Dental Materials Science Flashcards

Which ADA/ISO type of gypsum product has the highest compressive strength?

Answer: Type V — high-strength, high-expansion stone

Type V gypsum (high-strength, high-expansion die stone) has the highest compressive strength of all gypsum types, exceeding 35 MPa, making it suitable for precision die work.

Which monomer is the primary liquid component in heat-cured PMMA denture base resins?

Answer: Methyl methacrylate (MMA)

Methyl methacrylate (MMA) is the primary liquid monomer in conventional PMMA denture base resins; when polymerised it forms polymethyl methacrylate (PMMA).

Which elastomeric impression material has the best dimensional stability after removal from the mouth?

Answer: Addition silicone (polyvinyl siloxane, PVS)

Addition silicone (PVS) has the best dimensional stability because its hydrosilylation setting reaction produces no volatile by-products, resulting in negligible post-set dimensional change.

The primary mechanism by which 4th-generation dentine bonding agents achieve adhesion is:

Answer: Micromechanical interlocking through hybrid layer formation in demineralised dentine

4th-generation bonding agents use a separate etch-prime-bond sequence to form a 'hybrid layer' — resin monomers infiltrate the acid-demineralised collagen network and polymerise, achieving micromechanical retention.

What stabilises the tetragonal crystal phase of zirconia in yttria-stabilised tetragonal zirconia polycrystal (Y-TZP) ceramics?

Answer: Yttrium oxide (yttria) doping

Yttrium oxide (yttria, Y2O3) is added in small amounts (3 mol%) to stabilise the tetragonal phase at room temperature, enabling transformation toughening when cracks propagate through the material.

Which component in ZOE-based root canal sealers is primarily responsible for periapical tissue cytotoxicity?

Answer: Eugenol

Eugenol is the cytotoxic component in ZOE-based sealers; it causes tissue irritation, inhibits pulp cell proliferation, and is toxic to periapical tissues when in direct contact.

What is the primary setting reaction of addition silicone (PVS) impression material?

Answer: Platinum-catalysed hydrosilylation of Si-H groups across vinyl groups

Addition silicones set via a platinum-catalysed hydrosilylation reaction in which Si-H groups add across vinyl (Si-CH=CH2) groups with no by-product released, giving excellent accuracy and dimensional stability.