MDS PREP
What is the ideal thickness of a luting agent film for it to be effective?
1) 50 µm
2) 25 µm
3) 10 µm
4) 5 µm
An effective luting agent must be able to flow into a continuous film of 25 µm thickness or less without fragmentation.
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 difference between type I and type II glass ionomer cements?
1) Type I has a higher fluoride release
2) Type II has a higher compressive strength
3) Type I sets faster
4) Type II has better aesthetic properties
Type II glass ionomer cements have a higher compressive strength, while Type I is often used for better aesthetics.
How does the presence of the ?2 phase affect the corrosion resistance of high-copper amalgams?
1) It significantly increases the corrosion resistance.
2) It has no effect on the corrosion resistance.
3) It significantly decreases the corrosion resistance.
4) It is the most corrodible phase in high-copper amalgams.
The ?2 phase is the least corrosion-resistant phase in high-copper amalgams.
What are the typical operating speeds for low-, medium-, and high-speed amalgamators?
1) 3000 to 3200 cpm for low-speed, 3500 to 3700 cpm for medium-speed, and 4000 to 4400 cpm for high-speed.
2) 3200 to 3400 cpm for low-speed, 3700 to 3800 cpm for medium-speed, and 4000 to 4400 cpm for high-speed.
3) 3000 to 3200 cpm for medium-speed, 3500 to 3700 cpm for high-speed, and 4000 to 4400 cpm for low-speed.
4) 3200 cpm for low-speed, 3700 cpm for medium-speed, and 4400 cpm for high-speed.
Low-speed amalgamators operate at 3200 to 3400 cpm, medium-speed at 3700 to 3800 cpm, and high-speed at 4000 to 4400 cpm.
What is the effect of acid etching on dentin bond strength?
1) It decreases bond strength.
2) It has no effect on bond strength.
3) It increases bond strength.
4) It is unpredictable.
Acid etching of dentin creates a micro porous surface that allows for better infiltration and mechanical interlocking of the bonding agent, leading to improved bond strength between the restorative material and the tooth structure.
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.
The function of 2% potassium sulphate in a gypsum product is
1) to regulate the setting expansion.
2) to regulate the setting time.
3) to act as a retarder.
4) none of the above.
Dental Materials Answer: 4
Sodium chloride is an accelerator up to about 2% of the hemihydrates, but at a higher concentration, it acts as a retarder. Sodium sulphate has its maximum acceleration effect at approximately 3.4%; at greater concentrations, it becomes a retarder.
The most commonly used accelerator is potassium sulphate. It is particularly effective in concentrations higher than 2% since the reaction product. which seems to be syngenite (K,Ca[SO4].H1O) crystallizes rapidly. Many soluble sulphates act as accelerators, whereas powdered gypsum (calcium sulphate dehydrate) accelerates the setting rate, because the
particles act as nuclei of crystallization.
Citrates. acetates and borates generally retard the reaction.