Types of investments

1. GOOD
MORNING
1

2. DENTAL
INVESTMENT
MATERIALS
2
Dr.AJAY TEJA
I MDS

3. CONTENTS
 Introduction
 Definitions
 Ideal properties
 General composition
 Types of investment materials
 New investment materials
 Conclusion
 References
3

4. 4
INTRODUCTION

5. DEFINITIONS
 INVESTMENT-material that is suitable for forming a mold
into which a metal or alloy is cast.(GPT-9)
 DENTAL CASTING INVESTMENT-a material consisting
principally of an allotrope of silica and a bonding agent;
the bonding substance may be gypsum (for use in lower
casting temperatures) or phosphates and silica (for use
in higher casting temperatures) (GPT-9)
 INVESTING-the process of covering or enveloping,
wholly or in part, an object such as a denture, tooth, wax
form, crown, etc., with a suitable investment material
before processing, soldering, or casting.(GPT-9)
5

6. IDEAL PROPERTIES:
 Should not react with wax and alloys.
 Should be easily manipulated.
 The inner surface of the mold should not breakdown at
higher temperature.
 At higher temperature, the investment must not decompose
to give off gases that could corrode the surface of the alloy.
 should have enough expansion to compensate for
shrinkage of the wax pattern and the metal that takes place
during the casting procedure.
6

7.  A dental casting investment should be porous enough to
allow the air or other gases in the mold cavity to escape
easily during the casting procedure.
 The investment should produce a smooth surface and fine
detail and margins on the casting.
 Should have long shelf life.
 Should be inexpensive.
 Should have high compressive strength to withstand
impact forces of molten alloy.
7

8. GENERAL COMPOSITION:
 Refractory Material
 Binder Material
 Other Chemicals
8

9. REFRACTORY MATERIAL:
 Material which can withstand high temperature.
 It is a form of silicon dioxide such as quartz,
tridymite,cristobalite and fused quartz.
 Contraction of gypsum can be eliminated.
9

10. SILICA TYPE TEMPERATURE EXPANSION
QUARTZ 5750 C 1.4%
TRIDYMITE 117°C and 163°C 1.0%
CRYSTOBALITE 200°C and 270°C 1.8%
10

11. BINDER:
 form a solid mass with refractory material.
 a-calcium sulfate hemihydrate,
 phosphate,
 ethyl silicate.
11

12. OTHER CHEMICALS:
 sodium chloride, boric acid, potassium sulfate,
graphite, copper powder and MgO
12

13. TYPES OF INVESTMENT
13

14. 1. Based on type of binder present:
a. Gypsum bonded investment: CaSO4 a-hemihydrate
b. Phosphate bonded investment: Monoammonium phosphate
c. Silica bonded investment: Ethyl silicate.
2. Based on refractory material:
a. Quartz investments
b. Cristobalite investments
3. Based on temperature of casting:
a. Low temperature investments
b. High temperature investments.
14

15. GYPSUM BONDED
INVESTMENTS:
ISO / ANSI / ADA :
 Type 1 casting inlays, onlays, crowns, or other
fixed prostheses
 Type 2  removable partial denture frameworks
15

16. COMPOSITION:
Ingredient Wt % Functions
Calcium sulfate α-
hemihydrate
25–45 • Acts as a binder.
• Improves strength
Silica 55–75 • Refractory material and can withstand high
temperatures.
• Regulates the thermal expansion
Modifiers
E.g. Boric acid, NaCl, etc.
Trace • Regulates the setting expansion and setting
time.
• Also prevents most of the shrinkage of
gypsum, when it is heated above 300°C
Reducing agents
E.g. Carbon, powdered
graphite or
powdered copper
Trace • To provide a nonoxidizing atmosphere in the
mold when the gold alloy is cast
Coloring agents Trace • Provides characteristic color
16

17.  200 to 400 °C- it dehydrates and shrinks.
 A slight expansion occurs between 400 and 700 °C,
and a large contraction then takes place at higher
temperatures, caused by decomposition of the
calcium sulfate.
 Thus it is imperative that gypsum investments not
be heated above 700 °C.
17

18. SETTING EXPANSION:
 Dimensional increase that occurs concurrent with the
hardening of various materials such as dental stone,die
stone and dental casting.(GPT-9)
 controlled by retarders and accelerators for the gypsum
 exothermic heat of gypsum setting can result in
expansion of the wax pattern
 If a softer wax is used, the setting expansion may
cause excessive distortion of the pattern
18

19. HYGROSCOPIC SETTING
EXPANSION:
 Expansion as a result of absorption of moisture.(GPT-9)
 six or more times greater than normal SE.
 magnitude of hygroscopic setting expansion is
generally proportional to the silica content.
 Decreased by:
 High w/p ratio.
 Reducing mixing time.
 Immersion of the investment should be delayed.
19

