ADAT Dental Materials & Biomechanics 2

Question 1

What is the significance of the critical stress intensity factor (KIC) in dental ceramics?

Accepted Answer

It quantifies the material's resistance to crack propagation

Answer

KIC (fracture toughness) quantifies a ceramic's resistance to crack propagation; higher KIC means the material can tolerate larger flaws before catastrophic fracture.

Question 2

Which cement is most appropriate for luting a porcelain-fused-to-metal (PFM) crown on a vital tooth with adequate retention form?

Accepted Answer

Resin-modified glass ionomer cement (RMGIC)

Answer

RMGIC combines the fluoride release of GIC with improved retention and reduced pulpal irritation, making it ideal for PFM crowns on vital teeth with good preparation.

Question 3

What is the ideal water-to-powder ratio for dental stone (Type III gypsum) compared to plaster (Type II)?

Accepted Answer

Stone uses less water than plaster, producing a denser, stronger product

Answer

Dental stone requires approximately 0.28–0.30 mL/g water versus 0.45–0.50 mL/g for plaster, resulting in a denser, harder material with lower porosity.

Question 4

Which property of wax makes it suitable for occlusal registration but problematic if not handled correctly?

Accepted Answer

Thermal contraction during cooling can cause dimensional inaccuracy

Answer

Wax contracts significantly during cooling from mouth temperature, causing distortion of bite registrations if not supported or poured immediately.

Question 5

Which type of indirect restoration is most appropriate for a large MOD cavity in a mandibular molar with a cracked marginal ridge?

Accepted Answer

Indirect composite or ceramic onlay

Answer

An onlay is the most conservative option that provides cusp coverage to protect cracked marginal ridges without unnecessary removal of sound tooth structure.

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ADAT Dental Materials & Biomechanics 2