MDS PREP
What is the primary difference between the setting mechanism of light-cured and chemically cured composite resins?
1) Light-cured resins shrink towards the external surface, while chemically cured resins shrink towards the center.
2) Chemically cured resins require light activation.
3) Light-cured resins require a chemical catalyst.
4) There is no significant difference in the setting mechanism.
The setting mechanism of light-cured resins involves free radical polymerization initiated by light, which causes the material to contract away from the light source (typically the external surface).
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 primary cause of delayed expansion in zinc-containing low-copper or high-copper amalgams?
1) Contamination by oxygen during trituration.
2) Contamination by water during trituration or condensation.
3) Over-trituration.
4) The presence of the ?2 phase.
A large expansion can take place if the amalgam is contaminated by moisture during trituration or condensation, known as delayed expansion or secondary expansion.
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.
The impression for a diagnostic cast of a partial edentulous mouth should be taken in:
1) Impression wax
2) Modelling compound
3) Hydro-colloid
4) Hydro cal
Dental Materials Answer: 3
For making impressions of edentulous ridges, impression plaster and impression compound are considered to be useful. For partial edentulous mouth impressions, hydrocolloids are useful.
What are the main components of a typical dental composite resin?
1) Monomers, fillers, initiators, and accelerators.
2) Resins, fillers, catalysts, and diluents.
3) Polymers, pigments, and plasticizers.
4) Monomers, fillers, and cross-linking agents.
Dental composite resins typically consist of a resin matrix (monomers), filler particles (such as silica or glass), initiators (like camphorquinone), and accelerators (such as amines) to control the setting process.
What is the typical depth of corrosion for most amalgam alloys?
1) 50 to 100 µm
2) 100 to 500 µm
3) 500 to 1000 µm
4) 1000 to 2000 µm
The average depth of corrosion for most amalgam alloys is 100 to 500 µm.
What is the significance of the load deflection rate in orthodontic wires?
1) Low load deflection wires are preferred for large tooth movements.
2) High load deflection wires are preferred for large tooth movements.
3) The load deflection rate does not affect wire selection.
4) The load deflection rate determines the force applied during wire bending.
In orthodontics, wires with a low load deflection rate are typically preferred for areas requiring large tooth movements because they provide a more constant force as the tooth moves and the appliance is deactivated. This constant force is beneficial for controlling the rate of tooth movement.