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Dental Materials Supplemental Cards > Metals > Flashcards

Metals Flashcards

1
Q

what are the 7 main mechanical properties?

A
  • elastic modulus
  • strength
    • yield
    • flexural
    • compressive
    • tensile
  • creep
  • ductility
  • malleability
  • hardness
  • fracture toughness
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2
Q

describe elastic modulus

A
  • measure of rigidity
  • a measure of a material’s ability to resist elastic deformation
  • the higher modulus, the stiffer the material (meaning it is less elastic)
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3
Q

describe yield strength

A

the measure of a material’s ability to resist permanent deformation

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4
Q

describe flexural strength

A
  • aka modulus of rupture
  • a material’s ability to resist fracture when a bending force is applied
  • measures compressive and tensile strength
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5
Q

describe compressive strength and tensile strength

A

the measure of a material’s ability to resist being crushed or broken with the application of a pushing force

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6
Q

describe creep

A
  • a measure of the amount of plastic deformation of a material subjected to a compressive force over a given period of time
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7
Q

what is the elongation percent

A
  • the measurement of a material’s ability to be stretched up to its breaking bpoint
  • the formula: final length - initial length x100
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8
Q

describe hardness

A

the measure of a solid material’s ability to resist plastic deformation on its surface when a compressive force is applied

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9
Q

what is fracture toughness

A
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10
Q

what are physical properties?

A
  • observations
  • dimensional resistance
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11
Q

describe dimensional change

A
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12
Q

describe dimensional stability

A
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13
Q

describe corrosion

A
  • the progressive destruction of a metal by a chemical or electrochemical reaction
  • galvanism is a corrosive process that occurs when an electrical current is generated between dissimilar metals in a solution of electrolytes (such as the mouth)
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14
Q

describe tarnish

A
  • a thin layer of corrosion that can form on the surface of some metals
  • usually the result of an oxidation reaction with the metal
  • a tarnish layer can serve as a protection to the underlying metal
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15
Q

describe amalgam

A
  • alloy of Hg and one or more other metals
  • produced by mixing liquid Hg with solid particles of an alloy containing predominantly Ag, Sn, and Cu
  • Zn, In, Pd and Pt may also be present in small amounts
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16
Q

describe amalgamation

A
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17
Q

describe trituration

A

to crush, grind, or pound into small particles, to pulverize and comminute thoroughly

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18
Q

describe amalgam alloy vs dental amalgam

A
  • amalgam alloy
    • the combination of solid materials
  • dental amalgam
    • amalgam alloy mixed with Hg
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19
Q

what are the advantages of amalgam?

A
  • relatively easy to place
  • not overly technique sensitive
  • relatively long service life
  • inexpensive, relative to other materials
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20
Q

what are the disadvantages of amalgam?

A
  • color
  • patient concerns over reported toxicity
  • concern about impact of amalgam disposal on wastewater and environment
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21
Q

what is the balanced composition of amalgam?

A
  • Ag3Sn(gamma)
  • small amount of Cu
  • occasionally Zn
  • 10 to 20 year durability
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22
Q

what is eutectic?

A
  • a mixture of substances in fixed proportions, that melts and solidifies at a single temperature that is lower than the melting points of the separate constituents or of any other mixture of them
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23
Q

describe the composition of the Ag-Cu eutectic

A

72% Ag

28$ Cu

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24
Q

what is low Cu?

A

a type of alloy

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25
Q

what are the different types of high Cu?

A
  • admixed regular (different Cu amounts)
    • lathe cut - low Cu
    • spherical - high Cu
  • admixed unicompositional
    • lathe cute - same Cu
    • spherical - same Cu
  • uncompositional
    • spherical
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26
Q

what is the elemental composition of alloy?

A
  • Ag - 40-60% (increases strength)
  • Sn - 26-30% (regulates expansion and setting)
  • Cu - 13-30% (increases strength and hardness, decreases corrosion and creep)
  • Zn - <0.01% (prevents oxidation)
  • In - 0-5% (increases strength, decreases creep)
  • Pd - 0-1% (decrease tarnish and corrosion)
  • Pt - 0-1% (increases tensile and compressive strength)
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27
Q

why is Zn part of the composition of alloy?

A
  • included to help produce clean, sound ingots from which the lathe cut particles are made
  • Zn can be bad if moisture contamination occurs during amalgam placement, because Zn will cause delayed expansion of the set amalgam
28
Q

what are the 5 metallic phases in alloy

A
  • Ag3Sn (gamma)
  • Cu3Sn (epsilon)
  • Cu6Sn5 (eta prime)
  • Ag4Sn (beta)
  • Ag-Cu (eutectic)
29
Q

T or F:

the amount of liquid Hg used to amalgamate the alloy particles is sufficient to react with the particles completely

A

false

it is not sufficient

30
Q

what is the weakest phase of low-Cu amalgam?

