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1 Dental Materials
What is the maximum allowable dimensional change for amalgams according to ANSI/ADA Specification No. 1?
1) Not more than 10 µm/cm.2) Not more than 20 µm/cm.3) Not more than 30 µm/cm.4) Not more than 40 µm/cm.
The specification requires that amalgam neither contract nor expand more than 20 µm/cm.
2 Dental Materials
What is the most corrodible phase in the low-copper amalgam system?
1) Sn7. Hg2) ? (gamm1) phase3) Cu3Sn phase4) ? (delt1) phase
The Sn7. Hg or ? (gamm1) phase is the most corrodible in the low-copper amalgam system.
3 Dental Materials
What is the dough-forming time for denture base resin according to ANSI/ADA Specification No. 12?1) Less than 10 minutes2) Less than 5 minutes3) Less than 20 minutes4) Less than 30 minutes
ANSI/ADA Specification No. 12 requires that the material should reach a doughlike consistency in less than 10 minutes from the start of the mixing process.
4 Dental Materials
Addition of carbon is contraindicated in which of the following investment materials :
1) Gypsum bonded 2) Silica bonded 3) Phosphate bonded 4) All
Occurence of carbon contamination from investment can easily be observed in case casting temp. are high as seen in melting of high noble alloys for metal ceramic (eg. AgPd or Pd-Ag alloys) or base metal alloys.
Such contamination embrittles the alloy.
5 Dental Materials
What is the purpose of adding barium sulfate to Gutta Percha?1) To make it more radio-opaque2) To improve thermal conductivity3) To enhance the setting reaction4) To act as a plasticizer
Barium sulfate is added to Gutta Percha to enhance its radiographic visibility.
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