INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com
www.indiandentalacademy.com
www.indiandentalacademy.com
The principal laboratory technique of making
metal inlays, onlays, crowns and bridges, is
based on casting practice. This ...
This process of casting involve some basic steps:
1. Preparation of a wax pattern.
2. Preparation of mold - pour the mixed...
www.indiandentalacademy.com
www.indiandentalacademy.com
Investing:
The process of covering, enveloping, wholly (or) in part an
object such as denture, tooth, wax form, crown, etc...
Allotropic phase:
Phases of similar composition but different
crystallographic structures, with different properties.
Cast...
Easy manipulation.
Good flow.
Detailed reproduction.
Fine particle size to ensure a smooth surface on the casting.
The mix...
At higher temperatures:
It should be stable without any decomposition of
investment.
Should show sufficient expansion enou...
Should wet the surface of the wax pattern properly.
Should be compatible with wax pattern, casting alloys or
castable cera...
www.indiandentalacademy.com
INVESTMENTS USED IN MAKING MOLD FOR
ACRYLIC DENTURES
PLASTER OF PARIS
DENTAL STONE
HYDROCOLLOID (GLYCERIN MODIFIED AGAR)
I...
INVESTMENTS USED FOR CASTING BASE METAL
ALLOYS
PHOSPHATE BONDED INVESTMENT
TYPE I (INLAYS & CROWNS)
TYPE II (RPD FRAMEWORK...
INVESTMENTS USED FOR CASTING CPTI AND
TITANIUM ALLOYS
Phosphate-bonded investments
Ammonia free PBI
Zircon (ZrO2.SiO2) coa...
www.indiandentalacademy.com
BASIC STRUCTURE OF INVESTMENTS:
INVESTMENT MATERIALS CONSIST OF A
REFRACTORY AND A BINDER.
REFRACTORY:
Resists high temper...
The refractory is one or more of the forms of silica,
usually quartz or cristobalite in powdered form. When
heated the for...
The amount of expansion and the temperature
at which it occurs depends on the type and
amount of silica used in the invest...
Binder:
Binds the refractory particles
Provides strength and rigidity to investment
www.indiandentalacademy.com
Gypsum-bonded investments consist of gypsum
products (autoclaved calcium sulphate
hemihydrate, α-form) as the binder, whic...
Phosphate-bonded investment materials consist of
ammonium phosphate and magnesium oxide as the
binder. On setting magnesiu...
Additives:
Modifiers such as boric acid and sodium chloride are
added to regulate the setting time and expansion.
Reducing...
Liquid:
Some investment materials are marketed with an
accompanying high-expansion liquid, which
either replaces water or ...
www.indiandentalacademy.com
Setting time:
The setting time of these investments is dependent
upon the gypsum content and upon the type of
gypsum emplo...
According to ADA specification no.2, the setting time
should neither be shorter than 5 minutes nor longer than 25
minutes....
No much change in setting time when water between 0 C (32F) and
50 C (120 F) is used, but increased more than 50 C (120 F)...
Compressive strength:
In practice it is the compressive strength of the
investment material at the casting temperature tha...
It appears both from laboratory testing and practical
experience, that the majority of the materials on the
market are sat...
Expansion:
The linear casting shrinkage of gold alloys
will vary from one alloy to another, but it will
not be less than 1...
There are three possible ways by which this may be
done:
a) By setting expansion
b) By hygroscopic expansion
c) By thermal...
NORMAL SETTING EXPANSION IS THE
EXPANSION THAT OCCURS DIRECTLY
AFTER MIXING AND PRIOR TO IMMERSION
IN WATER OR HEATING. IT...
Hygroscopic expansion occurs if the investment is allowed
to set in contact with water. It is of two types:
That achieved...
Thermal expansion occurs on heating the
investment through burnout of the wax pattern and
to the temperature at which molt...
Permeability:
This is necessary to allow the air to pass out as
the molten metal enters the mould space. The
greater the p...
If all the particles are of equal sizes, the
permeability will be greater than that of a
mixture of large and small sizes....
Phosphate and gypsum-bonded investments are
more porous as compared to the silicate-bonded
investments. [As the silicate-b...
Expansion of investments:
This is an anomalous use of the word
expansion because gypsum products, without
refractory, cont...
Between 400°c and 700°c a slight expansion
occurs and above 700°c the materials shrinks
severely as it decomposes. Gypsum ...
Normal Setting Expansion:
Normal setting expansions are seen in Gypsum-
bonded (0.06-0.6%) and Phosphate-bonded (0.5%)
inv...
• Lower the Water/Powder ratio greater is the
expansion
• Longer the Mixing time within the practical
limits, greater is t...