A

Sn7-8Hg (gamma 2)

31
Q

compare the lathe cut and/or admixed alloys with spherical alloys

A
  • lathe cut and/or admixed alloys
    • more condensable
    • easier to establish proximal contacts
    • less post operative sensitivity
  • spherical alloys
    • better early strength
    • smoother surface
    • more easily adapted around retentive pins
    • requires less Hg
32
Q

most amalgams will achieve ___% strength within 1 hour

most amalgams will achieve ___% strength by hour 24

A
  • 40-60%\
  • 100%
33
Q

what are the mechanical and physical properties of dental amalgam?

A
  • mechanical
    • compressive strength
    • tensile strength
    • elastic modulus
    • creep
  • physical
    • dimensional change
    • dimensional stability
    • corrosion resistance
    • tarnish resistance
34
Q

compare the elastic modulus of amalgam and composite resin

A
  • amalgam
    • 40-60 GPa
  • composite resin
    • 5-20 GPa
35
Q

how is amalgam creep measured?

A

measured by the shortening of the specimen after compressive forces have been applied

36
Q

what does a creep of >1% indicate?

A

indicates Sn7-8Hg is in the mix

37
Q

what is the most successful bonding of amalgam?

A

4-META

38
Q

describe dimensional stability of amalgam

A
  • delayed expansion in Zn containing alloys resulting from moisture contamination
  • contamination can occurs anytime during mixing or condensing
  • expansion begins between 3-5 days after placement and may continue for months
  • can cause pain
39
Q

describe high Cu corrosion

A
  • corrosion can occur on and within the amalgam through the interaction of dissimilar metals
  • corrosion can lead to increased porosity, reduced marginal integrity, loss of strength, and the release of metallic products
40
Q

describe the corrosion resistance of the different alloy phases

A

from greatest to least resistance:

gamma 1

gamma

epsilon

eta prime

gamma 2

41
Q

what is the process of placing an amalgam alloy?

A
  1. dispensing and mixing
  2. placing
  3. condensing
  4. carving
  5. polishing
42
Q

what is Coombs type IV hypersensitivity?

A
  • contact dermatitis
  • most likely physiologic side effect to dental amalgam
  • experienced by <1% of the treated population
43
Q

what is lichenoid reaction?

A
  • allergic reaction to amalgam
  • Most common site: buccal mucosa immediately opposite a buccal amalgam
  • May occur on ventral surface of tongue adjacent to lingual amalgam
44
Q

describe mercury safety

A
  • vapor toxicity
  • blood level toxicity
45
Q

describe the 3 forms of mercury

A
  • elemental Hg
    • released into air with fossil fuels combustion
  • inorganic Hg
    • found in the environment in combination with sulfur and oxygen
  • organic Hg
    • methylmercury found in soil and water thimerosal, phenylmercuric acetate, and other organic mercury compounds are synthesized and used as preservatives
46
Q

describe noble metals vs. base metals

A

⦿Noble Metals

  1. Metals that retain their surface luster in dry air
  2. Metals that resist oxidation, tarnish and corrosion

⦿Base Metals

  1. Metals that do not retain their surface luster in dry air
  2. Metals that oxidize, tarnish and corrode more easily
47
Q

describe the 4 types of noble casting alloys

A

▪Type I: Soft; Simple Inlays

▪Type II: Medium; Complex Inlays, Onlays, Single Unit Crowns

▪Type III: Hard; Crowns and Fixed Dental Prostheses

▪Type IV: Extra hard; Partial Denture Frameworks

48
Q

describe high noble casting alloys

A

⦿High Noble - ≥ 60% Noble & ≥ 40% Au

Au-Ag-Pt

Au-Cu-Ag-Pd-I

Au-Cu-Ag-Pd-II

49
Q

describe noble casting alloys

A

⦿Noble - ≥ 25% Noble

Au-Cu-Ag-Pd-III

Au-Ag-Pd-In

Pd-Cu-Ga

Ag-Pd

50
Q

what are the 5 noble ceramo-metal casting alloys?

A

aka porcelain-fused-to-metal

  • Au-Pt-Pd
  • Au-Pd
  • Au-Pd-Ag
  • Pd-Ag
  • Pd-Cu
51
Q

what are the affects of minor elements in metal-ceramic alloys?

A
  • Indium, Tin, Gallium, Cobalt
    • enhance metal-ceramic bond, increase strength of alloy, lower the fusion temperature
  • ​Iron
    • strengthens alloy
  • Copper and Cobalt
    • produce dark oxide
  • Silver
    • can cause “greening”
52
Q

what are some common uses for base metal alloys in dentistry?

A

⦿Removable Partial Denture (RPD) Frameworks

⦿Copings for Ceramo-Metal (PFM) Restorations & Fixed Partial Denture (FPD) Frameworks

⦿Endodontic Instruments

⦿Orthodontic Wires & Brackets

⦿Pre-Formed Crowns

⦿Implants [Titanium]

53
Q

what are some biocompatability/toxicity concerns of base metal alloys?

