NBDE Part 2- Operative Dentistry
Exam 2025 Questions and Answers
Composite resin restoration is NOT recommended for this (class/tooth) -
ANSWER✔✔-Class III
DL aspect of canines
amalgam/direct gold indicated
Composite will not maintain the MD dimension of the tooth
Amalgam is a poor/good thermal insulator - ANSWER✔✔-poor
What materials are used under most amalgam restorations to provide thermal
protection? - ANSWER✔✔-CaOH or ZOE base
Ideal depth of amalgam prep and dentin remaining for adequate pulpal insulation is
_____mm into dentin and _____mm remaining - ANSWER✔✔-0.5
2.0
,Amount of mercury remaining in a set amalgam restoration is related to -
ANSWER✔✔-how much of the mercury-rich matrix is left in the amalgam after
condensation
Mercury-rich matrix is removed by - ANSWER✔✔-condensing and carving amalgam
after placement
Amount of mercury remaining in amalgam after condensation directly affects -
ANSWER✔✔-- porosity
- compressive strength
- corrosive resistance
- surface finish of restoration
Longer the trituration time (mixing time of amalgam), smaller/greater the setting
expansion - ANSWER✔✔-smaller
Characteristics of properly triturated amalgam - ANSWER✔✔-Shiny, wet, smooth,
homogenous
T/F Overtriturated mix is preferable to undertriturated mix - ANSWER✔✔-T
Discolored, corroded, superficial layer frequently seen on the surface of amalgam is
most likely - ANSWER✔✔-sulfide
,what happens when amalgam is contaminated w/ saliva? - ANSWER✔✔-water in
saliva reacts with zinc to produce hydrogen gas --> resulting pressure from the
liberated gas produces SEVERE EXPANSION of the amalgam
(corrosion, post-op pain)
Compressive strength also decreases
For an amalgam restoration, the tensile strength is about ______ of its compressive
strength - ANSWER✔✔-1/5-1/8
That's why enamel is needed to support amalgam @ the margins of restorations
T/F. Amalgam is less abrasion-resistant than composite - ANSWER✔✔-F.
More abrasion-resistant
Minimum thickness of ___mm in axial areas to ____mm in areas of occlusal contact for
adequate compressive strength - ANSWER✔✔-0.75
1.5-2.00
If mercury content exceeds ___%, dramatic loss in strength results - ANSWER✔✔-55-
marginal breakdown, fracture, corrosion
Reaction between alloy particles and mercury - ANSWER✔✔-Silver-Tin alloy (gamma)
+ Mercury --> Silver-Tin alloy (gamma) + Silver- Mercury (gamma-one) + Tin-Mercury
(gamma-two)
, Gamma - ANSWER✔✔-Unreacted alloy
-strongest
-Corrodes the least
- Forms 30% of volume of set amalgam
Gamma-one - ANSWER✔✔-Matrix for unreacted alloy
- second strongest phase
- forms 60% of volume of set amalgam
Gamma-two - ANSWER✔✔-- Weakest and softest
- Most susceptible to corrosion
- Forms 10% of the voulme of the set amalgam
- Volume decreases with time due to corrosion
Low vs. High copper amalgam - ANSWER✔✔-- Low-copper amalgam contains
gamma-two phase
- Marginal defects (chipped margins) more often seen around low-copper amalgams
Smaller particle size (amalgam), lower/higher strength, lower/higher flow,
worse/better carvability - ANSWER✔✔-higher
lower
Exam 2025 Questions and Answers
Composite resin restoration is NOT recommended for this (class/tooth) -
ANSWER✔✔-Class III
DL aspect of canines
amalgam/direct gold indicated
Composite will not maintain the MD dimension of the tooth
Amalgam is a poor/good thermal insulator - ANSWER✔✔-poor
What materials are used under most amalgam restorations to provide thermal
protection? - ANSWER✔✔-CaOH or ZOE base
Ideal depth of amalgam prep and dentin remaining for adequate pulpal insulation is
_____mm into dentin and _____mm remaining - ANSWER✔✔-0.5
2.0
,Amount of mercury remaining in a set amalgam restoration is related to -
ANSWER✔✔-how much of the mercury-rich matrix is left in the amalgam after
condensation
Mercury-rich matrix is removed by - ANSWER✔✔-condensing and carving amalgam
after placement
Amount of mercury remaining in amalgam after condensation directly affects -
ANSWER✔✔-- porosity
- compressive strength
- corrosive resistance
- surface finish of restoration
Longer the trituration time (mixing time of amalgam), smaller/greater the setting
expansion - ANSWER✔✔-smaller
Characteristics of properly triturated amalgam - ANSWER✔✔-Shiny, wet, smooth,
homogenous
T/F Overtriturated mix is preferable to undertriturated mix - ANSWER✔✔-T
Discolored, corroded, superficial layer frequently seen on the surface of amalgam is
most likely - ANSWER✔✔-sulfide
,what happens when amalgam is contaminated w/ saliva? - ANSWER✔✔-water in
saliva reacts with zinc to produce hydrogen gas --> resulting pressure from the
liberated gas produces SEVERE EXPANSION of the amalgam
(corrosion, post-op pain)
Compressive strength also decreases
For an amalgam restoration, the tensile strength is about ______ of its compressive
strength - ANSWER✔✔-1/5-1/8
That's why enamel is needed to support amalgam @ the margins of restorations
T/F. Amalgam is less abrasion-resistant than composite - ANSWER✔✔-F.
More abrasion-resistant
Minimum thickness of ___mm in axial areas to ____mm in areas of occlusal contact for
adequate compressive strength - ANSWER✔✔-0.75
1.5-2.00
If mercury content exceeds ___%, dramatic loss in strength results - ANSWER✔✔-55-
marginal breakdown, fracture, corrosion
Reaction between alloy particles and mercury - ANSWER✔✔-Silver-Tin alloy (gamma)
+ Mercury --> Silver-Tin alloy (gamma) + Silver- Mercury (gamma-one) + Tin-Mercury
(gamma-two)
, Gamma - ANSWER✔✔-Unreacted alloy
-strongest
-Corrodes the least
- Forms 30% of volume of set amalgam
Gamma-one - ANSWER✔✔-Matrix for unreacted alloy
- second strongest phase
- forms 60% of volume of set amalgam
Gamma-two - ANSWER✔✔-- Weakest and softest
- Most susceptible to corrosion
- Forms 10% of the voulme of the set amalgam
- Volume decreases with time due to corrosion
Low vs. High copper amalgam - ANSWER✔✔-- Low-copper amalgam contains
gamma-two phase
- Marginal defects (chipped margins) more often seen around low-copper amalgams
Smaller particle size (amalgam), lower/higher strength, lower/higher flow,
worse/better carvability - ANSWER✔✔-higher
lower
