A comprehensive lecture by Dr Rashid Hassan covering all the aspects of different types of model and die materials. Easy ti understand ans recall. For video lectures on different topics of Dental Materials visit and follow Dr Rashid Lectures on Dental Materials (dmbydrrashid) on Facebook.

1. By
Dr. RASHID HASSAN

2. MODEL & DIE
MATERIALS
1) Gypsum products
2) Epoxy products

3. MODEL & DIE MATERIALS
Dental Cast
A positive and accurate
reproduction of a
mandibular or maxillary arch
or a portion,
made from an impression of
that arch.
Model
A positive replica of several
teeth and surrounding
structure or an edentulous
arch, which is prepared from
an impression.
Die
A positive replica of a single
tooth, prepared from an
impression.

4. MODEL & DIE MATERIALS
MODEL PLASTER:
Weakest and most
porous form of gypsum
product used in
dentistry.
DENTAL STONE:
A stronger and less
porous form of gypsum
product used in
dentistry.
DIE STONE:
The densest form of
gypsum product used in
dentistry.
4

5. MODEL & DIE MATERIALS
DIAGNOSTIC CASTS:
The casts generally used for
patient education,
treatment planning or
tracking the progress of
treatment. (e.g.
orthodontic models)
WORKING CAST:
The cast that is strong
enough to resist the
stresses of fabricating an
indirect restoration or
prosthesis.
POURING:
The process of introducing
the flowable gypsum
product into the
impression. 5

6. MODEL & DIE MATERIALS
GYPSUM DENTAL INVESTMENT:
A refractory material, consisting of silica and gypsum as
a binder. Used for taking moulds for metal casting
process.
HYGROSCOPIC SETTING EXPANSION:
The amount of setting expansion that occurs when the
gypsum bonded casting investment is immersed in
water.
NORMAL SETTING EXPANSION:
The amount of setting expansion that occurs when a
gypsum bonded casting investment is allowed to set in
air.
6

7. Requirements
Dimensional Accuracy
• Accuracy of fit of
restoration or appliance
depends on the
accuracy of the replica.
• Small dimensional
changes during setting
may be compensated.
Dimensional Stability
• Changes during storage
are more serious
problems.
• Mechanical
properties:
• Strong enough to
avoid accidental
fracture.
• Hard enough to resist
abrasion during
carving wax patterns.

8. Other requirements of dental cast
materials
 Should ideally be fluid at the time it is poured into
the impression.
 Set material should be sufficiently strong to resist
accidental fracture.
 Set material must be hard enough to resist the
abrassion during carving of wax pattern.
 Should be compatible with all the materials it comes
in contact.
 Should have good colour contrast with various
waxes.
8

9. 1) GYPSUM PRODUCTS

10. INTRODUCTION TO GYPSUM
PRODUCTS
• Gypsum is a white
powdered mineral widely
found in nature.
• Used for making dental
casts since 1756.
• Chemical name 
Calcium sulphate
dihydrate.(CaSO.2H2O)
• In dentistry, gypsum is
used in the form of
Calcium sulphate
hemihydrate.
(CaSO.½H2O)
10

11. TYPES OF
GYPSUM PRODUCTS
Current I.S.O standard for dental gypsum
products identifies 5 types .
Type 1: Dental plaster, Impression.
Type 2: Dental plaster, model.
Type 3: Dental stone, die and model.
Type 4: Dental stone, die, high strength,
low expansion.
Type 5: Dental stone, die, high strength,
high expansion.
11
All 5 types are chemically identical but differ in
their physical form depending upon the method used for manufacturing.

12. Gypsum products
12
Plaster of Paris Dental stone
Die stone

13. GYPSUM PRODUCTS
TYPE 1 (DENTAL PLASTER,
IMPRESSION)
• Earliest of impression
materials in dentistry.
• Rigid (non elastic) impression
material.
• Fractures on removal from
undercut areas.
USES:
• For complete denture
impressions.
• Impressions for Maxillofacial
prosthesis.
• Bite registration material.
TYPE 2 (DENTAL PLASTER,
MODEL)
• Also called as model
plaster/laboratory plaster.
• Contains beta hemihydrate &
modifiers.
USES:
• For making study cast &
models.
• For making molds for curing
dentures.
• For mounting casts on
articulator.

14. GYPSUM PRODUCTS
TYPE 3 (DENTAL STONE, MODEL)
• Also called as class I
stone/Hydrocal.
• Alpha hemihydrate with
potassium sulphate
(accelerator) & borax
(retarder)
USES:
• For preparing master cast.
• For making molds.
TYPE 4 (ENTAL STONE, DIE , HIGH
STRENGTH, LOE EXPANSION)
• Also called as class II
stone,/die
stone/Densite/Improved
stone)
• Cast should be separated 1
hour after pouring.
• Type 4 gains max hardness
after 20 hours.
USES:
• For dies used for inlays wax
pattern.
• For crown & bridge wax
pattern.

