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ISO 20749-2017 pdf free download
ISO 20749-2017 pdf free download.Dentistry Pre-capsulated dental amalgam
Médecine bucco-dentaire — Amalgaine den taire en capsules prédosées.
Repeat this procedure, packing amalgam from the other nine capsules into each of the other nine holes to produce a total of 10 test-pieces. (Dental amalgam from one capsule only is to be used to fill a hole and make a test-piece.) For each test-piece, record the time at which it is made. For all test-pieces, the same surface of the mould should be placed in contact with the glass plate during production. The surface of the amalgam test-piece formed in contact with the glass plate is the “test surface, being the surface on which microhardness indentations will be made.
Immediately after the tenth test-piece has been made, place the mould in the air oven or incubator that is maintained at (37 ± 2) °C and store for (23 ± 1) h.
If a mould of the type shown in Figure 1 Is used, all test-pieces are contained in this single mould and are made over a period of time. Because this mould is put in the oven when the last test-piece has been made and held there for (23 ± 1) h, ensure that the period of time over which the 10 test-pieces are made results in ageing of both the first and the tenth test-piece that complies with the ageing time. Thus, there should be the minimum of delay between packing each test-piece.
At the end of the storage period, remove the mould from the oven, The formation of a test surface with an orange-peel appearance at a microscopic level Is a consequence of the setting reaction and this makes the definition of the hardness indentation unclear. To form a surface suitable for microhardness measurement, gently rub the test surface (i.e. of the mould and the 10 test-pieces it contains) on coated abrasive that complies with microgrit size P 1200, according to Iso 6344-1. Use a copious flow of cold water as a coolant and lubricant, together with a light pressure. The required surface is flat with very fine parallel scratches. Inspect the surface between passes until this is created.
NOTE This surface can be achieved with just four or five passes.
Blow compressed air on the test surface to dry it. For the time remaining before hardness measurement, place the mould on the bench with the test surface upwards and allow the test-piece to equilibrate with the ambient test temperature 1(23 ± 2) °C1.
6.6.5 Microhardness measurement
At (24 ± 1) h, measure the microhardness on the test surface for each of the 10 test-pieces.
Make these measurements at a room temperature of (23 ± 2) °C.
Use a load that will produce an indentation that, when measured to the accuracy of the instrument, will differentiate between dental amalgam products for which the hardness differs by 50 MPa. Use the same load for all products. Use a dwell time that is consistent.
NOTE I For example: For the Vickers hardness of dental amalgam at 24 h,an applied load between 0,5 kgfand
1 kgf is suitable and recommended. Such loads produce indentations with diagonal lengths between 79 pm and
120 pm, depending on the product and applied load. A 50 MPa difference in Vickers hardness value results in a
difference in the Indentation diagonal length of between 1 pm and 3 pm. An instrument with a measurement
accuracy of 0,1 pm is recommended.ISO 20749-2017 pdf free download.
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