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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
¢ Thermal expansion-
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
Heat flow-
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
METAMERISM
2 objects that appear the same color under one light source and different under another light sourse ¢ Different spectral characteristics
28
Wetting
How water interacts with surface. Wetting can be anticipated on the basis of the Hydrophobicity (water-hating) and hydrophilicity (water loving) of materials
29
SEALANTS
¢ Unfilled diluted resins ¢ Self or light cured ¢ Clear or opaque ¢ Radiopaque
30
HYDROPHILIC PRIMERS
Allow penetration into areas with water ¢ Usually mixed with a solvent (alcohol, acetone) ¢ Very low viscosity ¢ Allows for attachment to composite
31
Primary Bonding-
generally affected by chemical and electro chemical reactions
32
Secondary bonding
generally affected by processes such as adsorption (onto) and absorption (into)
33
corrosion.
¢ 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
Titanium-
Recently deemed noble metal
35
Active
lead to destruction (Gamma 2)
36
Passive
produce corrosion film that prevents further | corrosion (titanium implants)
37
Immune
noble metals (gold)
38
ELECTROCHEMICAL CORROSION (active)
*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
Chemical Dissolution
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
HOW ARE POLYMERS AFFECTED
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
BIOLOGIC PROPERTIES
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
¢ Single dimension
Compression — Tension — Shear
43
Combinations
Torsion (twisting) — Flexion (tensile) — Diametral Compression (tensile)
44
Resilience
before deformation
45
Toughness
Toughness-before failure or fracture occurs
46
MECHANICAL EVENTS ARE
time and temp dependent
47
MECHANICAL PROPERTIES VS. TIME
Degradation Affects Mechanical Properties ¢ Cracks or Non-Critical Defects Accumulate over Time ¢ Water is Absorbed into Materials
48
Creep (strain relaxation)
Deformation over time in response to low constant | stress
49
Stress relaxation
Deformation over time in response to low constant strain
50
FATIGUE -MULTIPLE CYCLES OF LOW STRESS
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
Jaw
Class III lever
52
¢ Abfractions
usually associated with heavy wear facets | ¢ Cyclic tension and compression of enamel rods lead to microfractures
53
Single cycle overload
“unexpectedlybitoncherrypit or bone” (rare)
54
Fatigue
cyclic loads well below breaking load — “Iwaseatingsomething soft” (more common) — Slowcrackpropagationover time

Op Dent 1 (17 decks)

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