1. GYPSUM & ITS
PRODUCTS
BY DR.SHIVA SAI VEMULA
1ST YEAR PG
DEPARTMENT OF PROSTHODONTIC

2. CONTENTS:-
• INTRODUCTION
• HISTORY
• TERMINOLOGY
• USES OF GYPSUM PRODUCTS
• CLASSIFICATION
• APPLICATION
• COMPOSITION
• DIFFERENCE BETWEEN PLASTER AND STONE
• THEORIES OF SETTING
• PROPORTIES:-
• STAGES OF SETTING
• SETTING EXPANSION
• FACTORS EFFECTING SETTING,MIXING,WORKING TIM
• FACTORS EFFECTING THE STRENGTH
• WATER /POWDER RATIO
• RECENT DEVELOPMENTS
• REFERENCES

3. GYPSUM :- it is natural form Calcium sulfate dihydrate of mined
around the various parts of world in a massive form
know as ROCK-GYPSUM
The word gypsum derived form the greek word
“gypsos” meaning chalk
Water returns gypsum to original rock form so its
called as “wonder mineral”
Philips pfaff in 1756 introduced into dentistry
It is second softest mineral on the
Moh’s hardness scale
INTRODUCTION:-

4. Gypsum – Natural Forms
ALBASTER SATIN SPAR SELENITE
 Pure white
 Translucent
white
fibrous needle like
silky luster
Colourless
Crystalline
Transparent

5. HISTORY:-
Oldest traces of plaster
Anatolia and Syria
9000 years old
The king Solomon’s
temple is constructed
with Alabaster gypsum
Egypt’s – CHEOPS
PYRAMID
5000 years old

6. • The name plaster of Paris – Montematre near to Paris where the
large manufacture of Gypsum takes place
• The king of France – after the big London fire destroyed the city in
1966, He covered all walls in his palace with plaster
• Windows made of transparent gypsum – Selenite gypsum

7. TERMINOLOGY:-
• CAST:- It’s a positive, dimensionally accurate replica of the soft and
hard tissues of either maxillary or mandibular jaws and used of
construction of dental appliances
• DIE:- it’s a positive, dimensionally accurate replica of a prepared
natural tooth and used for the construction of inlay , crown or bridges.
• MODEL:- It is a positive, dimensionally accurate replica of oral soft
and hard tissues used as a study model or for patient education .The
progress of treatment can be shown to the patient with these models

8. • MODIFIERS:-They are the chemicals added in order to alter some
of the properties like expansion, setting time etc. or to enhance the
other properties like working time, dimensional stability etc.:-
EX:- accelerators and retarders
• ACCELERATORS:-The substances which decreases the setting
time of gypsum products by increasing the rate of reaction are called
accelerator.
EX:-sodium sulphate, potassium sulphate and sodium chloride
(low concentration)
• RETARDERS:- They are the substances which increases the setting
time of gypsum products by decreasing the rate of reaction
EX:-Borax, sodium chloride, sodium sulphate(high concentration)

9. • SPHERULITES:- As the reaction proceeds gypsum is formed in
the form of needle like clusters called spherulites.
• SOLUBLE PLASTER:-When impression plaster contain potato
starch to make the impression soluble it is termed as ‘soluble plaster
Impression Starch swells
Poured with in hot water and impression Cast
get separated
the cast(after disintegrates
Hardening)
• EXCESS WATER:- The actual amount of water necessary to mix
the calcium sulphate hemihydrate is greater than the amount
required for the chemical reaction, this is called excess water

10. • BALANCED STONE:- A stone with a setting time established by
the addition of proper quantities of both accelerator and retarder is
called “balanced stone”.
• WATER/POWDER RATIO:- It is defined as amount of water
required for 100gm of powder.(18.6gm)
• INDUCTION PERIOD:- Initial time during setting before release
of exothermic heat.
• HYGROSCOPIC EXPANSION:- It is increased expansion of
setting plaster in presence of water .It can be double the amount of
normal setting expansion.
USES:- It is used to expand some gypsum bonded investments.

11. 1 min
7 min
11 min
Working
time
Setting
time
Mixing
time
Mixing
interval
Working
interval
Setting
interval
Initial Setting time
= working time
(loss of gloss)
Final Setting time
=setting time – initial
set
0min Gypsum setting stages

12. • MIXING TIME:- It is the time from the addition of the powder to
the water until mixing is complete.(1 min)
• WORKING TIME:- Time from start of mix to the point where
the consistency of the mix is no longer acceptable for the usage of
indented purpose
• SETTING TIME:- the time elapsing from the beginning of
mixing until the material hardens.

