just a brief idea about Gypsum product. i study this topic and prepare this ppt.

2. A. INTRODUCTION
B. PRODUCTION OF GYPSUM, PRODUCTS
C. TYPES OF GYPSUM PRODUCTS
D. SETTING OF GYPSUM PRODUCTS
E. SETTING EXPANSION
F. MANIPULATION OF GYPSUM PRODUCTS

3.  GYPSUM (CaSO4.2H2O : CALCIUM SULFATE
DIHYDRATE ) is a mineral mined in various
parts of the world , but it is also produced as
a by product of flue gas desulfurization in
some coal-fired electric power plants .

4. TYPE 1 Dental plaster for impression
TYPE 2 Dental plaster
CLASS 1 For mounting
CLASS 2 For models
TYPE 3 Dental stone for models
TYPE 4 Dental stone ( high strength ,
low expansion)
TYPE 5 Dental stone ( high strength ,
high expansion)

5. TYPE
1
TYPE
II
TYPE
III
TYPE
IV
TYPE
V

6. COMPOSITION:
DENTAL PLASTER +
K2SO4+BORAX+COLORING
&FLAVOURING AGENTS
USES :
a) FOR MAKING IMPRESSION IN
COMPLETE DENTURE PATIENTS
b) MAXILLOFACIAL PROSTHESICS
c) BITE REGISTRATION MATERIAL
IDEAL REQUIREMENTS:
a) SETTING TIME SHOULD BE UNDER
ACCURATE CONTROL
b) FOR BETTER ACCURACY THE
SETTING EXPANSION SHOULD BE
LOW

7. SYNONYM: Dental plaster , model,
mounting, labortory plaster
COMPOSITION
 Contain beta-hemihydrate and
modifiers
IDEAL REQUIREMENTS
 SET RAPIDLY BUT GIVE ADEQUATE
TIME FOR MANIPULATION .
 SET TO VERY HARD & STRONG MASS
 FLOW INTO ALL PARTS
 SHOULD NEITHER CONTRACT NOR
EXPAND WHILE SETTING .
USES:
 FOR MAKING STUDY CAST & MODELS .
 TO MAKE MOLDS FOR CURING
DENTURES.
 FOR MOUNTING CASTS ON
ARTICULATOR.

8. SYNONYMS: CLASS 1 STONE OR HYDROCAL
COMPOSITION:
USES:
FOR PREPARING MASTER CASTS AND TO MAKE MOLDS .
ALPHA-HEMIHYDRATE
COLORING
MATERIAL
2 to 3%
POTASSIUM
SULPHATE(K2SO4)
ACCLERATOR
BORAX RETARDER

9. SYNONYMS: CLASS II STONE
, DIE STONE,IMPROVED
STONE
USES:
 DIE STONE IS THE
STRONGEST AND HARDEST
VARIETY OF GYPSUM
PRODUCT.
 WHEN HIGH STRENGH &
SURFACE HARDNESS IS
REQUIRED.
MODEL BASES, CADD/CAM
DIES & DIES FOR
FABRICATING INLAY,
CROWN & BRIDGE WAX
PATTERN.

10. PROPERTIES :
 HIGH STRENGTH & HIGH
EXPANSION .
 SETTING EXPANSION HAS
BEEN INCREASED FORM A
MAXIMUM OF 0.10 to 0.30%.
EXAMPLES
HARD ROCK , JADE ROCK,
RESINROCK XL5,
DENFLO-HX
USES
TO PREPARE DIES WITH HIGH
EXPANSION.

11. THESE MATERIALS ARE PRODUCED BY CALCINING
CALCIUM SULFATE HEMIHYDRATE.
 COMMERCIALLY , THE GYPSUM IS GROUND & SUBJECTED TO
TEMERATURES OF 110C TO 130C(230F TO 266F) IN OPEN
CONTAINERS TO DRIVE OFF PART OF THE WATER OF
CRYSTALIZATION)

12. DEPENDING ON THE METHOD
OF CALCINATION , THESE ARE
TWO FORMS OF
HEMIHYDRATES.
BETA
HEMIHYDRATES(PLASTER)
ALPHA HEMIHYDRATES
(STONE)
ALPHA MODIFIED
HEMIHYDRATES (DIE STONE )

14. GYPSUM IS CALCINED UNDER
STEAM PRESSURE IN AN AUTOCLAVE AT
120-130C AT 17Ibs/sq.INCH FOR 5-7 hrs.
THUS TE PRODUCT OBTAINED IS MUCH
STRONGER & HARDER THAN BETA
HEMIHYDRATE.

15. PROPORTIONING:
TO SECURE MAXIMUM STRENTH A LOW W/P
RATIO SHOULD BE USED. THE WATER SHOULD BE MEASURED
AND THE POWDER WEIGHED.
WATER/POWDER RATIO:
W/P RATIO IS A VERY IMPORTANT FACTOR IN
DECIDING THE PHYSICAL & CHEMICAL PROPERTIES OF THE
FINAL PRODUCT.

17. IMPRESSION COMPOUND 0.50 to 0.75
DENTAL PLASTER 0.45 to 0.50
DENTAL STONE 0.28 to 0.30
DIE STONE TYPE 4 0.22 to 0.24
DIE STONE TYPE 5 0.18 to 0.22

18. SETTING
TIME
MODIFIERS,
MANUFACTURA
ING PROCESS
W/P
RATIO
TEMPERATUR
E, MIXING &
SPATULATIO
N

19. ACCELERATOR :
IF THE CHEMICALS ADDED
DECREASES THE SETTING TIME , IT IS
CALLED AN ACCELERATOR.
RETARDER:
IF IT INCREASES THE SETTING
TIME , IT IS CALLED RETARDERS.
ACCELERATOR SODIUM OR POTASSIUM SULPHATE
(2 to 3%)
RETARDERS BORAX (UP TO 2%)

20. SETTING EXPANSION IS MEASURTED USING AN EXTENSOMETER.
TWO TYPES
 NORMAL SETTING EXPANSION
 HYGROSCOPIC SETTING EXPANSION .

21. ALL GYPSUM PRODUCT SHOW A LINEAR EXPANSION
DURING SETTING , DUE TO THE OUTWARD THRUST OF
THE GROWING CRYSTAL DURING SETTING.
CRYSTAL GROWING FROM THE NUCLEI NOT ONLY
INTERMESH BUT ALSO INTERCEPT EACH OTHER DURING
GROWTH.

22.  WHEN A GYPSUM PRODUCTIS PLACED UNDER WATER
BEFORE INITIAL SET, A GREATER EXPANSION IS SEEN , THIS IS
DUE TO HYGROSCOPIC SETTING EXPANSION.
WHEN EXPANSION BEGINS, EXTERNALLY AVAILABLE
WATER IS DRAWN INTO PORES FORMING IN SETTING MASS.
IT IS GREATER IN MAGNMITUDE THAN NORMAL SETTING
EXPANSION.

23. IMPORTANCE: USE TO EXPAND
SOME GYPSUM BONDED
INVESTMENT.
STRENTH : THE STRENTH
INCREASES RAPIDLY AS THE
MATERIAL HARDENS AFTER THE
INITIAL SETTING.
FACTORS:
FACTORS:
THE MORE WATER , TE GREATER
THE POROSITTY & LESS RTHE
STRENTH .
SPATULATION– WITHIN LIMITS ,
STRENTH INCREASES WITH
INCREASED SPATULATION.
ADDITION OF ACCELERATOR &
RETARDER.