Cast = Model

Die = Metal cast or cast for single tooth

CAST AND DIE MATERIALS

Relationship of impression to cast Cast is the opposite for impression and vice

versa

Ideal Requirements of Model and Die Materials

1. Sufficient mechanical properties (Impact strength, Hardness and tensile strength)

2. Dimensionally stable

3. Compatible with impression materials

4. Colored

5. Easy manipulated

Types of model and die Materials

Non-Metallic

1.1. Gypsum products Gypsum products model and diesmodel and dies

2.2. Investment model Investment model and diesand dies

3.3. Resin diesResin dies4.4. Flexible diesFlexible dies5. Cement dies6. Ceramic dies

Metallic

1. Electroplated diesElectroplated dies2. Low-fusing metal dies3. Amalgam dies

Non-metallic Cast & Die Materials

I. Gypsum Products

Gypsum (CaSo4.2H2O)

CalcinationHeating the (CaSo4.2H2Oo) at

115oC in open kettle

AutoclavingHeating the (CaSo4.2H2O) at

125oC with steam under pressure

BoilingBoiling the (CaSo4.2H2O) in 30%

CaCl2

- Ca So4. ½ H2O α - Ca So4. ½ H2O α - Ca So4. ½ H2O

Dehydration

Type I gypsum(Impression

plaster)

Type II gypsum

(Model plaster)

Type IV gypsum(Extra hard

stone)

Type III gypsum(Hard stone)

Clinical material

Type V gypsum(Extra hard-

high expansion stone)

Laboratory materials

Difference Model plaster Hard stone Extra hard stone

Source Ca So4.2H2 O Ca So4.2H2 O Ca So4.2H2 O

Manufact-uring

Heating Of Ca So4.2H2 O at 115 0C in

open kettle

Autoclaving Of Ca So4.2H2 O at 125 0C

Boiling Of Ca So4.2H2 O in 30 % Cacl2

Particles - Ca So4. ½ H2O

- Irregular - Non homogenous- Porous

- Ca So4. ½ H2O More -

Regular- More homogenous- Less Porous

- Ca So4. ½ H2O

- The most regular- The most homogenous- The least porous

P/L ratio 100 gm / 50-60 ml 100 gm /35-40 ml 100 gm / 25-30 ml

Excess water The largest amount Less amount The least amount

Compressive strength

The weakest More strong The strongest

Tensile strength

The weakest More strong The strongest

Surface hardness

The Least hard More hard The hardest

Setting expansion

0.30% (The highest) 0.20% 0.10% (The lowest)

Setting time 15 Min 15-45 Min 15 Min

Uses 1. As 1ry cast2. Mounting of Casts on the articulator3. In flasking

1.As 2ry cast (Working Cast) in Complete Denture work2.In flasking

1.As working wast for crown & bridge work

Gypsum products

SETTING REACTION:

- After mixing of Ca So4.1/2 H2O powder with water

- A Chemical reaction named crystallization will start during which Ca So4.1/2 H2O changes into intermeshed Ca So4.2 H2O through a series of steps as follows;

Gypsum products(Setting reaction. Cont.d.)

1. Solubility of hemihydrate in water to form a saturated solution of dihydrate

2. Precipitation of minute dihydrate crystals (Nuclei of crystallization)

3. Crystal growth4. Intermeshing of the growing crystals to form the set

hard mass

This reaction is associated with; - Heat generation (exothermic reaction) and - Dimensional changes (setting expansion)

Ca So4. ½ H2O + 2 H2O Ca So4. 2 H2O + Heat

Nuclei of crystalization

Crystal growth Intermeshing

Steps of gypsum setting process

Gypsum products(Setting reaction. Cont.d.)

Controlling the setting reaction (i.e. Setting time):

Role of the manufacturer1. Particle size2. Additives (Accelerators and retarders)

Role of the operator 1. Liquid / Powder ratio2. Mixing rate3. Mix temperature

Gypsum products

SETTING EXPANSION: - Mechanism of setting expansion1. Interaction between the growing crystals will result in

formation of stresses 2. Release of these stresses will lead to outward thrusting of

the crystals, increasing the distances in between, that permit further growth until inter-meshing occurs

- Controlling the setting expansion1. Liquid / powder ratio2. Mixing rate3. Additives (Anti-expansion agents)

Gypsum products

PROPERTIES:

1. Biologically- Wear gloves to avoid skin irritation

2. Interfacially- Separating medium is required if the impression is

made of impression plaster- Precautions are required with hydrocolloids (Water

content) and condensation polymerized rubber impressions (By-products).

Gypsum products(properties. Cont.d)

3. Mechanically- Acceptable compressive and tensile strength

(N.B. Stone > Plaster)- Low values of surface hardness

4. Chemically- Degree of setting expansion

(Plaster > Stone > extra hard stone,however High exp stone > extra hard stone)

- Surface of gypsum could erode by using chemical disinfectants

Gypsum products(properties. Cont.d)

5. Practicability

- Easy manipulated- Inexpensive- Long shelf life if stored in dry conditions

Non-metallic Cast & Die materials

2. Resin die Materials

Resin cast & Die Materials

A. PMMA was an early type, but higher rate of its polymerization shrinkage is a limiting factor

B. EPOXY RESIN DIES Tougher and more abrasion resistant than extra-hard

stone, but less accurate and less stable dimensionally Used safely with polysulfide (separating medium is

required), addition silicone and polyether rubber impression materials

Epoxy resin dies

Composition: (Two component system)

1. Resin monomer: Viscous material

2. Hardener: Polyamine (toxic and irritant, should not come in contact with skin)

Reaction: - Chemical named Polymerization during which; the

polyamine causes the resin molecules to link together into very large networks of molecules

Characters of Epoxy resin C&D Material

- Working time: 15 min, the mix becomes thicker and gradually get hard

- Setting time: Several hours (1-12 hours)

- Setting shrinkage: 0.03-0.3% and may continue for 3 days after mixing

- Porosity: are liable to be formed as a result of the viscosity of mixed material. So, both

1. The use of Centrifuging during impression pouring… and 2. Using of Automixing system help in minimizing the porosity

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