13. • INITIAL SETTING TIME:- The viscosity of the mass is
increased and it can no longer be poured. The material become
rigid(but not hard).It can be carved but not moulded. This is
known as initial setting time.
• FINAL SETTING TIME:- the material can be separated from
the impression without distortion or fracture
• WATER OF CRYSTALLIZATION:- The invisible water
present in the gypsum is known as water of crystallization.

14. USES OF GYPSUM:-
• Impressions of face and mouth
• For making moulds, study casts, diagnostic cast, preliminary cast,
master cast and dies
• Cast partial dentures:-

15. • Mounting the casts:- • Bite registration :-
• Investment and divestment:- • Flasking :-

16. CLASSIFICATION
• Based on ADA-25
GYPSUM
TYPE – 1
IMPRESSION
PLASTER
TYPE – 2
DENTAL
PLASTER
TYPE – 3
DENTAL
STONE
TYPE – 4
DIE STONE
TYPE – 5
DIE STONE
WITH
STRENGTH

17. GYPSUM
Natural
Ex:-rock form
Synthetic
Ex:- By-products of
phosphoric acid
• Based on availability

18. GYPSUM PRODUCTS
Based on hemihydrate
Beta hemihydrate Alpha hemihydrate
Impression
plaster
Dental
plaster
Dental
stone
Die stone Die stone With
high strength
and expansion
Irregular
Porous
Sponge
Loose
Regular
Prismatic
Smooth
Tight
Dry Wet

19. ALPHA HEMIHYDRATE /STONE
CLASS-1 CLASS-2 CLASS-3
Dental
stone/hydrocal
Die stone with
high strength
Die strength with high
strength and high
setting expansion
30% cacl2/mgcl2 is added and autoclave done
in presence of Sodium succinate-0.5%

20. Hydrocal
Densite
Crystocol
impression

21. COMPOSITION
MAIN RECTIVE
INGREDENT
CaSo4,Alpha/Beta hemihydrate
ACCELERATOR
K2So4, 4%increses rate of setting
RETARDER
Borax 0.04% decrease rate of
reaction.
COLOURING AGENT
0.04% Alizarin.
POTATO STARCH
Soluble plaster and permit rapid
separation of cast.

22. APPLICATION

23. PLASTER/BETA
HEMIHYDRATE
STONE/ALPHA
HEMIHYDRATE
• Needle like clusters • Rod and prism like clusters
• Irregular
• Porous
• Regular
• Non porous
• Loosely packed • Closely packed
• Heated in open kettle
• Dry calcination
(type-1,2)
• Heated in closed and steam
pressure
• Wet calcination(type-3,4,5)
• Less strong • More strong
• Required more
water/powder ratio
• Required less water/powder
ratio
DIFFERENCE BETWEEN ALPHAAND BETA
HEMIHYDRATE:-

25. Theories of setting reaction
Colloidal theory Hydration theory Dissolution precipitation/
Crystalline theory
Henry louisMahaelis

26. COLLOIDAL THEORY:-
Plaster enter into colloidal state through a
sol- gel mechanism.in sol state hemihydrate particles are converted
into dihydrate and mass convert into solidgel.
Hemihydrate Hemihydrate Dihydrate Dihydrate
water water water
sol sol gel

27. HYDRATION THEORY:-
Rehydrated plaster particles join together through
hydrogen bonding to the sulfate groups to form the set material.
Hemihydrate Rehydration Sulphate group Set into
of particles Dihydrate
Hydrogen Bondwater

28. DISSOLUTION-PRECIPITATION/CRYSTALLINE THEORY:-
Stage-1:-Fluid stage
• Hemihydrate dissolve
• Suspension of hemihydrate
stage-2:-Plastic stage
• Saturated solution of hemihydrate
• Formation of dihydrate
Stage-3:-Firable stage
• Super saturation of dihydrate
• Dihydrate crystal precipite
• Dissolution
• Suspension
• Saturation
• Super saturation
• Nuclear formation
Stages of crystallization

29. Stage-4:-carvable stage
Dihydrate hemihydrate
crystallisation dissolve
This process continuous till all
hemihydrate is converted into
dihydrate
Spherulite formation, Intermeshing,
Entangling and Exothermic heat
Growth of nuclei
Crystallization
Spherulite formation

30. CaSO4. 2H2O CaSO4+ 1/2H2O+1.1/2H2O
on heating
CaSO4 .1/2 H2O+ 3 H2O 2 (CaSO4.2H2O)+heat 3900(cal)
Mixing with water
SETTING REACTION

