MJDF Dental Materials Science 4

Question 1

Which ceramic system is most appropriate for a single-unit anterior crown requiring high aesthetics?

Accepted Answer

Lithium disilicate (e.g., IPS e.max) — excellent translucency and adequate strength for anterior teeth

Answer

Lithium disilicate has superior translucency and aesthetics compared to zirconia, with adequate flexural strength (400 MPa) for single-unit anterior and premolar crowns, making it the preferred system for aesthetic anterior work.

Question 2

What is the working and setting time of addition silicone impression material?

Accepted Answer

Working time: 2–3 minutes; total setting time: 5–6 minutes (varies by viscosity and manufacturer)

Answer

Addition silicone provides a working time of approximately 2–3 minutes and complete setting in 5–6 minutes, allowing adequate time for tray loading, positioning, and seating while ensuring dimensional accuracy.

Question 3

What is the key advantage of ether-based polyether impression material compared to addition silicone?

Accepted Answer

Hydrophilic nature — better wetting in a moist oral environment; high stiffness in set state

Answer

Polyethers are hydrophilic, tolerating moisture better during setting than addition silicones (which are hydrophobic without special surfactants), giving better adaptation to wet gingival sulcus tissue.

Question 4

What is the purpose of a cavity varnish in amalgam restorations?

Accepted Answer

Seal dentinal tubules to reduce microleakage and post-operative sensitivity before placement of amalgam (mostly historic — now replaced by bonded amalgam or liners)

Answer

Cavity varnish was traditionally applied to seal dentinal tubules, reducing early microleakage (before amalgam corrodes to seal margins) and post-operative sensitivity; its use has largely been superseded by adhesive systems.

Question 5

What is the difference between resilience and toughness in dental materials science?

Accepted Answer

Resilience is energy absorbed in elastic deformation (before permanent deformation); toughness is total energy to fracture (elastic + plastic)

Answer

Resilience is the area under the elastic portion of the stress-strain curve (energy returned on unloading); toughness is the total area under the entire stress-strain curve to fracture — including plastic deformation.

MJDF Part 1 Practice Test

MJDF Part 1 Practice Test

MJDF Dental Materials Science 4