No setting expansion will occur with any of
the investment materials bonded with ethyl
silicate. In certain materials of t...
Hygroscopic Setting Expansion:
If the material is allowed to set in contact with
water a greater expansion occurs. This is...
Hygroscopic expansion is inversely
proportional to the percentage of silica in the
investment.
Finer the silica particle s...
•The magnitude of hygroscopic expansion is directly
proportional to the amount of water added during the
setting.
•Reduced...
The common method of obtaining hygroscopic
expansion is to immerse the ring filled with
investment into water at 37 C, at ...
Thermal expansion:
Thermal expansion occurs during the heating
period, first when the wax is being eliminated,
and subsequ...
The water/powder ratio of the mix. Greater the
water/powder ratio lesser is the expansion.
The proportion of silica in the...
www.indiandentalacademy.com
When Gypsum alone is heated it expands slightly up to
118C but then contracts markedly, as much as 2 % at
600C. If the sil...
With quartz owing to its higher inversion
temperature, the optimum thermal expansion does
not occur until approximately 65...
If cristobalite is used the expansion takes place at a
lower temperature and to a greater degree.
Expansions of 1.2 % may ...
Whatever type of investment is used, the heating of the
ring must be gradual to obtain the maximum thermal
expansion.
Ther...
www.indiandentalacademy.com
www.indiandentalacademy.com
Hydrocolloids:
Fluid resin technique (Shepard and Winkler 1967). Makes
use of hydrocolloid as investment material. The wax...
Fluid resin is mixed and poured into the mold
via the sprue openings (28 ml powder of 13 ml
of liquid). Then filled flask ...
Advantages:
1) Better tissue fit
2) Fewer open bites
3) Less fracture of porcelain teeth during deflasking
4) Decreased ma...
Disadvantages :
1) Air Inclusions
2) Shifting of teeth
3) Decrease in occlusal vertical dimension
4) Occlusal imbalances
5...
Gypsum Investment:
They are used in investment of conventional heat and cold cure
dentures, and also in fluid resin dentur...
INVESTMENTS FOR GOLD ALLOYS:
The materials are supplied in the form of powder,
which is mixed with water. The binding agen...
In addition to silica there may be incorporated
small amounts of reducing agents such as
carbon, which produce a reducing ...
When these substances are heated to
temperature known as their “inversion points”,
they undergo an inversion from the α-fo...
www.indiandentalacademy.com
www.indiandentalacademy.com
ADA 2
Type I - For inlay and crown (thermal expansion)
Type II - For inlay and crown (hygroscopic)
Type III – RPD framewor...
However cobalt-chromium alloys with lower melting
points around 1260oc are used, then gypsum bonded
investments of the typ...
WHEN HEATED TO 130-200 C,
(CaSO4)2.H2O  CaSO4
WHEN HEATED TO 200-1000 C,
Hexagonal Anhydrate  Orthorhombic Anhydrate
www...
www.indiandentalacademy.com
www.indiandentalacademy.com
INVESTMENTS FOR BASE-METAL ALLOYS:
They must withstand temperatures of the order of
1000 C without cracking or distortion....
www.indiandentalacademy.com
PHOSPHATE-BONDED:
This investment material is essentially a powder containing
the silica refractory, a soluble acid phosph...
On heating:
Undergoes dehydration at 160 C,
NH4MgPO4.6H2O  NH4MgPO4.H2O + 5H2O
And decomposition between 300 C and 650 C,...
www.indiandentalacademy.com
www.indiandentalacademy.com
SILICATE-BONDED:
1.Binder based on sodium silicate:
This can be used for dip or spray coating for wax
patterns. An aqueous...
Ethyl silicate is a colorless liquid, of specific
gravity 1.06, insoluble in water but soluble in
alcohol and other organi...
This can be brought about by addition of a small
amount of dilute hydrochloric acid to a mixture of
ethyl silicate, indust...
The addition of hydrochloric acid is necessary in order to
accelerate the hydrolysis. Solution, such as that above, are
pr...
THE MECHANISM OF THE SET IS AS FOLLOWS:
Hydrolysis of the solution is commenced by the addition
of the acid and if the sol...
The end products are soft silica gel and ethyl alcohol; on
subsequent heating of the ring, water and alcohol are
driven ou...
However in order to obtain good surfaces on the castings
some fine grade must be used and it is recommended that
70% coars...
www.indiandentalacademy.com
www.indiandentalacademy.com
INVESTMENTS FOR CASTING TITANIUM:
There are various investments on the market for casting
titanium. Phosphate-bonded inves...
In some cases the metal is cast into a mould at
room temperature. In this case, all the expansion
of the mould must be ach...