A
  • Be, in both vapor and particulate form, is associated with contact dermatitis, chronic lung disease, lung carcinoma & osteosarcoma
  • Ni is an allergen.
    • Sensitivity to Ni is 5 to 10 times higher for females than males
    • 5% to 8% of females show sensitivity to Ni
54
Q

compare base metal alloys with noble metal alloys

A
  • Have higher hardness values than noble metal alloys
  • Have a higher elastic modulus than noble metal alloys
  • Are more difficult to cast and solder than noble metal alloys
  • Are more technique sensitive than noble metal alloys
  • Undergo more solidification shrinkage than noble metal alloys
55
Q

compare density differences between gold alloys and base metal alloys

A
  • base metal alloys have half the density of gold alloys
  • advantage for large maxillary appliances
  • disadvantage is that it is difficult to cast
56
Q

describe corrosion of base metal alloys

A
  • Dependent upon:
    • Electrolytic Media (the solution or salivary composition)
    • Alloy Composition
    • Alloy Microstructure
    • Surface State of the Alloy (usually a different composition than the bulk of the alloy)
  • Corrosion Coupled with Wear:
    • 3X Ni ions released!
57
Q

describe mechanical properties of base metal alloys

A
  • Elastic Modulus
    • Elastic modulus of base metal alloys is twice that of Au alloys
    • Greater rigidity allows the fabrication of restorations with reduced dimensions
  • Hardness
    • Base metals are harder than Au alloys
    • Polishing techniques are more complicated
  • ​Yield Strength
    • Minimum of 415 MPa needed to maintain RPD clasp integrity
  • Tensile Strength
    • Base metal alloys are all greater than 800 MPa
  • Percent Elongation
    • Wide variability among base metal alloys:
    • Too high: The RPD clasp cannot maintain it’s shape
    • Too low: The RPD clasp is too brittle and breaks
58
Q

what is pre-oxidation?

A
  • Relieves internal stresses
  • Forms an outside layer of metal oxides with which the porcelain forms a chemical bond
  • This process is unique and specific to each of the metal alloys
59
Q

what is rutile?

A
  • a black or reddish-brown mineral consisting of titanium dioxide, typically occurring as needle-like crystals
60
Q

describe titanium

A
  • Ninth most abundant element in the earth’s crust
  • Fourth most abundant structural metal
  • Commercial production began in 1950s
  • Worldwide titanium production is now over 25,000 tons, annually
  • High strength/density ratio
  • Excellent corrosion resistance
  • passivates by forming a very stable protective layer
61
Q

describe commercially pure titanium

A

⦿CP Grade I

⦿CP Grade II

⦿CP Grade III

⦿CP Grade IV

⦿Each grade varies according to oxygen and iron content

⦿These slight concentration differences have a profound effect on the physical and mechanical properties of the titanium

62
Q

describe titanium allotropism

A

⦿α Phase – Hexagonal close-packed (HCP) crystal lattice

⦿β Phase – Forms at temperatures above 883˚ C, body-centered cubic (BCC) form

⦿Alloying Ti with other metals preferentially stabilizes either the α or the β phase to influence the properties of the Ti alloy

63
Q

describe titanium use in dentistry

A
  • Implants
    • Machined
  • Crowns
    • Computer Aided Machining (CAM)
    • Electrical Discharge Machining or Spark Erosion
    • Cast
  • FPD Frameworks
    • Computer Aided Machining (CAM)
    • Electrical Discharge Machining or Spark Erosion
    • Cast
  • RPD Frameworks
    • Computer Aided Machining (CAM)
    • Electrical Discharge Machining or Spark Erosion
    • Cast
64
Q

what are some complications with titanium crowns, FPD, and RPD?

A

⦿Abrasive machining (CAM) of titanium is slow and inefficient

⦿Spark erosion technology is expensive and technique sensitive

⦿Currently, technologies to cast, machine, weld &/or veneer titanium with porcelain are very technique sensitive and expensive

65
Q

what are wrought wires?

A
  • beaten out or shaped by hammering
  • “cold-working”
  • Wrought wires can be soldered to a existing RPD framework.
  • Wrought wires can be cast to a new RPD framework
66
Q

describe wrought forms

A

⦿Wrought forms have a fibrous microstructure that results from the cold work applied during the operations that shapes the metal.

⦿This cold work increases both tensile strength and hardness.

⦿Prolonged heating of wrought forms can cause them to recrystallize and develop a grain structure similar to their cast form.

⦿Recrystallization adversely affects the mechanical properties.

⦿Severe recrystallization can cause wrought forms to become brittle.

⦿Heating operations must be minimized when working with wrought forms.

Dental Materials Supplemental Cards (6 decks)

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