Lab3assignment 2013
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Lab3assignment 2013

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    Lab3assignment 2013 Lab3assignment 2013 Document Transcript

    • Dental materials " DENT 203 " Assignment 3 Group 4 Sec 3 20072050289 20110050024 20110050045 20110050051 20110050058 20110050068 20110050070 20110050072 20110050088 20110050095 20110050097 Page | 1
    • Laboratory 3 Dental waxes and investment materials Answer the following questions and hand in your report as a group (typed not hand written) Question 1. • In this picture you can see strips of red wax • Questions: 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. Question 2. • The adjacent strip of wax is called boxing wax (2 marks) Page | 2
    • 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 successfully? - It should be stored in a dry place , slightly below room temperature. Question 3. . • 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. Questions 4. o Melting temperature slightly lower than mouth temperature is preferred for bite registration wax, TRUE OR FALSE? (1 mark) - FALSE. Page | 3
    • Question 5. • 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 porous. 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). Page | 4