Recently a new investment material for
titanium casting has been developed, which
contains calcia (cao2) as refractory and...
www.indiandentalacademy.com
www.indiandentalacademy.com
This is a the recently developed investment
for casting titanium inlay, crown and bridge.
Binder — calcia
Refractory —Zirc...
There are 2 types of CaO and mixing liquid.
1. Saturation type (total expansion 2 ± 3%)
2. Delayed expansion type
Properti...
www.indiandentalacademy.com
www.indiandentalacademy.com
Composition:
Powder:
Zirconia (Zr sio4) Mixture
Zirconia flower
Properties:
1. High refractoriness
2. High thermal conduct...
Advantages:
1. Quick casting procedure
2. Increased accuracy of casting
www.indiandentalacademy.com
www.indiandentalacademy.com
www.indiandentalacademy.com
They usually contain phosphate binder and
Mgo /quartz refratories.
1. Magnesia bonded investment
Phosphate binder
Alumin...
2. Phosphate bonded investment:
Phosphate binder
Mgo + Al2O3 →Mgo –Al2O5 (spinel→ highly refractory.)
Show large expansion...
4. Aluminous cement :
(CaO - A12O5 + Mgo (refractory) + 5% Zirconia
Burnout (o)
ZrSio4 ---------------------› Zr↑Expansion...
www.indiandentalacademy.com
(whipmix corporation)
It is a combination of Die stone and gypsum
bonded investment material. The powder is mixed
with col...
Advantages:
The wax pattern and die are invested simultaneously
with out removal of pattern. Useful with gold alloys
Dives...
www.indiandentalacademy.com
ADA Sp No 93
Type I - Gypsum bonded dental brazing investment
Type II - Phosphate bonded.
www.indiandentalacademy.com
www.indiandentalacademy.com
As Prosthodontists, our aim is to make a restoration
as accurate as possible. Most of the restorations
what we are making ...
www.indiandentalacademy.com
Thank you
For more details please visit
www.indiandentalacademy.com
www.indiandentalacademy.com
Upcoming SlideShare
Loading in...5
×

dental investments / academy of fixed orthodontics

261

Published on


Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.

Published in: Education
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
261
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
0
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

dental investments / academy of fixed orthodontics

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. www.indiandentalacademy.com
  3. 3. The principal laboratory technique of making metal inlays, onlays, crowns and bridges, is based on casting practice. This application of casting practice is one of the major advances in restorative dentistry, which is mainly based on “Lost wax technique”. www.indiandentalacademy.com
  4. 4. This process of casting involve some basic steps: 1. Preparation of a wax pattern. 2. Preparation of mold - pour the mixed investment material around the wax pattern and allow it to set. Burn out: wax is eliminated from the investment by boiling (or) burning it in oven. 3. Then casting is done by melting the alloy and forcing the molten metal into the mold cavity. www.indiandentalacademy.com
  5. 5. www.indiandentalacademy.com
  6. 6. www.indiandentalacademy.com
  7. 7. Investing: The process of covering, enveloping, wholly (or) in part an object such as denture, tooth, wax form, crown, etc. with a suitable material before processing, soldering, or casting. 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 temperature) or phosphates and silica (for use in higher casting temperatures). Refractory: Difficult to fuse/corrode, capable of enduring high temperatures. Refractory investment: An investment that can withstand high temperature using a soldering or casting. www.indiandentalacademy.com
  8. 8. Allotropic phase: Phases of similar composition but different crystallographic structures, with different properties. Casting: The act of forming an object in a mold. Something that has been cast in a mold; an object formed by the solidification of a fluid that has been poured or injected into a mold. www.indiandentalacademy.com
  9. 9. Easy manipulation. Good flow. Detailed reproduction. Fine particle size to ensure a smooth surface on the casting. The mixed unset material should have a smooth consistency. Should have sufficient strength: Should exhibit sufficient strength at high temperatures. Inner surface of the mold should not break at a high temperature. Should exhibit sufficient strength, to withstand the force of molten alloy entering the mold. www.indiandentalacademy.com
  10. 10. At higher temperatures: It should be stable without any decomposition of investment. Should show sufficient expansion enough to compensate for shrinkage of wax pattern and solidification of molten metal. The material should be sufficiently porous (permeability) enough to permit escape of air/other gases from the mold cavity during casting of molten metal. It should show ease of divestment: It should not react with metal. It should easily break away (separable) from the surface of casting. www.indiandentalacademy.com