15. GYPSUM PRODUCTS
TYPE 5 (DENTAL STONE, DIE, HIGH
STRENGTH, HIGH EXPANSION)
• Most recent gypsum
product.
• Has highest compressive
strength.
• Setting expansion increased
to maximum 0.10% to
0.30%.
USES:
• To prepare dies with
increased expansion.

16. Composition
• Gypsum products used in dentistry are formed by
driving off part of the water of crystallization
from gypsum to form calcium sulphate
hemihydrate.
Gypsum Gypsum product + water
2CaSO4.2H2O (CaSO4)2.H2O + 3H2O
Calcium sulphate dihydrate Calcium sulphate hemihydrate
• Application of gypsum product in dentistry
involves the reverse of the above reaction.
(CaSO4)2.H2O + 3H2O 2CaSO4.2H2O

17. Production of Calcium Sulphate
Hemihydrate
CaSO4 + 2H2O CaSO4 + ½H2O
CaSO4 + ½H2O CaSO4
CaSO4 CaSO4
Gypsum Calcium sulphate
hemihydrate
Calcium sulphate Hexagonal
hemihydrate anhydrate
Hexagonal anhydrate Orthorhombic
anhydrate
17
110 - 130ºC
130 - 200ºC
200 - 1000ºC
110 - 130ºC
130 - 200ºC
200 - 1000ºC

18. Method of manufacturing
Model & die materials
DENTAL PLASTER: (Plaster
of Paris/ Soft plaster)
1) Produced by dry
calcination.
2) Grounded gypsum is
heated in an open
vessel/kettle at 110-130
°C.
3) β hemihydrate crystals
are formed.
DENTAL STONE:
1) Calcination is done
under steam pressure in
an autoclave at 120-
130°C at 17lbs/sq.inch
for 5-7 hours.
2) α hemihydrate crystals
are formed.
HIGH STRENGTH (α
MODIFIED) STONE:
1) Wet Calcination is done
by boiling gypsum in
30% calcium chloride
solution.

19. Manipulation
Water to powder ratios
Gypsum Product Water (ml) Powder (g) W/P ratio
(ml/g)
Plaster 50 - 60 100 0.55
Stone 20 – 35 100 0.30
Theoretical
ratio
18.6 100 0.186
 Theoretical ratio (0.186) is enough to satisfy
chemical reaction.
 Excess water is absorbed by porosities.

20. Manipulation
HAND MIXING:
• Instruments required are
rubber bowl & stiff spatula
• Water & plaster are taken
according to recommended
ratio.
• Water is taken first in bowl.
• Mixing is done vigorously
with the help of stiff
spatula.
• Continue spatulation till a
smooth creamy mixture is
formed.
• Vibrate the mix to avoid air
entrapment.

21. Manipulation
MECHANICAL MIXING:
 Requires expansive
equipment.
 Mixing is done under
vacuum.
 Gives stronger & denser
cast.

22. SETTING REACTION
• Setting starts
rapidly after mixing
P/W.
• Water becomes
saturated with
hemihydrate.
• Dissolved
hemihydrate is
then converted into
dihydrate.
• Crystals of dihydrate
grow form specific sites
called nuclei of crystals
(crystals are ultimate
units of the substance
from which it was
formed)
• These may be small
particles of impurities,
unconverted gypsum
crystals (calcium
sulphate dihydrate)
within the hemidyrate.

23. SETTING REACTION
• If more water is
added, centers of
nucleation are
more widely
dispersed by the
dilution effect.
• With greater
spaces between
crystals leading to
a significant
reduction in
strength
• Two stages can be
identified during
setting.
• Initial set: During this
stage the material
becomes rigid but not
hard and can be
carved but not
moulded (8-16
minutes).
• Final set: The material
becomes hard and
strong, however
hydration reaction is
not necessarily
completed.(30- 40
minutes).

24. Exothermic Reaction
• The hydration of the
hemihydrate is
exothermic, so heat is
given out during
setting.
• Temperature is
maximum during the
stage of final setting.
• Temperature rise is
negligible at the time
of initial set.
• The magnitude of the
temperature rise
depends on the bulk
of the material used.

25. Measurement of Setting of
Gypsum
TESTS FOR MEASURING
SETTING
• Loss of gloss test for
initial set.
• Gillmore test for initial
setting.
• Gillmore test for final
setting.