20. STRENGTH:
 use of chemical modifiers increases the strength
because more of the binder can be used without a
marked reduction in thermal expansion
 affected by the W/P ratio
 cooled to room temperature, its strength decreases
considerably, presumably because of fine cracks that
form during cooling
20

21. POROSITY:
 air is not completely expelled, a back pressure builds
up to prevent the molten alloy from completely filling
the mold.
 Thus it is important that the end of a wax pattern that
is nearest to the end of the investment ring not be
covered by more than 6 mm of investment to allow
sufficient interconnectivity of the porous network for
the escape of gas from the mold cavity during filling
of the mold with molten metal.
21

22. STORAGE:
 stored in airtight and moisture-proof containers
22

23. PHOSPHATE
BONDED
INVESTMENTS
23

24. COMPOSITION
POWDER:
 BINDER MgO & NH4H2PO4
 REFRACTORY MATERIALS QUARTZ OR CRISTOBALITE
 CARBON TRACE ELEMENT
LIQUID:
 COLLOIDAL SILICA SUSPENSION
REACTION PRODUCT:
 MONOAMMONIUM DIACID PHOSPHATE OR MAGNESIUM AMMONIUM
PHOSPHATE
 Nh4MgPO4.6H2O
24

25.  This chemical reaction is accompanied by a physical
reaction in which the slurry changes into a solid; this
gives the initial or green strength to the investment.
 On heating: Undergoes dehydration at 160 C,
NH4MgPO4.6H2O → NH4MgPO4.H2O + 5H2O
 And decomposition between 300 C and 650 C,
2NH4MgPO4.H2O → Mg2P2O7 + 3H2O + 2NH3
25

26. WORKING AND SETTING TIME:
 IDEAL– MIX AS LONG AS POSSIBLE
 INCREASE IN L/P  INCREASES WORKING TIME
 MECHANICAL MIXING UNDER VACUUM IS
PREFERRED.
26

27. SETTING AND THEMAL EXPANSION:
 SE WITH COLLOIDAL SILICA
 WITH WATER- SHRINKAGE
 2% COMBINED SE & TE
27

28. ADVANTAGES
 ABILITY TO WITHSTAND HIGH TEMP
 SUFFICIENT GREEN AND FIRED
STRENGTH
 SE &TE SUFFICIENTLY HIGH
DISADVANTAGES:
 > 1375 0 C MOLD BREAKDOWN AND
ROUGH SURFACES OF CASTING.
 DIFFICULT TO REMOVE CASTING FROM
INVESTMENT
28

29. TYPICAL BURN OUT
TEMPERATURES:
 GOLD ALLOYS:700-7500 C
 PALLADIUM SILVER ALLOYS:730-815O C
 BASE METAL ALLOY:815-900O C
29

30. SURFACE QUALITIES
 Increasing the ratio of “special liquid” to water used
for the mix enhances casting surface smoothness
but can lead to oversized castings
30

31. ETYL-SILICATE BONDED
INVESTMENTS
 MORE COMPLICATED AND TIME CONSUMING
 HIGH FUSING BASE METAL ALLOYS
 Binder- silica gel that reverts to silica (cristobalite) on
heating
 Fillers- SILICA & magnesium oxide
 GREEN SHRINKAGE
 1090-180O C…….HIGH FUSING ALLOYS
 ITS LOW SETTING EXPANSION MINIMISES
DISTORTION
 MORE SUITED FOR LARGE PRECISE CASTINGS
31

32. ADVANTAGES:
 HIGH TEMP CO-CR &NI-CR ALLOYS
 GOOD SURFACE FINISH
 LOW DISTORTION &HIGH THERMAL EXP
 EASY TO REMOVAL FROM CASTING
 DISADVANTAGES:
32

33. NEW INVESTMENT
MATERIALS:
 Magnesia and Alumina Based Phosphate-Bonded Investment
Materials.
 Alumina-Based Gypsum-Bonded Investment Materials
 Magnesia-Based Silica-Bonded Investment Materials
 Magnesia-Based Aluminous Cement-Bonded Investment Materials
 Calcia-Based Lost Resin-Bonded Investment Materials
33

34. CONCLUSION
 Investment materials are to be selected based on
the type of restoration, the type of metal or alloy to
be casted, as well as technique used for casting
and that is how we can achieve a better
restoration.

35. References
 Anusavice K.J. –“Phillips’ science of dental materials”
13th edition, 2012
 Craig R.G. & Powers J.M.- “Restorative dental
materials” 11th edition 2001
 Alla RK,Rama Krishna alla dental material science,1st
edition,jaypee,new delhi,2013.
 Dr. Prakhar Khurana, Dr. Romil Singhal, Dr. Samarth
Kumar Agarwal, Dr. Rachna Maheshwari: INVESTMENT
MATERIALS: A REVIEW. ejpmr, 2020,7(7), 457-461

36. THANK YOU
36