  11. 11. Should wet the surface of the wax pattern properly. Should be compatible with wax pattern, casting alloys or castable ceramics. Should not discolor the casting. Should not be bio-hazardous. Long shelf life. It should be economical. No single material is known that can fulfill all the ideal requirements. So various ingredients/modifiers are added to get the desired properties! www.indiandentalacademy.com
  12. 12. www.indiandentalacademy.com
  13. 13. INVESTMENTS USED IN MAKING MOLD FOR ACRYLIC DENTURES PLASTER OF PARIS DENTAL STONE HYDROCOLLOID (GLYCERIN MODIFIED AGAR) INVESTMENTS USED FOR CASTING GOLD ALLOYS GYPSUM BONDED INVESTMENT TYPE I (THERMAL EXPANSION) TYPE II (HYGROSCOPIC EXPANSION) TYPE III (FOR RPD FRAMEWORKS) PHOSPHATE BONDED INVESTMENT TYPE I (INLAYS & CROWNS) TYPE II (RPD FRAMEWORKS) www.indiandentalacademy.com
  14. 14. INVESTMENTS USED FOR CASTING BASE METAL ALLOYS PHOSPHATE BONDED INVESTMENT TYPE I (INLAYS & CROWNS) TYPE II (RPD FRAMEWORKS) SILICATE-BONDED INVESTMENT SODIUM SILICATE BASED ETHYL SILICATE BASED www.indiandentalacademy.com
  15. 15. INVESTMENTS USED FOR CASTING CPTI AND TITANIUM ALLOYS Phosphate-bonded investments Ammonia free PBI Zircon (ZrO2.SiO2) coated PBI Silicate bonded investments Cemented investments Silica (SiO2) based investments Magnesia (MgO) based investments Zirconia (ZrO2) based investments Alumina (Al2O3) based investments Resin based calcia investment INVESTMENTS USED FOR SOLDERING AND BRAZING PROCEDURES Gypsum-bonded investments Phosphate-bonded investments www.indiandentalacademy.com
  16. 16. www.indiandentalacademy.com
  17. 17. BASIC STRUCTURE OF INVESTMENTS: INVESTMENT MATERIALS CONSIST OF A REFRACTORY AND A BINDER. REFRACTORY: Resists high temperature Provides thermal expansion www.indiandentalacademy.com
  18. 18. The refractory is one or more of the forms of silica, usually quartz or cristobalite in powdered form. When heated the forms of silica undergo displacive transformations, which cause them to expand significantly. This displacive transformation coupled with the setting expansion accounts for the total expansion required, to compensate for the shrinkage of the alloy as it solidifies. www.indiandentalacademy.com
  19. 19. The amount of expansion and the temperature at which it occurs depends on the type and amount of silica used in the investment. www.indiandentalacademy.com
  20. 20. Binder: Binds the refractory particles Provides strength and rigidity to investment www.indiandentalacademy.com
  21. 21. Gypsum-bonded investments consist of gypsum products (autoclaved calcium sulphate hemihydrate, α-form) as the binder, which reacts with water to form calcium sulphate dihydrate. There is no interaction between the refractory (silica) and the binder. www.indiandentalacademy.com
  22. 22. Phosphate-bonded investment materials consist of ammonium phosphate and magnesium oxide as the binder. On setting magnesium oxide reacts with the phosphate ions to produce magnesium ammonium phosphate. In these investments the binder does interact with the surface of the silica particles, which gives, rise to a stronger set material. www.indiandentalacademy.com
  23. 23. Additives: Modifiers such as boric acid and sodium chloride are added to regulate the setting time and expansion. Reducing agents like carbon (graphite) and powdered copper are present in the investment to produce a reducing atmosphere in the investment mould and thus minimize the oxidation of the alloy. Coloring agents may be added to the investments. www.indiandentalacademy.com
  24. 24. Liquid: Some investment materials are marketed with an accompanying high-expansion liquid, which either replaces water or is used in addition to water to control expansion on heating. Such liquids contain alkaline colloidal silica giving them improved strength when set. www.indiandentalacademy.com
  25. 25. www.indiandentalacademy.com
  26. 26. Setting time: The setting time of these investments is dependent upon the gypsum content and upon the type of gypsum employed. It may also be varied by the conditions of mixing. Initial setting times vary between 8 and 15 minutes and final setting times between 12 and 25 minutes. www.indiandentalacademy.com
  27. 27. According to ADA specification no.2, the setting time should neither be shorter than 5 minutes nor longer than 25 minutes. Finer the particle size faster is the set. More the w/p ratio, fewer nuclei per unit volume and hence setting time is prolonged. The longer and the rapidly the material is mixed, the shorter is the setting time. www.indiandentalacademy.com
  28. 28. No much change in setting time when water between 0 C (32F) and 50 C (120 F) is used, but increased more than 50 C (120 F), a gradual retardation occurs. As the temperature reaches 100 C (212 F), no reaction takes place. Accelerators such as potassium sulphate in concentrations higher than 2% produces syngenite [K2Ca(SO4)2.H2O], which crystallizes rapidly. Sodium chloride <2% acts as accelerator but when used >2% it retards the setting reaction. Sodium sulfate < 3.4% acts as accelerator. Retarders such as citrates, acetates and borates are used to prolong the setting time. www.indiandentalacademy.com
