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Op Dent 1 > Materials Science 1 > Flashcards

Materials Science 1 Flashcards

1
Q

¢ Synthetic Biomaterials

A

— Composites

— Silicone Impression Materials

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2
Q

¢ Natural Biomaterials

A

— Alginates

— Hydrocolloids

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3
Q

¢ Tissue-engineered Biomaterials

A

— Stemcells
— Replacement tissues (Growing a Tooth from a Bud)
— Promising but still a generation away (>20yrs) ¢ 4 yrs to create a coronal portion of a tooth
¢ Cost effective and accelerated

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4
Q

Metals

A

Hard

— Ductile – Tough — Strong

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5
Q

Ceramics

A

Hard

— Brittle — Strong

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6
Q

Polymers

A

Soft

— Ductile - Tough — Weak

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7
Q

Processing characteristics

A

Metals and Ceramics Have High Processing Temperatures
¢ Polymers tend to Have Lower Processing Temperatures
¢ Polymers Tend to be used as Direct Processing Materials

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8
Q

METALLIC BONDS

A 
metallic elements have 1,2,3
electrons in their outer shell
¢ electrons are key to metallic bonds
¢ electrons are loosely bound to nucleus
¢ electrons have free mobility
—  thermal and electrical conductivity —  ductility-bend without breaking
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9
Q

Ductile

A

Ductile- atoms can slide - in essence a more uniform atom size.

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10
Q

Less uniform atom size

A

Stronger less ductile

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11
Q

CHARACTERISTICS OF CERAMIC BONDS

A

¢ ionic and covalent bonds associated with ceramics ¢ both are stronger than metallic bonds
¢ covalent >ionic
¢ ionic bonds - electron donor and electron acceptor ¢ covalent bonds-equally shared electrons
¢ non mobile ions

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12
Q

MICROSTRUCTURE OF CERAMICS

A

Mixture of metallic and non-metallic elements
¢ Most common ceramics in dentistry are 3 metallic oxides (SiO2,
Al2O3, K20)
¢ Crystalline (long range order) crystalline silicate-quartz or crystobilite
¢ Noncrystalline (short range order no long range) or amorphous silicate-glass
¢ Most dental ceramics are semicrystalline or polycrystalline
¢ SiO4 tetrahedron is the building block

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13
Q

MICROSTRUCTURE OF DENTAL PORCELAIN

A

¢ SiO4 tetrahedron is the building block
¢ primarily a glass with some crystalline residuals
— noncrystalline or amorphous silicate-glass
— crystalline silicates
¢ Quartz or crystobilite ¢ Leucite (not Lucite)
¢ Processed by Sintering or Melting at High Temperatures

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14
Q

CHARACTERISTIC POLYMER BONDS

A

¢ Covalent bonds
¢ High molecular weight
¢ Long molecules composed principally of nonmetallic elements (organic chemistry C,O,N,H)

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15
Q

Free Radicals Will Initiate

A

Methacrylate Polymerization

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16
Q

CQ (Yellow) absorbs visible light. Interacts with

A

DMAEMA To Generate Free Radicals.

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17
Q

RESIN MATRIX

A

Monomers ¢ Initiator

— hasten free radical reaction

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18
Q

¢ Direct Placement requirements

A

Flowable Material — Stable Material
— Trigger for Setting — Rapid Setting
— Room Temperature Setting Reaction

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19
Q

Metals – Indirect

A

High Processing Temperatures — Exception: Amalgam

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20
Q

Ceramics – Indirect

A

High Processing Temperatures — Exception: Cements

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21
Q

Polymers – Direct

A

Low Processing Temperatures — Exception: Indirect Composites

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22
Q

Dispersed phase

A

Glass fillers

23
Q

Matrix phase

A

Monomer resin

24
Q

¢ specific gravity

A

relative density = density of material/density of water

25
Q

¢ Thermal expansion-

A

most things expand when heated and contract when cooled
— Measure:LCTE-linear coefficient of thermal expansion- cm/cm/°C (ppm/°C)
— Ceramics (1-15 ppm/°C)

26
Q

Heat flow-

A

teeth are insulators due to high mineral content
— Measure: thermal conductivity-(rate of heat conduction)
— thermal diffusivity-(heat conduction/ unit time)
— Clinical consequence: Pulps can can withstand small temperature changes for short times (42°C for 60 sec) restricted circulation of pulp cannot dissipate heat and carry it away.
— Metals have high thermal conductivity so they need thermal insulator like base
— Composites have low thermal conductivity so they do not need base

