MDS PREP
What is the typical setting expansion of a high expansion dental stone?
1) Less than 0.1%.
2) 0.1-0.2%.
3) 0.2-0.3%.
4) More than 0.3%.
High expansion dental stones are designed to expand more than typical dental stones to compensate for the contraction of other materials and ensure a precise fit for restorations.
What is the primary function of a base material in dental restoration?
1) To seal the tooth from microleakage
2) To provide insulation from thermal changes
3) To reinforce the tooth structure
4) To enhance the aesthetics of the restoration
A base material in dental restoration is primarily used to provide a seal against microleakage.
A wax pattern made in the mouth will shrink appreciably as it is cooled to room temperature because :
1) The thermal expansion coefficient of wax is very high
2) The thermal expansion coefficient of wax is very low
3) Melting temperature is very high
4) Melting temperature is very low
Dental Materials Answer: 1
A wax pattern made in the mouth will shrink appreciably as it is cooled to room temperature because the coefficient of thermal expansion of wax is very high.(This is the property which describes the thermal energy transport in watts per second through a specimen 1cm thick with a cross sectional area of 1 cm2 when the temperature differential between the surfaces of the specimen perpendicular to the heat flow 10 K) Co efficient of thermal expansion is defined as the change in length per unit of the original length of a material when its temperature is raised 10K.
What is the effect of increasing the concentration of the amine initiator in a light-cured composite?
1) It decreases the depth of cure.
2) It increases the depth of cure.
3) It has no effect on the depth of cure.
4) It can lead to premature polymerization.
An excessive amount of amine initiator can lead to a faster reaction rate and a decrease in the depth of cure, as the light may not be able to penetrate deep enough into the material to activate the entire polymerization process.
What is the primary function of a retarder in gypsum-based dental materials?
1) To accelerate the setting reaction.
2) To enhance the mechanical properties.
3) To prolong the working time.
4) To improve the dimensional stability.
Retarders in gypsum-based materials slow down the setting reaction by forming an adsorbed layer on hemihydrates, allowing more time for manipulation and placement before the material sets.
Which of the following is not a type of temporary cementing material?
1) Zinc oxide-eugenol (type III)
2) Calcium hydroxide
3) Glass ionomer cement (type 1)
4) Resin-modified glass ionomer cement
Resin-modified glass ionomer cement is not listed as a type of temporary cementing material in the text.
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 constituent used in porcelain that fuses at high temperature to form matrix
1) Soda ash
2) Feldspar
3) Quartz
4) Koalin
Dental Materials Answer: 3