  29. 29. Compressive strength: In practice it is the compressive strength of the investment material at the casting temperature that is significant in resisting the possible distortion caused by the inrush of molten alloy. If the material is mixed with a low water/powder ratio (thick mix) then the compressive strength will be increased. www.indiandentalacademy.com
  30. 30. It appears both from laboratory testing and practical experience, that the majority of the materials on the market are satisfactory if used in accordance with the recommended proportions. Compressive strength of PBI type I is 2.5 Mpa and that of type II is 10 Mpa. Compressive strength of ESBI is 1.5 Mpa. www.indiandentalacademy.com
  31. 31. Expansion: The linear casting shrinkage of gold alloys will vary from one alloy to another, but it will not be less than 1.5 per cent and may be as high as 2 per cent. In order that dental castings shall not be that much too small that it is necessary to expand the mould into which they are cast. www.indiandentalacademy.com
  32. 32. There are three possible ways by which this may be done: a) By setting expansion b) By hygroscopic expansion c) By thermal expansion www.indiandentalacademy.com
  33. 33. NORMAL SETTING EXPANSION IS THE EXPANSION THAT OCCURS DIRECTLY AFTER MIXING AND PRIOR TO IMMERSION IN WATER OR HEATING. IT OCCURS DURING THE SETTING OF THE INVESTMENT AND HENCE THE NAME. www.indiandentalacademy.com
  34. 34. Hygroscopic expansion occurs if the investment is allowed to set in contact with water. It is of two types: That achieved by immersing the casting ring in water. That achieved by placing measured amount of water on the investment within the ring. www.indiandentalacademy.com
  35. 35. Thermal expansion occurs on heating the investment through burnout of the wax pattern and to the temperature at which molten metal is cast into the mould. The refractory is responsible for this type of expansion. www.indiandentalacademy.com
  36. 36. Permeability: This is necessary to allow the air to pass out as the molten metal enters the mould space. The greater the proportion of gypsum the less will be the permeability, but the most significant factor in this respect is the uniformity of the particle sizes of the investment. www.indiandentalacademy.com
  37. 37. If all the particles are of equal sizes, the permeability will be greater than that of a mixture of large and small sizes. But greater the permeability of the mould the rougher will be the casting. www.indiandentalacademy.com
  38. 38. Phosphate and gypsum-bonded investments are more porous as compared to the silicate-bonded investments. [As the silicate-bonded investments contain admix of small and large particles and also they are condensed sufficiently to obtain good strength, the porosity decreases.] Graphite in some investments renders more permeability after burnout. www.indiandentalacademy.com
  39. 39. Expansion of investments: This is an anomalous use of the word expansion because gypsum products, without refractory, contract or shrink on heating. Between 200°C and 400°C shrinkage occurs as a result of dehydration. www.indiandentalacademy.com
  40. 40. Between 400°c and 700°c a slight expansion occurs and above 700°c the materials shrinks severely as it decomposes. Gypsum bonded investment can be made to expand sufficiently on heating with the addition of either quartz or cristobalite by counterbalancing the shrinkage of the gypsum binder. www.indiandentalacademy.com
  41. 41. Normal Setting Expansion: Normal setting expansions are seen in Gypsum- bonded (0.06-0.6%) and Phosphate-bonded (0.5%) investments. The casting ring may restrict the expansion, but when the ring is lined with wet absorbent kaolin impregnated paper, the expansion markedly increases. www.indiandentalacademy.com
  42. 42. • Lower the Water/Powder ratio greater is the expansion • Longer the Mixing time within the practical limits, greater is the expansion • Chemical accelerators and Retarders generally reduce the setting expansion www.indiandentalacademy.com
  43. 43. No setting expansion will occur with any of the investment materials bonded with ethyl silicate. In certain materials of this type a contraction of about 0.2% to 0.4% may take place. www.indiandentalacademy.com
  44. 44. Hygroscopic Setting Expansion: If the material is allowed to set in contact with water a greater expansion occurs. This is known as hygroscopic expansion. The extent to which the investment expands hygroscopically varies according to their composition. www.indiandentalacademy.com
  45. 45. Hygroscopic expansion is inversely proportional to the percentage of silica in the investment. Finer the silica particle size of silica greater the expansion. Higher the water content in the original mix, lesser is the hygroscopic expansion. www.indiandentalacademy.com
