MDS PREP
Which of the following is not true about casting gypsum-bonded investment material?
1) Its used for cast metal alloys
2) 50—65% of gypsum changes to form α-hemihydrate
3) The investment material is not heated above 700°C temperature
4) Heating above 700°C causes formation of sulphur dioxide from copper sulphate
Dental Materials Answer: 1
Gypsum-bonded investments are used for gold alloys. The essential ingredients of the dental inlay investment employed with the conventional gold casting alloys are α-hemihydrate of gypsum, quartz or cristobalite. which are allotropic forms of silica.
Ist investments flow contain the α-hemihydrate of gypsum. because greater strength is obtained. This gypsum
product serves as a binder to hold other ingredients together and provide rigidity. The strength of the investment is dependent on the amount of binder present.
A slight expansion takes place between 400°C and approximately 700°C (1292°F). and then a large contraction occurs. This later shrinkage is most likely caused by decomposition and release of sulphur gases, such as sulphur dioxide.
This decomposition not only causes shrinkage but also contaminates the casting with the sulphides of the nonnohlc alloying elements, such as silver and copper. Thus, it is imperative that gypsum investments should not be heated above 700°C (1292°F). however, for gypsum products containing carbon, the maximum temperature should be 650°C (1202°F). In this way, proper ut and uncontaminated alloys are obtained.
What is the typical film thickness for a resin cement?
1) 50 µm
2) 25 µm
3) 15 µm
4) 5 µm
Resin cements are generally applied in a film thickness of 25 µm or less for optimal performance.
What are the general ideal requirements for a temporary restorative material?
1) High compressive strength and good thermal conductivity
2) Low compressive strength and good thermal conductivity
3) High compressive strength and good marginal sealing
4) Low compressive strength and good marginal sealing
Temporary restorative materials should have low compressive strength (less than 35 MP1) and good marginal sealing to facilitate easy removal and minimize thermal microleakage.
Which type of composite has a filler particle size of 8-12 µm?
1) Microfilled composite
2) Small particle composite
3) Conventional composite
4) Hybrid composite
Conventional composites have a filler particle size of 8-12 µm. Microfilled composites have smaller particles (0.04-0.4 µm), small particle composites have intermediate sizes (1-5 µm), and hybrid composites have even smaller sizes (0.1-0.01 µm).
What is the maximum allowable level of mercury in the blood?
1) 0.5 µg/L
2) 3 µg/L
3) 5 µg/L
4) 10 µg/L
The maximum allowable level of mercury in the blood is 3 µg/L according to the given text.
What is the typical setting time for a high strength dental stone?
1) Less than 10 minutes.
2) 10-30 minutes.
3) 30-60 minutes.
4) More than 60 minutes.
High strength dental stones typically have a setting time of 30-60 minutes, which allows for sufficient working time while providing enhanced mechanical properties.
Nitinol has the disadvantage of which of the following?
1) It cannot be formed into desired shapes
2) It lacks elastic properties
3) Its strength is not suited for orthodontic purposes
4) It lacks stiffness
Dental Materials Answer: 1
Nitinol is a metal alloy – or mixture – of nickel and titanium. This type of wire is also known as “memory wire” or “smart wire,” and it can be used for braces.
What are the stoichiometric formulas for the gamma (?), epsilon (?), and zeta (?) phases in dental amalgams?
1) ?: Ag3Sn, ?: Cu3Sn8, ?: Cu3Sn
2) ?: Ag3Sn, ?: AgSn, ?: CuSn
3) ?: AgSn, ?: Cu3Sn, ?: Ag3Sn8
4) ?: AgSn, ?: CuSn, ?: Ag3Sn.
?: Ag3Sn, ?: Cu3Sn8, ?: Cu3Sn