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1. Investment Materials and Lost-
Wax Casting
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
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2. Aims & objectives
At the end of this lecture you should
understand:
 The basis of the lost-wax casting process
 The role of investment materials in lost-wax
casting
 The effects of composition on the properties
of investments
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3. Lost wax
casting
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4. Example of a cast implant
superstructures
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5. Casting machines
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6. Cp titanium
- vacuum casting
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7. What do we require of investments?
An investment material to be used for a casting mould should
expand on setting and heating to compensate for the cooling of
the cast metal as it returns to room temperature.
The investment material should be of a suitable consistency for
adaptation to the wax model and have a reasonable setting
time.
To withstand the temperatures required for the casting process
there should be no distortion; no decomposition; the investment
should not fragment or disintegrate under the impact of the
molten metal; the material should be porous to allow the
escape of air and gases and the investment should be easily
removed from the casting after cooling.
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8. Casting errors
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9. What is the role of the refractory
in the investment material?
 A heat resistant material such as silica (SiO2)
 Silica has several allotropic forms
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10. How do we get the investments to
expand to compensate for alloy
shrinkage on cooling?
 Displacive transformations – change of bond angles causing a slight
shift in the relative positions of atoms
 Reconstructive transformations – conversion of one silica form to
another by breaking of bonds which requires much energy and
therefore, does not occur easily.
 Heating expansion – the combined effect of thermal expansion and
displacive expansion.
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11. Typical refractories in dental
investments: quartz & cristobalite
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12. The binder keeps the refractory
particles together.
 For gypsum bonded investments is based on
calcium sulphate hemihydrate (see plaster & stone)
 For phosphate bonded investments (see below)
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13. Heating the gypsum binder alone
without the refractory?
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14. What is the use of
expansion liquid?
 An example of a high expansion liquid is a form of silica sol in
water. In this instance the investment is able to set
hygroscopically.
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15. What are the effects of different
handling techniques?
 hygroscopic expansion
 water to powder ratio
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16. Aluminous cements
are used for cp-Titanium
 Aluminous cements have been developed for casting commercially
pure titanium. They have greater thermal stability and reduce the
interactions between the investment and the casting.www.indiandentalacademy.com

17. Ask yourselves !!
 What three types of expansion have been
considered ?
 What three types of investment have been
discussed ?
 What is the common fourth investment that is
described in dental materials texts, and is still
used, but more infrequently than the other three ?
 Why should investments be porous ?
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