26. Measurement of Setting of
Gypsum
GILLMORE
APPARATUS
VICAT
PENETOMETER

27. READY-FOR-USE CRITERION:
 Ready-for-use criterion is a measure of time at
which the set material can be handled safely.
 Ready-for-use criterion is not judged by any specific
test.
 Comes with experience.
 Technically set material is considered ready for use
when the compressive strength is 80%. (attained in
1hr)
 Modern products reach ready-for-use stage in 30
min.
27

28. PROPERTIES OF
GYPSUM PRODUCTS
1) SETTING EXPANSION
2) STRENGTH.
3) HARDNESS & ABRASSION
RESISTANCE.
4) REPRODUCTION OF
DETAILS.
1) SETTING EXPANSION
I. Normal setting expansion.
II. Hygroscopic setting
expansion.
Show linear expansion during
setting (0.05-0.5%)
May be desirable (investment
materials) or undesirable
(impression plaster, dental
plaster, stone)
NORMAL SETTING EXPANSION

29. PROPERTIES OF
GYPSUM PRODUCTS
Control of normal setting
expansion
1) Mechanical mixing.
2) Increase in W/P ratio.
3) Use of modifiers.
4) 4% solution of Potassium
sulphate.
5) Sodium chloride.
6) Borax.
HYGROSCOPIC SETTING
EXPANSION
• Occurs when placed under
water before initial set stage.
• Expansion is greater than
normal setting expansion.
• Used to expand gypsum
bonded investments.
• Reduced W/P ratio increases
the hygroscopic setting
expansion.
• Increased spatulation
increases the hygroscopic
setting expansion

30. PROPERTIES OF
GYPSUM PRODUCTS
2) STRENGTH
• Strength increases rapidly as
material hardens.
• Greater the water = lesser the
strength.
1) Wet strength:
Strength of gypsum when water
is more than necessary for
reaction.
2) Dry strength:
Strength of gypsum when excess
free water is lost due to
evaporation.
FACTORS AFFECTING STRENGTH
1) Temperature.
2) W/P ratio.
3) Spatulation.
4) Addition of
accelerators &
retarders.

31. PROPERTIES OF
GYPSUM PRODUCTS
3) HARDNESS & ABRASION
RESISTANCE
• Good surface hardness &
abrasion resistance is
essential.
• Hardness is related to
compressive strength.
• However surface hardness
& abrasion resistance are
not related.
• Commercial hardening
solutions are available.
4) FLOW
• Depends upon W/P ratio.
• Correctly proportioned mix
has sufficient flow.
• Vibrating the mix improves
flow of gypsum.
• Flow reduces as gypsum
reaches initial set.
• Produce accurate details.
• Important in case of
duplicating casts
5) REPRODUCTION OF DETAILS

32. APPLICATIONS OF GYPSUM PRODUCTS
1. Study models.
2. Working casts.
3. Dies for crown & bridge
work.
4. Models for denture
processing.
5. Mounting cast to the
articulator.
6. Dental impression. (only
type 1 impression
plater)
32

33. 2) EPOXY PRODUCTS

34. EPOXY PRODUCTS
• 2 component systems
I. Resin component.
(viscous material called
as monomer)
II. Hardener. (Polyamine,
causes resin monomer
to polymerize)
• Slow setting reaction. (may
take upto several hours)
• Hardener is toxic & allergic.
PROPERTIES OF EPOXY
PRODUCTS
1) Working time = 15
minutes.
2) Setting time = 1 to 12
hours.
3) Have superior compressive
strength & abrasion
resistance.
4) Not as hard as gypsum
dies.
5) Shrinkage during setting =
0.03% to 0.3%
6) High chances of porosities.

35. EPOXY PRODUCTS
USES
• Used in the fabrication of:
a) Crown.
b) Bridge.
c) Inlays.
All Elastomeric impression
materials.
COMPATIBLE WITH

36. Compatibility comparison of Model & Die
Materials with Impression Materials
MODEL & DIE MATERIAL COMPATIBLE WITH
Gypsum Products
Agar
Alginate
All elastomers
Epoxy resins
Polyether
Addition Silicone (Some require a
separator)
Condensation Silicone (Some require a
separator)
Polysulphide (with separator)

37. Comparison of Properties of Model &
Die Materials
PROPERTIES GYPSUM PRODUCTS EPOXY PRODUCTS
Abrasion resistance Poor Good
Ease of Use Easy Moderately difficult
Time required Minimal Several hours
Equipment required Minimal Minimal
Harmful chemicals None Some
Dimensional change Slight expansion Slight contraction
Accuracy Good Good
Compatibility with
impression materials
Excellent Limited