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
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)
3
Q
describe yield strength
A
the measure of a material’s ability to resist permanent deformation
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
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
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
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
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
9
Q
what is fracture toughness
A
10
Q
what are physical properties?
A
- observations
- dimensional resistance
11
Q
describe dimensional change
A
12
Q
describe dimensional stability
A
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)
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
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
16
Q
describe amalgamation
A
17
Q
describe trituration
A
to crush, grind, or pound into small particles, to pulverize and comminute thoroughly
18
Q
describe amalgam alloy vs dental amalgam
A
- amalgam alloy
- the combination of solid materials
- dental amalgam
- amalgam alloy mixed with Hg
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
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
21
Q
what is the balanced composition of amalgam?
A
- Ag3Sn(gamma)
- small amount of Cu
- occasionally Zn
- 10 to 20 year durability
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
23
Q
describe the composition of the Ag-Cu eutectic
A
72% Ag
28$ Cu
24
Q
what is low Cu?
A
a type of alloy
25
what are the different types of high Cu?
* admixed regular (different Cu amounts)
* lathe cut - low Cu
* spherical - high Cu
* admixed unicompositional
* lathe cute - same Cu
* spherical - same Cu
* uncompositional
* spherical
26
what is the elemental composition of alloy?
* 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)
27
why is Zn part of the composition of alloy?
* 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
what are the 5 metallic phases in alloy
* Ag3Sn (gamma)
* Cu3Sn (epsilon)
* Cu6Sn5 (eta prime)
* Ag4Sn (beta)
* Ag-Cu (eutectic)
29
T or F:
the amount of liquid Hg used to amalgamate the alloy particles is sufficient to react with the particles completely
false
it is not sufficient
30
what is the weakest phase of low-Cu amalgam?
Sn7-8Hg (gamma 2)
31
compare the lathe cut and/or admixed alloys with spherical alloys
* 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
most amalgams will achieve \_\_\_% strength within 1 hour
most amalgams will achieve \_\_\_% strength by hour 24
* 40-60%\
* 100%
33
what are the mechanical and physical properties of dental amalgam?
* mechanical
* compressive strength
* tensile strength
* elastic modulus
* creep
* physical
* dimensional change
* dimensional stability
* corrosion resistance
* tarnish resistance
34
compare the elastic modulus of amalgam and composite resin
* amalgam
* 40-60 GPa
* composite resin
* 5-20 GPa
35
how is amalgam creep measured?
measured by the shortening of the specimen after compressive forces have been applied
36
what does a creep of \>1% indicate?
indicates Sn7-8Hg is in the mix
37
what is the most successful bonding of amalgam?
4-META
38
describe dimensional stability of amalgam
* 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
describe high Cu corrosion
* 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
describe the corrosion resistance of the different alloy phases
from greatest to least resistance:
gamma 1
gamma
epsilon
eta prime
gamma 2
41
what is the process of placing an amalgam alloy?
1. dispensing and mixing
2. placing
3. condensing
4. carving
5. polishing
42
what is Coombs type IV hypersensitivity?
* contact dermatitis
* most likely physiologic side effect to dental amalgam
* experienced by \<1% of the treated population
43
what is lichenoid reaction?
* 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
describe mercury safety
* vapor toxicity
* blood level toxicity
45
describe the 3 forms of mercury
* 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
describe noble metals vs. base metals
⦿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
describe the 4 types of noble casting alloys
▪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
describe high noble casting alloys
⦿High Noble - ≥ 60% Noble & ≥ 40% Au
Au-Ag-Pt
Au-Cu-Ag-Pd-I
Au-Cu-Ag-Pd-II
49
describe noble casting alloys
⦿Noble - ≥ 25% Noble
Au-Cu-Ag-Pd-III
Au-Ag-Pd-In
Pd-Cu-Ga
Ag-Pd
50
what are the 5 noble ceramo-metal casting alloys?
aka porcelain-fused-to-metal
* Au-Pt-Pd
* Au-Pd
* Au-Pd-Ag
* Pd-Ag
* Pd-Cu
51
what are the affects of minor elements in metal-ceramic alloys?
* 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
what are some common uses for base metal alloys in dentistry?
⦿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
what are some biocompatability/toxicity concerns of base metal alloys?
* 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
compare base metal alloys with noble metal alloys
* 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
compare density differences between gold alloys and base metal alloys
* base metal alloys have half the density of gold alloys
* advantage for large maxillary appliances
* disadvantage is that it is difficult to cast
56
describe corrosion of base metal alloys
* 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
describe mechanical properties of base metal alloys
* 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
what is pre-oxidation?
* 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
what is rutile?
* a black or reddish-brown mineral consisting of titanium dioxide, typically occurring as needle-like crystals
60
describe titanium
* 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
describe commercially pure titanium
⦿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
describe titanium allotropism
⦿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
describe titanium use in dentistry
* 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
what are some complications with titanium crowns, FPD, and RPD?
⦿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
what are wrought wires?
* 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
describe wrought forms
⦿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.
