1. MODEL AND DIE MATERIAL

2. Definition of model or cast It a positive replica of the teeth and adjacent structures. Definition of die It is a positive replica of the individual prepared tooth on which the inlays and crowns are made.

3. Requirements for model and die materials
1. Should have high strength to resist breakage 
during use.
2. Should be hard to resist scratching during use.
3. It should be able to reproduce fine details of the
impression.
4. It should have little dimensional change on 
setting and should remain dimensionally stable during
storage.

4. 5.Compatibility with impression materials. 
There should be no interaction between the surface of impression and the model and die.
6. Good color contrast with other 
materials being used.
7. Ease of use and cheap.

5. Ideal requirements of die system
1. Easy to remove and replace in its original position.
2. Stable when placed in the cast.
3. Easy to mount in the articulator.

6. Types of model & die materials
Metallic dies
Non-metallic casts
Electroplated Dies
Copper plated
Silver plated
Amalgam used die material
Low fusing metal die
Gypsum
Type I-Impression plaster
Type II-Model plaster
Type III-Hard stone
Type IV-Extra hard stone
Type V –Extra hard, high expansions stone
Resin
Epoxy Resin
Polyurathane
Flexible die materials
Ceramic dies
Cement dies
Types of model & die materials

7. Gypsum products
Most gypsum products are obtained from natural gypsum rock.
Because gypsum is the dihydrate form of calcium sulfate (CaSO4 · 2H2O), on heating, it loses1.5 g mol of its 2 g mol of H2O and is converted to calcium sulfate hemihydrate (CaSO4· ½H2O).
When calcium sulfate hemihydrate is mixed with water, the reverse reaction takes place, and the calcium sulfate hemihydrate is converted back to calcium sulfate dihydrate.

9. Gypsum products are chemically the same (CaSO4
Gypsum products are chemically the same (CaSO4.1/2 H2O) but they differ in:
1. Method of manufacturing.
2. Particle size and shape.
3. Water/powder ratio.
4. Physical and mechanical properties.
5. Uses.

10. Extra hard stone IV, V Hard stone III Model Plaster I, II Difference
CaSO4 · 2H2O
Source
Boiling of CaSO4 · 2H2O in 30% CaCl2
Autoclaving of CaSO4 · 2H2O
At 125 ᵒC
Heating of CaSO4 · 2H2O in open air
At 115 ᵒC
Manufacturing
CaSO4 · ½H2O
Most regular
Least porous
Most homogenous
α-CaSO4 · ½H2O
More regular
Less porous
More homogenous
β-CaSO4 · ½H2O
Irregular
Porous
Non homogenous
Particles
100 gm ̸25-30 mL
100 gm ̸35-40 mL
100 gm ̸50-60 mL
P/L ratio
The strongest
More strong
The weakest
Strength
The hardest
More hard
The least hard
Surface hardness
15 min
15-45 min
Setting time
Working cast for crown, bridge & metallic denture base
Secondary cast
In flasking
Primary cast
Mounting of cast
Uses

11. high-strength stone die

13. Setting reaction
When hemihydrate is mixed with water, the reaction is reversed and the dihydrate is formed.
The reaction is exothermic and depends on:
1. Solubility differences
Where hemihydrates are more soluble in water than the formed dihydrates.

14. 2. Nuclei of crystallization
Where the reaction proceeds leading to precipitation of excess dehydrates in the form of nuclei of crystallization.
3. Crystal growth
During which more dihydrates will be precipitated around the nuclei of crystallization leading to crystal growth.
The reaction continues till all the hemihydrates are transformed into dihydrates.

15. Factors affecting setting time
W/P ratio
Increasing water /powder ratio, decreases nuclei of crystallization and retards the setting time.
Spatulation
Rapid and prolonged spatulation accelerates setting and also increases setting expansion by breaking up some of dihydrate which increases the nuclei of crystallization.
Temperature
Increasing water temperature to a certain level will accelerate setting.

16. Impurities
Impurities will accelerate the setting time by providing nuclei of crystallization.
Fineness
The finer the particle size, the faster the mix will set by increasing nuclei of crystallization.
Accelerators and retarders
Accelerators
Such as potassium sulfate or set gypsum where they act as sites for crystallization and increasing the rate of solubility of hemihydrates.
Retarders
Such as blood, saliva, alginate.
Borax as a retarder forms a coat around the hemihydrate particles and this decreases the rate of solubility or around dihydrates (nucleating sites).

17. Manipulation Water is dispensed into a mixing bowl.
The powder of gypsum products is added and mixed with water to obtain a smooth mix.
Spatulation by hand using a spatula with a stiff blade with the bowl on a vibrator or a power- driven mechanical spatulator.

20. Metallic materials: Electroplated dies
Electroplated dies are made by electrodeposition of metal ions into the fitting surface of an impression material.
It produces a die with
a very hard and smooth surface
registration of fine details

21. Copper electroplating

22. Silver-plated die Copper-plated die Difference
Polysulfide imp.
Silicone imp.
Polyether imp.
Compound imp.
Cathode
Silver bar
Copper bar
Anode
Silver cyanide
Potassium cyanide
Potassium carbonate
water
Copper sulfate
Sulfuric acid
Sulphonic acid
Electrolytic solution
5-10 amp
15-35 amp
Electric current
12-15 hours
10-15 hours
Time required

24. Dental waxes

25. Classification of dental waxes
According to their use and application
1. pattern waxes
Inlay
Casting
Baseplate
2. Processing waxes
Boxing
Utility
Sticky
3.Impression waxes
Corrective
Bite
Bite wax

26. Inlay pattern wax

27. Casting wax

29. Baseplate wax

30. Boxing wax or carding wax

31. Utility wax

32. Sticky wax

33. Write short notes on
Requirements and types of model and die materials.
Differences between types of gypsum products.