  46. 46. •The magnitude of hygroscopic expansion is directly proportional to the amount of water added during the setting. •Reduced mixing time decreases the hygroscopic expansion. •Older materials show less expansion. •Greatest amount of expansion is observed if the investment is placed in water before its initial setting. •Less expansion seen when confined to the casting ring. www.indiandentalacademy.com
  47. 47. The common method of obtaining hygroscopic expansion is to immerse the ring filled with investment into water at 37 C, at the initial setting time of the material and allows it to remain there for 30 minutes. A controlled expansion can be obtained by adding measured amount of water on to the surface of the investment, within the casting ring. Hygroscopic expansion of about 0.6 to 0.8 % can be seen in PBI. www.indiandentalacademy.com
  48. 48. Thermal expansion: Thermal expansion occurs during the heating period, first when the wax is being eliminated, and subsequently during the time necessary to reach the temperature suitable for casting to be carried out. The percentage thermal expansion for any material depends upon: www.indiandentalacademy.com
  49. 49. The water/powder ratio of the mix. Greater the water/powder ratio lesser is the expansion. The proportion of silica in the material. When silica content increases the expansion increases. The variety of silica, either quartz or cristobalite. Cristobalite gives more thermal expansion than quartz even at a lower temperature (200 C). www.indiandentalacademy.com
  50. 50. www.indiandentalacademy.com
  51. 51. When Gypsum alone is heated it expands slightly up to 118C but then contracts markedly, as much as 2 % at 600C. If the silica content is increased the expansion of silica counterbalances the thermal contraction of gypsum. But there may be weakening of the investment. The addition of small amounts of modifiers such as sodium, potassium, or lithium chlorides may eliminate the contraction caused by the gypsum. www.indiandentalacademy.com
  52. 52. With quartz owing to its higher inversion temperature, the optimum thermal expansion does not occur until approximately 650-700 C. This means that casting must not be carried out bellow that temperature when using quartz-type investments. www.indiandentalacademy.com
  53. 53. If cristobalite is used the expansion takes place at a lower temperature and to a greater degree. Expansions of 1.2 % may be obtained at 500 C, remaining constant up to 900 C if necessary. This means that the casting temperature range is much less critical if cristobalite is used, than in case of quartz. www.indiandentalacademy.com
  54. 54. Whatever type of investment is used, the heating of the ring must be gradual to obtain the maximum thermal expansion. Thermal expansion of 0.8% is seen in PBI if 50:50 mixtures of liquid and water are used. Thermal expansion may increase to 1.0-1.2% if undiluted liquid is used. In ESBI the thermal expansion may be 1.5 to 1.8% when heated from room temperature to 1000-1177C. www.indiandentalacademy.com
  55. 55. www.indiandentalacademy.com
  56. 56. www.indiandentalacademy.com
  57. 57. Hydrocolloids: Fluid resin technique (Shepard and Winkler 1967). Makes use of hydrocolloid as investment material. The waxed- up denture is sealed and positioned in a specially designed flask. Which is then filled with reversible hydrocolloid investment medium. After gelation of hydrocolloid, the cast with the attached waxed up denture is removed then vents and sprues are cut from outside the flask into the mold space. The wax and base plate are eliminated, then the teeth and the cast are replaced in the vented flask. www.indiandentalacademy.com
  58. 58. Fluid resin is mixed and poured into the mold via the sprue openings (28 ml powder of 13 ml of liquid). Then filled flask is held in a pressurized (0.14 Mpa) chamber at room temperature until the resin cures completely . The set resin is removed and trimmed. www.indiandentalacademy.com
  59. 59. Advantages: 1) Better tissue fit 2) Fewer open bites 3) Less fracture of porcelain teeth during deflasking 4) Decreased material cost 5) Simple processing method. www.indiandentalacademy.com
  60. 60. Disadvantages : 1) Air Inclusions 2) Shifting of teeth 3) Decrease in occlusal vertical dimension 4) Occlusal imbalances 5) Incomplete flow of denture base material 6) Technique sensitive www.indiandentalacademy.com
  61. 61. Gypsum Investment: They are used in investment of conventional heat and cold cure dentures, and also in fluid resin denture preparation Basic reaction of gypsum products Gypsum products used for processing dentures are : Type II, III plaster www.indiandentalacademy.com