31. Setting time:- The time elapse from beginning of the mix to until the
material harden is known as setting time
Initial set
Semi-hard mass
No more workable
Not completely set
Final set
Time required for reaction
to completed
Material separated from
impression with out
distortion.
Tests:-
• loss of gloss
• penetration tests -
vicat penetrometer test
• indentation tests –
gillmore test(small needle)
Tests:-
• penetration tests -
vicat penetrometer test
• indentation tests –
gillmore test(large needle)

32. Excess water
is taken to
form
dihydrate
So mix loss
its gloss
9min
Small needle-initial set
¼ lb(113.4gm),1/12
inch
3 min
Large needle-final set
1lb(453.6gm),1/24inch
12+/-4 min
300gm
1mm diameter
5cm long
Beginning of
time to needle
no more
penetrate
• Gillmore apparatus• Loss of gloss • Vicat penetrometer

33. Setting expansion:- the process of outward growth of crystal by the
outward thrust of growing crystal is called nuclei of crystallization
Normal Hygroscopic
Expansion takes place
normal.
0.15%
Expansion takes place
under water.
0.30%(double)
Amount of water is
reduced by hydration
The water of hydration is
replaced by water
Particles are drawn closely Particles are remain in
same distance
Crystals become intermesh
and entangled
Intermeshing and
entangled process is
delayed
Crystal growth is inhibited
due to lack of excess water
So limited expansion
Due to presence of water
longer crystal growth, so
greater expansion

34. Types ADA ISO
Type-1 0.15 0.15
Type-2 0.30 0.30
Type-3 0.20 0.20
Type-4 0.10 0.15
Type-5 0.10-0.30 0.16-0.30
Setting expansion:-
• crystal push each other
(0.06%-0.5%) in the setting
process it expands linearly

35. Factors effecting
setting time(ST)
ST α W:P ratio
ST α temperature
ST α 1/mixing
time
modifiers
Factors effecting
setting
expansion(SE)
SE α mixing time
SE α 1/modifiers
SE α 1/W:P ratio
Factors effecting
hygroscopic setting
expansion(HSE)
HSE α 1/W:P ratio
HSE α mixing time
HSE α modifiers
Time of immersion
in water

36. Strength α1/ W:P ratio
Strength α mixing time
Strength α modifiers
Factors effecting strength:-

37. • Green strength /wet strength:-
presence of excess water
• Dry strength:-absence of excess
water.
• Dry strength is 2 times more than
wet strength.

38. • W:P ratio α setting time
• W:P ratio α mixing time
• W:P ratio α 1/setting
expansion
• W:P ratio α 1/hygroscopic
expansion
Factors effecting water-powder ratio:-

39.  Ideal W:P ratio:-100gm of
plaster required 18.6 of water
 W:P ratio:-0.18mg
Type -1:- 0.50-0.75
Type -2:- 0.45-0.50
Type -3:- 0.28-0.30
Type -4:- 0.22-0.24
Type -5:- 0.18-0.22
Recommended range of water –powder ratio:-

40. Recent advancements:-
• Impregnation of gypsum with a polymer like polystyrene, polyester
and epoxy resins they occupy the porosities and increases
strength and toughness
• Incorporation of wetting agents(lignosulphonates) reduces
water requirement of stone gives stronger and denser stone
• Type of modification done so that the stone which changes to colour
when its ready to use
• Plastics and resins are added to decrease brittleness and improve the
resistance of scratching during carving of wax pattern in newer
products

41. • Quick stone( Type – 3):-
it gives fast setting time and very smooth mix it
is ideally used for lab.
• Dental plaster is added with silica particle so that it can be used as
investment material(750 degrees temperature).
• Divestment:-
die stone + gypsum bonded investments
• Orthodontic stone:-
it has long working time and gives white stone ,this
model glows (wiping with soap)

42. Conclusion
A wide choice of Gypsum Products is available so we should choose
the one or a combination which is most suitable for our desired
requirements.
If we self manipulate gypsum to improve one feature, others may be
sacrificed. So we must follow the manufacturer instructions for better
results and avoid ad-hoc approaches at dealing with Gypsum products.

43. 1.Anusavice K.J.-“Phillips’ Science of Dental materials”
11th edition , 2002.
2. Anusavice K.J.-“Phillips’ Science of Dental materials”
12th edition, 2003
3. Craig’s R.G., Powers J.M. – “Restorative Dental
Materials” 13th edition
4. Clinical aspects of the dental materials marcia gladwin
5.Dental materials science – Ramakrishna
REFERENCES

44. THANK YOU