27
Q

METAMERISM

A

2 objects that appear the same color under one light source and different under another light sourse
¢ Different spectral characteristics

28
Q

Wetting

A

How water interacts with surface. Wetting can be anticipated on the basis of the Hydrophobicity (water-hating) and hydrophilicity (water loving) of materials

29
Q

SEALANTS

A

¢ Unfilled diluted resins ¢ Self or light cured
¢ Clear or opaque
¢ Radiopaque

30
Q

HYDROPHILIC PRIMERS

A

Allow penetration into areas with water
¢ Usually mixed with a solvent (alcohol, acetone)
¢ Very low viscosity
¢ Allows for attachment to composite

31
Q

Primary Bonding-

A

generally affected by chemical and electro chemical reactions

32
Q

Secondary bonding

A

generally affected by processes such as adsorption (onto) and absorption (into)

33
Q

corrosion.

A

¢ The spontaneous destructive oxidation of metals is called corrosion.
¢ All metals corrode; in our normal atmosphere of 21% oxygen, all metals except gold, platinum, and palladium corrode spontaneously (noble metals).

34
Q

Titanium-

A

Recently deemed noble metal

35
Q

Active

A

lead to destruction (Gamma 2)

36
Q

Passive

A

produce corrosion film that prevents further

corrosion (titanium implants)

37
Q

Immune

A

noble metals (gold)

38
Q

ELECTROCHEMICAL CORROSION (active)

A

*An anode.-corroding metal
¢ *A cathode.-different metal (passive-supplied electrons to solution)
¢ *A conducting environment for ionic movement (electrolyte).
¢ *An electrical connection between the anode and cathode for the flow of electron current (metals)
¢ In amalgam anode and cathode are the two phases

39
Q

Chemical Dissolution

A

normally occurs through dissolution of oxides created by hydrogen bonding effects of water in local areas of high acidity.
¢ Examples
— Acids dissolve HA (caries, acid etch for enamel bonding)
— Acidulated fluoride treatments dissolve ceramic crowns may roughen surface or remove surface stain

40
Q

HOW ARE POLYMERS AFFECTED

A

Absorption of water into polymers (secondary
bonds)
— Dimensional changes
¢ Hydrolytic degradation and release of components (primary bonds)
— Water, enzymes (esterases), bacterial byproducts — Contributes to wear problem with composites

41
Q

BIOLOGIC PROPERTIES

A

No Adverse Reactions
¢ Limits the Choice of Materials – Why are There no New
Materials?
¢ Toxicity
¢ Sensitivity
— Metal ion interaction of concern (Hg, Ni)
— Polymer breakdown products of interest and concern
— Sensitivity Rxns to monomers (latex)

Toxicity
— Hg is a concern
— Bisphenol A - byproduct in BisGMA-estrogen like – concern of cancer-particularly children- are plastic bottles dangerous?

42
Q

¢ Single dimension

A

Compression
— Tension
— Shear

43
Q

Combinations

A

Torsion (twisting)
— Flexion (tensile)
— Diametral Compression (tensile)

44
Q

Resilience

A

before deformation

45
Q

Toughness

A

Toughness-before failure or fracture occurs

46
Q

MECHANICAL EVENTS ARE

A

time and temp dependent

47
Q

MECHANICAL PROPERTIES VS. TIME

A

Degradation Affects Mechanical Properties
¢ Cracks or Non-Critical Defects Accumulate over
Time
¢ Water is Absorbed into Materials

48
Q

Creep (strain relaxation)

A

Deformation over time in response to low constant

stress

49
Q

Stress relaxation

A

Deformation over time in response to low constant strain

50
Q

FATIGUE -MULTIPLE CYCLES OF LOW STRESS

A

Normally plastic strain (deformation) below the elastic limit is negligible
Under many cycles small amounts of deformation accumulate until failure occur at low stresses

51
Q

Jaw

A

Class III lever

52
Q

¢ Abfractions

A

usually associated with heavy wear facets

¢ Cyclic tension and compression of enamel rods lead to microfractures

53
Q

Single cycle overload

A

“unexpectedlybitoncherrypit or bone” (rare)

54
Q

Fatigue

A

cyclic loads well below breaking load
— “Iwaseatingsomething soft” (more common)
— Slowcrackpropagationover time

Op Dent 1 (17 decks)

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