  62. 62. INVESTMENTS FOR GOLD ALLOYS: The materials are supplied in the form of powder, which is mixed with water. The binding agent is usually the α-hemihydrate of gypsum. Since it gives a greater crushing strength to the investment; the binder content is usually between 25 and 40 percent by weight. www.indiandentalacademy.com
  63. 63. In addition to silica there may be incorporated small amounts of reducing agents such as carbon, which produce a reducing atmosphere in the investment mould and thus minimize the oxidation of the alloy. Silica may be present in of its forms, quartz or cristobalite. www.indiandentalacademy.com
  64. 64. When these substances are heated to temperature known as their “inversion points”, they undergo an inversion from the α-form to the β-form. This change is accompanied by a marked expansion. The inversion of quartz occurs at 575 c, and of cristobalite at between 200 c and 270 c. www.indiandentalacademy.com
  65. 65. www.indiandentalacademy.com
  66. 66. www.indiandentalacademy.com
  67. 67. ADA 2 Type I - For inlay and crown (thermal expansion) Type II - For inlay and crown (hygroscopic) Type III – RPD framework Cannot be used in conjunction with cobalt chromium alloys whose melting point is approximately 1425 c; decomposition of gypsum takes place in the presence of silica. This causes rapid evolution of oxides of sulphur and consequent porosity and embitterment of casting occurs. www.indiandentalacademy.com
  68. 68. However cobalt-chromium alloys with lower melting points around 1260oc are used, then gypsum bonded investments of the type used for gold casting can be employed. WHEN MIXED WITH WATER, (CaSO4)2.H2O + 3 H2O  2CaSO4.2H2O + HEAT • WHEN HEATED TO 110-130 C, CaSO4.2H2O  (CaSO4)2.H2O www.indiandentalacademy.com
  69. 69. WHEN HEATED TO 130-200 C, (CaSO4)2.H2O  CaSO4 WHEN HEATED TO 200-1000 C, Hexagonal Anhydrate  Orthorhombic Anhydrate www.indiandentalacademy.com
  70. 70. www.indiandentalacademy.com
  71. 71. www.indiandentalacademy.com
  72. 72. INVESTMENTS FOR BASE-METAL ALLOYS: They must withstand temperatures of the order of 1000 C without cracking or distortion. They must have sufficient expansion to compensate for the thermal contraction of the cobalt-chromium alloy, which has been established to be about 2.2 %. www.indiandentalacademy.com
  73. 73. www.indiandentalacademy.com
  74. 74. PHOSPHATE-BONDED: This investment material is essentially a powder containing the silica refractory, a soluble acid phosphate and a metallic oxide. When this powder is mixed with water, the following reaction occurs: NH4H2PO4 + MgO  NH4MgPO4+ H2O OR NH4H2PO4+ MgO +H2O NH4MgPO4.6H2O 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. www.indiandentalacademy.com
  75. 75. 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 Further reaction with excess mgo if heated above 1040 C, Mg2p2o7 + mgo  mg3(p2o4)2 When ammonium magnesium phosphate and silica react to form complex silico-phosphates, it gives greater strength to the investment at higherwww.indiandentalacademy.com
  76. 76. www.indiandentalacademy.com
  77. 77. www.indiandentalacademy.com
  78. 78. SILICATE-BONDED: 1.Binder based on sodium silicate: This can be used for dip or spray coating for wax patterns. An aqueous solution of sodium silicate is acidified by the addition of hydrochloric acid and abounding silicic acid gel is formed. However such investments are not generally used. 2.Binder based on ethyl silicate: Once it was widely used but now used mainly in large laboratories, where its inconvenience of preparation is offset by its lower cost. www.indiandentalacademy.com
  79. 79. Ethyl silicate is a colorless liquid, of specific gravity 1.06, insoluble in water but soluble in alcohol and other organic solvents. Its important chemical property is its ability to undergo hydrolysis to give silicic acid as follows: Si(C2H5O)4 + 4H2O  Si(OH)4 + 4C2H5OH nSi(OH)4+ MgO  MgO[Si(OH)4]n www.indiandentalacademy.com
  80. 80. This can be brought about by addition of a small amount of dilute hydrochloric acid to a mixture of ethyl silicate, industrial spirit and water. 500 ml ethyl silicate 1500 ml industrial spirit 50 ml water 10 ml dil. Hydrochloric acid www.indiandentalacademy.com
  81. 81. The addition of hydrochloric acid is necessary in order to accelerate the hydrolysis. Solution, such as that above, are prepared and allowed to stand for 12 to 24 hours before use. The silica investment powder, which may be quartz or cristobalite or a mixture of the two, is then mixed with the solution and setting takes place, usually within hour after mixing. www.indiandentalacademy.com
  82. 82. THE MECHANISM OF THE SET IS AS FOLLOWS: Hydrolysis of the solution is commenced by the addition of the acid and if the solution is allowed to stand at room temperature for about a week, hydrolysis proceeds to complete gelation and the solution turns into a jelly. If silica powder is added to the solution before this occurs, say 24 hours after adding the acid, then this silica speeds up the hydrolysis, produces gelation and hence the investment sets. www.indiandentalacademy.com
