DMD Dental Materials Science 1 — Questions and Answers
Question 1: Which time-dependent deformation property of dental amalgam refers to its slow permanent distortion under sustained compressive stress?
- Plasticity
- Creep (Correct answer)
- Brittleness
- Elasticity
Correct answer: Creep
Creep is the time-dependent permanent deformation of amalgam under sustained load, contributing to marginal deterioration over time.
Question 2: Which impression material sets through an irreversible chemical reaction and cannot be reconverted to its original state for reuse?
- Agar hydrocolloid
- Alginate (Correct answer)
- Polyvinyl siloxane
- Zinc oxide eugenol paste
Correct answer: Alginate
Alginate is an irreversible hydrocolloid — once it gels through an irreversible chemical reaction, it cannot be returned to its sol state.
Question 3: The primary setting reaction of zinc phosphate cement involves which chemical process?
- Free-radical polymerization
- Acid-base neutralization (Correct answer)
- Condensation polymerization
- Oxidation-reduction
Correct answer: Acid-base neutralization
Zinc phosphate cement sets by an acid-base neutralization reaction between zinc oxide powder and phosphoric acid liquid, forming zinc phosphate crystals.
Question 4: The silane coupling agent incorporated in composite resins primarily functions to:
- Initiate photoactivated polymerization
- Bond inorganic filler particles to the organic resin matrix (Correct answer)
- Provide radiopacity for radiographic detection
- Reduce the coefficient of thermal expansion
Correct answer: Bond inorganic filler particles to the organic resin matrix
Silane acts as a bifunctional molecule, bonding the inorganic filler particles to the organic resin matrix and improving the mechanical properties of the composite.
Question 5: Which property of a dental material specifically describes its resistance to permanent surface indentation?
- Hardness (Correct answer)
- Ductility
- Malleability
- Toughness
Correct answer: Hardness
Hardness is defined as resistance to permanent deformation or indentation of the surface, commonly tested by Vickers, Knoop, or Brinell methods.
Question 6: Which dental ceramic exhibits the highest fracture toughness among ceramic restorative materials due to a transformation toughening mechanism?
- Feldspathic porcelain
- Leucite-reinforced ceramic
- Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) (Correct answer)
- Lithium disilicate glass-ceramic
Correct answer: Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP)
Y-TZP zirconia has the highest fracture toughness because stress at a crack tip triggers a tetragonal-to-monoclinic phase transformation that impedes crack propagation.
Question 7: During light-cured composite polymerization, the material shrinks primarily in which direction?
- Toward the light source (Correct answer)
- Away from the light source
- Uniformly in all directions
- Only at the external surface
Correct answer: Toward the light source
Composite resins shrink toward the light source (the bonded surface) during polymerization as the resin chains contract toward the initiation point.
DMD Dental Materials Science 1
Which time-dependent deformation property of dental amalgam refers to its slow permanent distortion under sustained compressive stress?