Investing and casting

Dr. Linninger Mercedes

assistant professor

Semmelweis University, Department of Prosthodontics

Casting investments:

• Lost-wax process

– In use for many thousands of years

– Jewellery, ornaments, decorated objects

– Bronze, gold etc. (ages)

• Investing: wrapping the pattern

• Investment agent: material used for it

Preparation of teeth

Impression taking

Gipsum cast

Wax pattern

Framework

Veneered framework

Cementation of FPD

Precisional dental

casting technique

Wax pattern

Framework

Precisional dental

casting technique

Sprueing the wax pattern

Investing the wax pattern

Burning out the wax pattern

Casting the dental alloy

Deflasking the cast

Sandblasting the framework

Finishing the framework

Lost wax technique

Sprueing the wax pattern

Sprue

Lost-head

(reservoire)

For

preventing

cavities and

porosities, due to the

thermal

contraction

Images from Bego Virtual Academy

Sprueing the wax pattern

Sprueing the wax pattern

Investing the wax pattern

Burning out the wax pattern

Casting the dental alloy

Deflasking the cast

Sandblasting the framework

Finishing the framework

Wax pattern: the preformed applience, we want to cast

Mold: the form we want the molten alloy to cast in

Investing the wax pattern

The casting ring The casting ring with the wax pattern

• Wax shrinkage: 0,3-0,4 %

• Alloy shrinkage: 1,3-1,6 % (noble)

2.0 – 2,3 % (base alloys)

Casting shrinkage

Investing the wax pattern

Investment materials

plaster-

bonded

gypsum

Liquid:

Powder:

Sulfate contained sublimates - toxic

Water ( no controll of the expansion )

Used in case of gold

and acrilyc works

Investing the wax pattern

Investment materials

silica-

bonded

phosphate-

bonded

Heat-resistant particles (quartz, cristobalite)

Bonding agent (plaster- or silica- or phosfate based component)

Liquid

Powder

Total expansion = setting + thermal expansion

(controls the expansion )

Contraction – expansion:

• Liquid contraction: cooling molten metal

• Erectile contraction: during cristallization

• Solid contraction: chilling to room

temperature

Must be compensated by the investment

Expansion of investments

• Setting expansion

– Mixing powder and liquid

• Thermal expansion

– Preheating

Vacuum mixing

Investing the wax pattern

Investing the wax pattern

Investing the wax pattern

Setting

expansion

Sprueing the wax pattern

Investing the wax pattern

Burning out the wax pattern

Casting the dental alloy

Deflasking the cast

Sandblasting the framework

Finishing the framework

Burning out the wax pattern

… in the furnace

Thermal

expansion

Images from Bego Virtual Academy

Sprueing the wax pattern

Investing the wax pattern

Burning out the wax pattern

Casting the dental alloy

Deflasking the cast

Sandblasting the framework

Finishing the framework

The casting technique

Melting the alloy

Casting the alloy

• Open flame

• Induction melting

• Vacuum pressure casting

• Centrifugal casting

Casting the dental alloy

The molten mass

Hot zone

Crucible (melting pot)

Casting mould

Casting the dental alloy

Images from Bego Virtual Academy

Casting the dental alloy

Images from Bego Virtual Academy

Casting the dental alloy

Images from Bego Virtual Academy

Sprueing the wax pattern

Investing the wax pattern

Burning out the wax pattern

Casting the dental alloy

Deflasking the cast

Sandblasting the framework

Finishing the framework

Deflasking the cast

Long cooling time

Sprueing the wax pattern

Investing the wax pattern

Burning out the wax pattern

Casting the dental alloy

Deflasking the cast

Sandblasting the framework

Finishing the framework

Sandblasting the framework

Sprueing the wax pattern

Investing the wax pattern

Burning out the wax pattern

Casting the dental alloy

Deflasking the cast

Sandblasting the framework

Finishing the framework

Finishing the framework

Preparation of teeth

Impression taking

Gipsum cast

Wax pattern

Framework

Veneered framework

Cementation of FPD

Precisional dental

casting technique

Thank You for Your attention!