cast and die dental material

1. Cast = Model
Die = Metal cast or cast for single tooth
CAST AND DIE
MATERIALS

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

3. 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

4. Types of model and die
Materials
Non-Metallic
1.1. Gypsum productsGypsum products
model and diesmodel and dies
2.2. Investment modelInvestment model
and diesand dies
3.3. Resin diesResin dies
4.4. Flexible diesFlexible dies
5. Cement dies
6. Ceramic dies
Metallic
1. Electroplated diesElectroplated dies
2. Low-fusing metal dies
3. Amalgam dies

5. Non-metallic Cast & Die Materials
I. Gypsum Products

6. Gypsum (CaSo4.2H2O)
Calcination
Heating the (CaSo4.2H2Oo) at
115o
C in open kettle
Autoclaving
Heating the (CaSo4.2H2O) at
125o
C with steam under pressure
Boiling
Boiling the (CaSo4.2H2O) in 30%
CaCl2
β - 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

7. 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 0
C in
open kettle
Autoclaving Of
Ca So4
.2H2
O at 125 0
C
Boiling Of
Ca So4
.2H2
O in 30 % Cacl2
Particles β - Ca So4
. ½ H2
O
- Irregular
- Non homogenous
- Porous
α - Ca So4
. ½ H2
O More -
Regular
- More homogenous
- Less Porous
α - Ca So4
. ½ H2
O
- 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
Compressiv
e 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 cast
2. Mounting of Casts on
1.As 2ry cast (Working
Cast) in Complete
1.As working wast for crown
& bridge work

8. 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;

9. 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 growth
4. 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)

10. Ca So4. ½ H2O + 2 H2O → Ca So4. 2 H2O + ↑ Heat
Nuclei of
crystalization
Crystal growth Intermeshing
Steps of gypsum setting process

11. Gypsum products
(Setting reaction. Cont.d.)
Controlling the setting reaction (i.e. Setting time):
Role of the manufacturer
1. Particle size
2. Additives (Accelerators and retarders)
Role of the operator
1. Liquid / Powder ratio
2. Mixing rate
3. Mix temperature

12. Gypsum products
SETTING EXPANSION:
- Mechanism of setting expansion
1. 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 expansion
1. Liquid / powder ratio
2. Mixing rate
3. Additives (Anti-expansion agents)

13. 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).

14. 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

15. Gypsum products
(properties. Cont.d)
5. Practicability
- Easy manipulated
- Inexpensive
- Long shelf life if stored in dry conditions

16. Non-metallic Cast & Die materials
2. Resin die Materials

17. 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

18. 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

19. 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

20. THANK YOU