MDS PREP
What is the primary function of the eugenol in zinc oxide-eugenol cement?
1) To provide antimicrobial properties
2) To act as a plasticizer
3) To initiate the setting reaction
4) To increase the compressive strength
The eugenol in zinc oxide-eugenol cement acts as a plasticizer, providing temporary softness for easier manipulation.
How does the elastic range of a wire affect its ability to be activated in orthodontic appliances?
1) A high elastic range allows for greater activation without causing permanent deformation.
2) A low elastic range allows for more precise and controlled activation.
3) The elastic range does not affect wire activation; it is only dependent on the force applied.
4) A wire with a high elastic range is more prone to permanent deformation during activation.
The elastic range of a wire determines the extent to which it can be deflected and still return to its original shape without permanent deformation. A wire with a high elastic range can be activated to a greater extent before it reaches its plastic range, making it suitable for larger tooth movements.
What is the effect of adding potassium sulfate to gypsum-based materials?
1) It accelerates the setting reaction.
2) It retards the setting reaction.
3) It increases the porosity.
4) It has no effect on the setting reaction.
Potassium sulfate acts as an accelerator by increasing the solubility of the hemihydrate and promoting the formation of dihydrate, which speeds up the setting process.
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.
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
What is the composition of Cermet Cement?
1) Glass and polyacrylic acid
2) Glass metal powder and polyacrylic acid
3) Zinc oxide and eugenol
4) Calcium hydroxide and polyacrylic acid
Cermet Cement is composed of glass metal powder that is sintered to polyacrylic acid to form a high-density material.
Porcelain binds to metal in PFM crown by:
1) Metallic bind
2) Mechanical bond
3) Chemical bond
4) Both 2 and 3
Dental Materials Answer: 4
Porcelain binds to metal in metal ceramic restorations by mechanical interlocking and chemical bonding. Mechanical interlocking is provided by proper wetting of the metal surface by porcelain.
The adherent metallic oxides, which are formed during the degassing cycle form a good chemical bond with porcelain.
Tin oxide and Indium oxide are formed from precious metal alloys while chromium oxide is formed from base metal alloys.
The elastomeric impression material commonly supplied as a base paste & a liquid catalyst is :
1) Polysulfide
2) Condensation silicone
3) Addition silicone
4) Polyether
Dental Materials Answer: 2
The condensation silicone impression materials are supplied as a base paste and a low-viscosity liquid catalyst (or a paste catalyst).
Putty is a high-viscosity material that has been developed in order to overcome the large polymerization shrinkage of the condensation silicone impression materials.
All the other impression materials are generally supplied as catalyst paste & base paste.