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.
Investment materials and lost wax casting/ online orthodontic courses
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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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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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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18. Thank you
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