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 concentration range for an amine initiator like DMAEMA in a dental composite resin?
1) 0.1-0.2 wt%.
2) 0.5-1.0 wt%.
3) 1-2 wt%.
4) 2-5 wt%.
An aliphatic amine like DMAEMA is used at low concentrations (around 0.15 wt%) in composite resins to initiate the free radical polymerization in the presence of the light-sensitive initiator, such as camphorquinone.
What is the recommended force for condensing a composite resin using a 0.5 mm diameter condenser nib?
1) 3.75 pounds
2) 8.43 pounds
3) 15 pounds
4) 0.04-0.4 µm
The recommended force for condensing a composite resin using a 0.5 mm diameter condenser nib is 3.75 pounds. This force is considered optimal and is well within the physiologic limits of the tooth.
Quartz in investment material is added for
1) Increasing the strength of the investment
2) Acts as binder that binds refractory particlesm
3) Expansion compensation for casting shrinkages by inversion
4) All of the above
Dental Materials Answer: 3
The point at which a stress of a material exhibits a specific limited deviation P Is called
1) Proportional limit
2) Tensile strength
3) Ultimate strength
4) Yield strength
Dental Materials Answer: 4
Yield strength is the stress required to produce plastic deformation.
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 primary function of a dental sealer in restorative procedures?
1) To prevent microleakage
2) To desensitize the tooth
3) To enhance the aesthetics of the restoration
4) To reinforce the tooth structure
A dental sealer is used to fill the microscopic spaces between the restorative material and the tooth structure, primarily to prevent microleakage.
What is the purpose of using temporary cementing materials in dentistry?
1) To permanently fix the prosthesis
2) To allow for temporary fixation of a prosthesis for patient approval
3) To provide a long-term seal against microleakage
4) To strengthen the tooth structure
Temporary cementing materials are used for trial of the temporary appliance for a few days to get patient approval and to ensure it has suitable consistency and can be easily dislodged during permanent cementation.