER

lines the interal diameter of the ring

CASTING RING

• metal tube in whcih a refractory mold is made for casting dental restorations

• CONTAINER for investment material while it sets

1. COMPLETE RING

2. SPLIT RING - kayang bumuka without a liner to allow for expansion

What are the kinds of casting rings?

CASTING RING LINER

• allows for greater setting expansion in the investment material

• has the ability to absorb water especially if cellulose or paper is used

• happens when gypsum produce is allowed to set while in contact with water

what is hygroscopic setting expansion?

there will be thin and thick areas that will lead to deformities

what happens if the liner overlaps in the ring?

3mm from the top and bottom of the ring and should be at least 1mm thick for it to allow expansion

what is the clearance for the casting ring liner?

1. ASBESTOS

   1. traditionally used; carcinogenic

2. ALUMINOSIICATE CERAMICS

3. CELLULOSE

   1. light paper; usually used now

what are options for materials to use as a liner?

DRY

• uses sticky wax

• may involve semi- hygroscopic setting expansion if placed in water after pouring

WET

• helps cause semi-hygroscopic setting expansion

• uniformly wet

• avoid squeezing

what are the casting ring liner technques?

• REFRACTORY AND THERMALLY STABLE

• NO CHEMICAL INTERACTION WITH METAL SURFACE

• EASY TO REMOVE FROM METAL CASTING

requirements for investment material?

• for casting GOLD alloys

• it cannot be used for other alloys

what are gypsum bonded investments used for?

BINDER

• a-hemihydrate of gypsum

FILLERS: silica polymorphs

• quartz

• tridymite

• cristobalite

• fused quartz

MODIFYIG AGENTS

COLORING MATTER

REDUCING AGENTS

what is the composition of gypsum bonded investments?

for alloys with a higher melting temperature

what are phosphate bonded investments used for

PHOSPHATE BONDED INVESTMENTS

which investment material should you use if your alloy has a higher melting temperature?

SILICA FILLER: 80% BY WEIGHT

BINDER

• magnesium oxide (basic)

• monoammonium phosphate (acidic)

composition of phosphate bonded investments?

FILLERS

• silica and magnesium oxide

BINDER

• silica gel that reverts to silica (cristobalite) on heating

composition of ethyl silicate bonded investments

1. HAND INVESTING

2. VACUUM INVESTING

3. PAINT-OFF TECHNIQUE

Methods of investing?

HAND INVESTING

manual mixing and pouring of investment

VACUUM INVESTING

• mixing of material is completed in a vacuum

• porosity is reduced

• smoother texture and with better detail

• tensile strength increased

• eliminates porosities and bubbles

PAINT-OFF TECHNIQUE

• done after mixing

• wax pattern is painted with wet investment material

GYPSUM BONDED INVESTMENT

• Hygroscopic expansion technique: 500C

• thermal expansion technique: 700C

PHOSPHATE BONDED INVESTMENT

• 700-1300C

ETHYL SILICATE BONDED INVESTMENT

• 1090C

burnout temperature for different types of investments

1. SIZE OF RING

2. BURNOUT TEMP

3. NUMBER OF RIGS

4. TEMP OF OVEN AT THE START OF BURNOUT

factors affecting burnout time

1. WAX EXPANSION

2. SETTING EXPANSION

3. HYGROSCOPIC EXPANSION

4. THERMAL EXPANSION

compensation for shrinkage of metal after cooling

CASTING

Process of filling the space with molten metal

HEAT SOURCE AND CASTING FORCE

basic requirements of casting

1. DISTORTION

2. SURFACE ROUGHNESS, IRREGULARITIES

3. POROSITY

4. INCOMPLETE CASTING

defects in casting