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 primary advantage of resin teeth over porcelain teeth in terms of impact resistance and ductility?
1) Resin teeth are more likely to chip or fracture.
2) Resin teeth have better dimensional stability.
3) Resin teeth have greater wear resistance.
4) Resin teeth are less likely to chip or fracture.
Resin teeth are more ductile than porcelain teeth, which means they can absorb and distribute forces better, making them less prone to chipping or fracturing on impact.
What is the primary concern with using zinc oxide-eugenol cement in large restorations?
1) Low compressive strength
2) Potential for pulpal toxicity
3) High thermal conductivity
4) High solubility
The primary concern is the potential for pulpal toxicity due to the diffusion of eugenol.
What happens to the strength of irregularly shaped amalgam alloys when they are over-triturated?
1) It significantly increases.
2) It significantly decreases.
3) It remains the same.
4) It first increases and then decreases.
The strength of irregularly shaped amalgam alloys increases with over-trituration.
What is the role of a primer in the bonding process of resin cements?
1) To clean the tooth surface
2) To increase the surface energy of the tooth structure
3) To reduce the surface tension of the bonding agent
4) To accelerate the setting of the cement
A primer increases the surface energy of the tooth structure, enhancing the ability of the bonding agent to wet and infiltrate the surface.
Epoxy resins are compatible with which of the following impression material :
1) Polysulphide impression material
2) Polyether impression material
3) Agar
4) Alginate
Dental Materials Answer: 2
Epoxy resins
· Abrasion resistance is many times greater than gypsum
· More expensive
· Undergoes 0.1 – 0.2% shrinkage, thus their shrinkage is approximately equal to gypsum. This is less of problem with newer formulations & polyurethane resin.
· Their detail reproduction is better.
· Hydrocolloids, polysulfides are not compatible with them.
What is the primary advantage of using the frozen slab technique with zinc phosphate cement?
1) It increases the working time.
2) It decreases the setting time.
3) It increases the mechanical properties.
4) It changes the pH of the cement.
The frozen slab technique increases the working time of zinc phosphate cement by allowing more moisture to condense on the cool glass slab.
What is the main advantage of using Ormocers in dental restorations?
1) They have a high coefficient of thermal expansion.
2) They have excellent biocompatibility and resistance to masticatory loading.
3) They are easy to manipulate and require minimal finishing.
4) They can be used in high-stress bearing areas without reinforcement.
The main advantage of using Ormocers is their excellent biocompatibility and resistance to masticatory loading. They also have good esthetic properties, resembling those of natural teeth.