ADEX Dental Biomaterials 4

Question 1

Which impression material is considered the most dimensionally accurate and is preferred for fixed prosthodontic impressions?

Accepted Answer

Polyvinyl siloxane (addition silicone)

Answer

Polyvinyl siloxane (addition silicone) is considered the gold standard for fixed prosthodontic impressions due to its exceptional dimensional accuracy and stability.

Question 2

In ceramics used for dental restorations, leucite crystals are added primarily to:

Accepted Answer

Increase fracture toughness and adjust thermal expansion coefficient

Answer

Leucite reinforcement increases the fracture toughness of porcelain and raises its coefficient of thermal expansion to match metal substructures in PFM restorations.

Question 3

When mixing alginate impression material, using cold water will:

Accepted Answer

Prolong the working and setting time

Answer

Cold water slows the chemical reaction in alginate, extending both working and setting times, which is useful when more manipulation time is needed.

Question 4

What is the primary cause of polymerization shrinkage in composite resins?

Accepted Answer

Van der Waals distances converting to shorter covalent bonds during crosslinking

Answer

During polymerization, monomers linked by van der Waals forces form shorter covalent bonds, reducing intermolecular distance and causing volumetric shrinkage.

Question 5

Agar (reversible hydrocolloid) impression material converts from gel to sol by:

Accepted Answer

Heating to approximately 100°C

Answer

Agar is a thermoreversible material that liquefies (sol) upon heating to ~100°C and gels upon cooling, allowing it to be reused multiple times.

ADEX - Dental Hygiene Exam Practice Test

ADEX - Dental Hygiene Exam Practice Test

ADEX Dental Biomaterials 4