  83. 83. The end products are soft silica gel and ethyl alcohol; on subsequent heating of the ring, water and alcohol are driven out and a hard gel of amorphous silica remains. It has been found that the particle size and shape of the silica powder are important factors in the bonding process. If particles are of uniform size, bonding with the hydrolyzed ethyl silicate solution will not take place. Consequently varying grades of silica powder must be used and their structure should be subangular and porous. www.indiandentalacademy.com
  84. 84. However in order to obtain good surfaces on the castings some fine grade must be used and it is recommended that 70% coarse and 30% fine grade is employed. Above this percentage the mould is liable for crack on heating. www.indiandentalacademy.com
  85. 85. www.indiandentalacademy.com
  86. 86. www.indiandentalacademy.com
  87. 87. INVESTMENTS FOR CASTING TITANIUM: There are various investments on the market for casting titanium. Phosphate-bonded investments have been used but are usually modified forms that give sufficient expansion to compensate for the shrinkage of the metal at lower mould temperatures. To avoid contamination and surface degradation of the casting the mould is heated to a much lower temperatures prior to casting. www.indiandentalacademy.com
  88. 88. In some cases the metal is cast into a mould at room temperature. In this case, all the expansion of the mould must be achieved by setting through the use of high expansion liquids. Other types of materials for casting titanium include alumina- based, spinel-based, zirconia-based and magnesia-based investments. One such magnesia-based investment utilizes magnesia as the refractory and aluminous cement as the binder. www.indiandentalacademy.com
  89. 89. Recently a new investment material for titanium casting has been developed, which contains calcia (cao2) as refractory and cold- cure acrylic resin (PMMA) as binder, known as “resin-bonded calcia investment”. www.indiandentalacademy.com
  90. 90. www.indiandentalacademy.com
  91. 91. www.indiandentalacademy.com
  92. 92. This is a the recently developed investment for casting titanium inlay, crown and bridge. Binder — calcia Refractory —Zirconia www.indiandentalacademy.com
  93. 93. There are 2 types of CaO and mixing liquid. 1. Saturation type (total expansion 2 ± 3%) 2. Delayed expansion type Properties 1. Total thermal and setting expansion found was -1 .5 - 2.5% 2. The maximum thermal expansion is found at - 900 - 1200°c www.indiandentalacademy.com
  94. 94. www.indiandentalacademy.com
  95. 95. www.indiandentalacademy.com
  96. 96. Composition: Powder: Zirconia (Zr sio4) Mixture Zirconia flower Properties: 1. High refractoriness 2. High thermal conductivity 3. Low co-efficient of thermal expansion 4. Low reactivity with molten titanium www.indiandentalacademy.com
  97. 97. Advantages: 1. Quick casting procedure 2. Increased accuracy of casting www.indiandentalacademy.com
  98. 98. www.indiandentalacademy.com
  99. 99. www.indiandentalacademy.com
  100. 100. They usually contain phosphate binder and Mgo /quartz refratories. 1. Magnesia bonded investment Phosphate binder Alumina /Mgo refractories good heat resistance Low thermal expansion www.indiandentalacademy.com
  101. 101. 2. Phosphate bonded investment: Phosphate binder Mgo + Al2O3 →Mgo –Al2O5 (spinel→ highly refractory.) Show large expansion due to spinel reaction. 3. Spondumen (H2O - A12O5 - Sio2) Expand irreversible on heating at 900 - 1100°c www.indiandentalacademy.com
  102. 102. 4. Aluminous cement : (CaO - A12O5 + Mgo (refractory) + 5% Zirconia Burnout (o) ZrSio4 ---------------------› Zr↑Expansion www.indiandentalacademy.com
  103. 103. www.indiandentalacademy.com
  104. 104. (whipmix corporation) It is a combination of Die stone and gypsum bonded investment material. The powder is mixed with colloidal silica. Properties: Setting expansion - 0.9% Thermal expansion - 0.6% (at 977°c) www.indiandentalacademy.com
  105. 105. Advantages: The wax pattern and die are invested simultaneously with out removal of pattern. Useful with gold alloys Divestment phosphate(DVP): Similar to divestment, but used for casting post and core, crowns of base metal alloys without any need of removal of wax pattern. www.indiandentalacademy.com
  106. 106. www.indiandentalacademy.com
  107. 107. ADA Sp No 93 Type I - Gypsum bonded dental brazing investment Type II - Phosphate bonded. www.indiandentalacademy.com
  108. 108. www.indiandentalacademy.com
  109. 109. As Prosthodontists, our aim is to make a restoration as accurate as possible. Most of the restorations what we are making are cast restorations and that is why we should have knowledge about various materials and techniques used in casting a dental restoration. 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. www.indiandentalacademy.com
  110. 110. www.indiandentalacademy.com
  111. 111. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.com

×