Dental waxes and investment materials
Answer the following questions and hand in your report as a group (typed not
• In this picture you can see strips of red wax
o Mention two uses of this type of wax? (2 marks)
1-To adapt the periphery of the impression trays.
2- Used to cover sharp brackets and wires in orthodontic appliances.
• The adjacent strip of wax is called boxing wax (2 marks)
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o What is the wax used for ?
-It is used to form the base portion of a gypsum model .
o What is the recommended storage condition for this wax so that it can be used
- It should be stored in a dry place , slightly below room temperature.
• Which category does this wax belong to? (1 mark)
- Sticky wax which is one of the processing waxes.
• Name one use for this wax in the lab. (1 mark)
- Used to adhere components of metal, gypsum and resin during
fabrication and repair.
o Melting temperature slightly lower than mouth temperature is preferred for bite
registration wax, TRUE OR FALSE? (1 mark)
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• How is expansion achieved in investment materials (3 marks)
- The compensation expansion is achieved by a combination of setting expansion,
thermal expansion and the expansion which occurs when silica undergoes inversion at
elevated temperatures. Hygroscopic expansion can also be used to supplement the
setting expansion of gypsum-bonded materials.
• What are main disadvantages of silica bonded investment. (2 marks)
- Casting temperature and type of alloy to be casted. Also Silica bonded materials are
rarely used nowadays due to the fact that they are less convenient to use than other
products and that the ethanol produced in their liquid can spontaneously ignite or
explode at elevated temperatures. Also The silica-bonded materials are so closely
packed that they are virtually porosity-free and there is a danger of "back pressure"
building up which will cause the mould to be incompletely filled or the casting to be
Question 6. Name three sources of dental wax. (3 marks)
-Plants (e.g. carnauba wax).
-Minerals (e.g. paraffin wax).
-Animals or insects (e.g. beeswax).
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