Dental Materials NBDHE exam with complete solution 2024_2025
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Course
NBDHE
Institution
NBDHE
Adhesion
The chemical attraction between unlike molecules
Cohesion
The chemical attraction between like molecules
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Coefficient of thermal expansion
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Dental Materials NBDHE exam with
complete solution 2024/2025
Adhesion - ANSWER- The chemical attraction between unlike molecules
Cohesion - ANSWER- The chemical attraction between like molecules
Coefficient of thermal expansion - ANSWER- An index which indicated how one
material reacts to temperature extremes in relation to another
Compressive Strength - ANSWER- The force at which a material breaks under
pressure
Creep - ANSWER- Slow dimensional change caused by compression
Ductility - ANSWER- The ability to undergo change of form without breaking
Elasticity - ANSWER- Material's ability to recover its initial shape after undergoing
a force
Galvanism - ANSWER- An electrical current generated by dissimilar metals in an
acidic environment
Gelation - ANSWER- The process of gelling (solidification by cold)
Imbibition - ANSWER- Absorption of a solvent by a gel
Malleability - ANSWER- A material's capacity to be shaped by force or pressure
Microleakage (percolation) - ANSWER- Passage of oral fluids/bacteria into and
out of tooth structure due to marginal gap or failure of marginal (restorative) seal
Polymerization - ANSWER- The linking, branching, or cross-linking of smaller
molecules
, Proportional limit - ANSWER- The force at which a material cannot return to its
original shape
Syneresis - ANSWER- Contraction of a gel due to the loss of a solvent
Tensile strength - ANSWER- The force needed to stretch a material to the point of
fracture
Viscocity - ANSWER- Resistance to flow
Amalgam - ANSWER- By definition: an alloy of mercury
In dentistry: an alloy of mercury with silver, copper, tin, and zinc
Silver, a base metal, susceptible to corrosion
Copper added to minimize the corrosion (gamma II phase eliminated)
Amalgam desirable features - ANSWER- Durable
Similar compressive strength to enamel
Relatively inexpensive
Amalgam undesirable features - ANSWER- Unattractive
High thermal conductivity
Dimensionally unstable (creep)
Delayed expansion if contaminated by saliva
Requires tooth support
Fracturable by excessive occlusion
Susceptible to galvanism when new
Polishing Amalgam - ANSWER- Move from coarse to fine agents to remove
surface tarnish, stains, flash and roughness
Polishing can reduce rate of corrosion (less surface area)
Final polish in mouth is tin oxide
Use light touch with water and short bursts to avoid odontoblast damaging heat
Ways to avoid amalgam overhang formation - ANSWER- Using properly placed
band and wedge(s)
Detect overhang with explorer
Bonding agents; Dental Resins (BIS-GMA* or urethane dimethacrylate) -
ANSWER- Establishes micro mechanical retention with enamel and dentin by
adapting to relief areas created by conditioning with phosphoric acid
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