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NBDE Part II > Dental Materials > Flashcards

Dental Materials Flashcards

1
Q

Cost comparison

A

polyether > PVS > condensation silicone > poly sulfide > reversible hydrocolloid > irreversible hydrocolloid (alginate)

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2
Q

Dimensional Stability comparison

A

PVS (1 week) > polyether (few hrs) > poly sulfides (1 hour) > condensation silicone > hydrocolloids

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3
Q

Wettability comparison

A

hydrocolloids > poly ether > PVS > poly sulfide > Hydrophobic PVS > condensation silicone

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4
Q

Stiffness comparison

A

Polyether > PVS > condensation silicone > polysulfide > hydocolloid

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5
Q

Tear strength comparison

A

polysulfide > PVS > poly ether > condensation silicone > hydrocolloid

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6
Q

castability comparison

A

Hydrocolloids > hydrophilic PVS > poly ether > polysulfide > hydrophobic PVS > condensation silicone

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7
Q

working time comparison

A

Reversible hydrocolloid > polysulfide > PVS > condensation silicone > polyether = Irreversible hydrocolloid

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8
Q

setting time comparison

A

Poly sulfide (8-12 min) > condensation silicone (6-8) > PVS (3-7) > rev. hydrocolloid (5) > polyether > Irrversible hydrocolloid (3.5)

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9
Q

Cement Luting Agents

A
  • provide a non-permeable marginal seal
  • Do not add to retention of crown, only increase frictional resistance.
  • Add cement to both tooth and crown

Types:

  1. ZnPhosphate
  2. ZnPolycarboxylate
  3. GI
  4. Resin modified GI
  5. Resin
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10
Q

Define the process in processing alloys:

  1. Heat treatment
  2. Quenching
  3. Annealing
  4. Tempering
  5. Fritting
  6. Degassing
  7. Pickling
A

Processing Alloys

Heat treatment = controlled heating and cooling to relieve internal stress to improve physical properties (Ex: Quench, anneal, tempering)

Quenching = rapid cooling post high temperature that is meant to maintain the mechanical properties with the crystalline structure, while softening the alloy for finishing. The casting is also more easily cleaned while maintaining its malleability and ductility. Ex: Type III Gold should be quenched within 30-40 sec of fabrication

Annealing = controlled heat and slow cool of the metal to manipulate, and make the metal tougher and less brittle (increase ductility and strength)

Tempering = hardening something by heat treatment

NOTE: Heat treating is annealing + hardening + tempering

Fritting = manufacturing low/medium fusing porcelains where the porcelain is grounded into fine powder so that it can be added over other metals to make a certain color.

Degassing = heat treatment = necessary for all gold-porcelain systems = heating a porcelain to 980 C to burn off any remaining impurities prior to adding porcelain

Pickling = An acidic solution which removes surface oxides from cast prior to polish

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11
Q

Coefficient of Thermal Expansion

A
  • Tendency of a material to change shape during temperature change (eat or drink hot)
  • When the difference in coefficient is high between a tooth and the restorative material, a break in the margins is high. This will risk percolation = cyclic ingress and egress of fluid at the margin, thus increasing recurrent marginal decay.
  • Thus, the BEST restorative material will always be AMALGAM or direct GOLD, even on a Class III-DL on a canine
Tooth	        11.4
Direct Gold	14.4
Amalgam	22-28
Composite	28-35
Unfilled resin	81-92
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12
Q

Adhesion

A

van der walls and chemisorption

Smaller the angle, the greater the gettability, the higher the adhesion potential

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13
Q

Toughness

A
  • Difficult to break

- Affected by yield strength, elongation percent and modulus of elasticity

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14
Q

Brittle

A

amalgam

  • opposite of toughness
  • fracture near its proportional limit
  • High compressive strength but low tensile strength. This is why amalgam must have a butt margin, and no bevel.
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15
Q

Strain

A

is the actual shape or deformation that accompanies stress
• Elastic = before permanent deformation occurs
• Plastic

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16
Q

Creep

A
  • Strain relaxation
  • Deformations over time in response to a constant stress
  • Susceptible to creep: weak materials or close to their melting point
  • Higher the creep, the greater risk of marginal discrepancy
  • Change the Creep in Amalgams:
    o High copper (low Mercury) = decrease creep
    o Undertitrate AND over-titrate = increase creep
    o Delay in time between condensation and titration = increase creep
    o Decrease condensation force = increase creep (since it increases final [Hg])
    o Note: Marginal leakage decrease over time where corrosion products (tin oxide, tin sulfide) seal gaps
17
Q

Modulus of elasticity

A
  • measure of the stiffness or rigidity of a material
  • Ratio of stress to strain below the elastic limit
  • The higher the modulus of elasticity, the more rigid and the less strain exhibited for a given stress
18
Q

Elastic Limit

A

Elastic Deformation takes place prior to plastic deformation. The difference between the two is called elastic limit.

  • The greatest stress a material can take and still be able to return to its original form.
  • If a material (i.e. dental wire) does not return to its original form after bending, its said to pass its elastic limit
19
Q

yield strength

A
  • Strength measured at the stress at which a small amount of plastic strain occurs
  • the stress slightly higher than the proportional limit.
20
Q

Resilience

A
  • Energy a material can absorb before the onset of deformation.
21
Q

Ductile

A
  • Ability to easily shape a metal to a form (extensive plastic deformation prior to fracture during tension)
  • % elongation = amount an object stretches (strain) = elastic deformation + plastic deformation
  • Depends on both plasticity and tensile strength
22
Q

Malleable

A
  • Ability to compress a metal/hammer it

- Depends on plasticity

23
Q

Gold vs Silver vs copper vs platinum. Most malleable and most ductile.

A

Most Ductile: Gold > Silver > Platinum

Most Malleable Gold > Silver > copper

24
Q

What is the anterior determinant of occlusion?

A

Overjet and overbite

25
Q

Resin polymerization shrinkage is limited by the ADA to what micrometers? But no detrimental effects are seen after what micrometers?

A

20….50

26
Q

Longest shelf life on impression materials

A

reversible hydrocolloids

NBDE Part II (13 decks)

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