MDS PREP
What is the typical particle size of silica in microfilled composites?
1) 0.5-1 µm.
2) 0.04-0.2 µm.
3) 1-10 µm.
4) 10-30 µm.
Microfilled composites have a very high surface area with silica particles diameters of 0.04 to 0.2 µm, which provides excellent aesthetic results and polishability.
What is the Threshold Limit Value (TLV) for mercury vapor exposure set by OSHA?
1) 0.01 mg/m3
2) 0.02 mg/m3
3) 0.05 mg/m3
4) 0.1 mg/m3
The TLV for mercury vapor set by OSHA is 0.05 mg/m3.
Addition of carbon is contraindicated in which of the following investment materials :
1) Gypsum bonded
2) Silica bonded
3) Phosphate bonded
4) All
Dental Materials Answer: 3
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.
What is the typical mixing time for temporary cementing materials?
1) 1-5 minutes
2) 5-15 minutes
3) 15-30 minutes
4) 1-15 minutes
The text does not specify the exact mixing time for temporary cements, but it states that the mixing time for all three varieties is approximately 1-15 minutes.
What is the typical range of water to powder ratio for dental stone?
1) 0.28-0.30.
2) 0.40-0.45.
3) 0.45-0.50.
4) 0.50-0.60.
Dental stone typically has a lower water to powder ratio compared to other gypsum products, which gives it higher strength and durability suitable for making dental models.
What is the function of benzoyl peroxide in the composition of denture base resin powder?
1) It acts as a filler
2) It acts as a cross-linking agent
3) It acts as an initiator
4) It acts as an inhibitor
Benzoyl peroxide in the powder of denture base resin is responsible for initiating the polymerization process when it reacts with the monomer in the liquid component.
What is the effect of trituration time on the dimensional change of spherical amalgam alloys?
1) It increases with increased trituration time.
2) It decreases with increased trituration time.
3) It is not affected by trituration time.
4) It is greatest at normal trituration time.
Compressive and tensile strengths of spherical alloys are greatest at normal trituration time.
The opacity in ceramics is achieved by adding
1) Boric oxide
2) Copper oxide
3) Silica
4) Titanium oxide