Biomaterials Final Flashcards by Nick Murray

3 Main Classes of Materials?

Metal
Ceramic
Polymer

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Metal Characteristics

Hard
Ductile (Tough/Bendable)
Strong

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Ceramics Characteristics

Hard
Brittle
Strong

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Polymers Characteristics

Soft
Ductile (Tough/Bendable)
Weak

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General Processing Characteristics of:
Metal-
Ceramics-
Polymers-

Metal- High temp
Ceramics- High temp
Polymer- low temp, direct processing

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Metallic Bond Properties?

Electrons are key, they have free mobility

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Metal alloys are _____ than pure metal

Stronger/Less ductile

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Ceramic Bond Characteristics?

Ionic and covalent bonds (stronger than metallic); non mobile ions

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Most dental ceramics are _____crystalline or ____crystalline

Semi

Poly

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The building block of Dental Porcelain (ceramics) is _______. It is process by _____ or _____

SiO4 tetrahedron

Sintering
Melting at High temps

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Polymer Bond Characteristics

Covalent bonds; mainly nonmetallic elements; derive strength/properties from entanglement (cooked spaghetti)

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Polymerization Process

Light activation of initiator
Initiation of monomer
Propagation of free-radical
Termination of free-radical

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Polymerization can be initiated by?

Light
Heat
Chemical mixing

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Physical mixtures of metals, ceramics, and/or polymers?

Composite

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By knowing the phases present in the structure of any material and interfacial interactions, it is possible to predict the overall properties fairly well.

Rule of Mixtures

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How do fillers affect properties?

Inc Filler vol. ->
Inc Filler Size
Inc Strength
Inc modulus
Inc Viscosity
Inc Surface roughness
Dec shrinkage

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Increased LCTE (Linear Coefficient Thermal Expansion) ->

Expands/Contracts more w/ temp change

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Metal (conductor) near the pulp -> _____ sensitivity, therefore metals need a ______

Composites have ____ thermal conductivity

High

Thermal insulator like base

Low

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Color has ____ dimensions, they are:

Hue- wavelength (color)
Value- intensity/brightness
Chroma- purity/density

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2 objects that appear the same color under one light source and different under another light source (different spectral characteristics)

Metamerism

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Linear vs Crosslinked chain:

A linear chain (monomethacrylates) grows from one end

A crosslinked chain (dimethacrylates) grows from both ends and makes branches

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Mercury Issues with amalgams:
Disposal-
Patient-
Operator-

Disposal- ends up in water systems
Patient- poor esthetics
Operator- brittle, sensitive

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The tendency of a solid material to deform permanently over time under low constant stresses

Creep

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Is amalgam ductile or brittle?

Ductile

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Corrosion of amalgam effects? Corrosion type?

Amalgam turns black over time Electrochemical corrosion (anode and cathode are the two phases)

Major reaction phase in low/high copper amalgam

Gamma 1

Does not form with high copper amalgam

Gamma 2

High copper alloys have ____ longevity and ____ creep values. Zn improves _______ and facilitates _____ particles

Greater Lower Corrosion resistance Lathe-cut

Setting Reaction: Initially there is _____ due to absorption of _____; then _____ from formation and growth of _____. Final absorption of mercury by remaining amalgam alloy particles causes _____

Contraction Hg Expansion Gamma phases Contraction

_____ is machined from a cast ingot and ____ is molten alloy blown through a nozzle. ______ resists forces of condensation less than _____ _____ is less uniform in size to optimize condensation.

Lathe-cut Spherical Spherical Lathe-cut Lathe cut

First step of setting reaction forms both _____ and _____. Second step shows disappearance of ___

Gamma 1 Gamma 2 Gamma 2

Relieves stresses in alloy particles and provides control of setting time. Eliminates compositional no uniformity in ingot before cutting.

Heat treatment of alloy

High Contact Angle vs Low Contact Angle

High contact angle is poor wetting and hydrophobic Low contact angle is good wetting and hydrophilic

_____ helps with polymerization of composites while _____ aids in adhering to a surface

Hydrophobicity Hydrophilicity

Electron transfer to allow for oxidation of a metal (corrosion)

Electrochemical (Galvanic) corrosion

Two phases (cathode and anode) that go through redox corrosion (amalgam)

Structure Selective Corrosion

Crack in the structure -> corrosion

Crevice Corrosion

Stress region (anode) and unstressed region (cathode)

Stress corrosion

Produces corrosion film that prevents further corrosion (implants)

Passive

What is immune to corrosion?

Noble metals (gold)

Ceramics degrade by:

Hydrolysis (covalent bonds broken down by water)

Polymers degrade by:

Hydrolysis (absorption of water leads to hydrolysis degradation)

Degradation of byproducts can be ____. ____ is a concern of amalgams and ______ is a concern of composites as it is estrogen like.

Toxic Mercury Bisphenol A

Stress limit where material ceases to return to original shape

Elastic Limit

Point where stress and strain are directly proportional (curve is straight line to this point)

Proportional Limit

Where material breaks (peak of curve)

Ultimate Strength

How stiff the material is (greater slope means greater stiffness)

Elastic Modulus

Curves that tend to be resistant to stress but cannot bear a lot of strain and will break (glass)

High elastic modulus

Will strain greatly under not much stress (red vine/polymer)

Low elastic modulus

Able to withstand stress and can strain to support more stress (tootsie roll/metal)

Medium elastic modulus

The energy absorbed before deformation occurs

Modulus (resilience)

The energy absorbed before failure/fracture

Toughness

____ and ____ can cause deformation of a material. ___ can change the setting time of a material.

Time Heat Heat

Ability of a cracked material to resist fracture

Fracture toughness

Multiple cycles of low stress

Fatigue

Cusps work as an entity when undergoing ____ forces (high stability), but when a cavity prep takes out the central groove the cups become separate entities subject to fracture.

Buccal to Lingual

Components of Composite Resins:

Organic- Resin -> processing and handling Inorganic- Filler -> modulus and wear resistance Coupling/Bonding agent

Trade-offs in composite properties:

Inorganic- resistant/strong but brittle and poor processing Polymer- poor resistance but tough and good processing

Allows for stronger one unit matrix to be formed

Cross linking (curing)

Greater crosslink density lead to:

Greater strength but more shrinkage

High filler loading results in ______. Smaller filler sizes lead to ____.

Higher modulus Better wear properties (for polishing) and better mechanical properties

Bind fillers to resin matrix

Coupling agents

____ results from density change of monomer to polymer. Leads clinically to ____ and ____.

Shrinkage Micro leaks Secondary caries

Glass-ionomer Cement components:

1. Polyacid 2. Basic glass 3. Water 4. Modifiers

Glass-Ionomer Cement is cured by ____. This forms ____ bonds which is different different from composites that use ____ bonds.

Acid-base rxn Salt bridge Covalent

The restorative mechanism of Glass-Ionomer Cement requires _____

Water

Upon setting of Glass-Ionomer Cement, ____ is released and will continue to be released over time.e

Fluoride

Adhesives are similar to Composites in their _____ chemistry, but are different because they are _____

Resin Unfilled/Lightly filled

Sealants differ from composites because they attach through ____ means rather than ____ means and they usually lack a ____.

Mechanical Chemical Filler

Area where oxygen interferes with radical polymerization at the surface leaving a thin layer often uncured

Oxygen inhibition layer

Polysulfied (good detail) impression material

Elastomer Impression Material

Alginate (not as accurate) impression material

Hydrocolloid impression material

Ideal Properties of Impression Materials:

- Low cost - Long shelf life - biocompatible - pleasant - stable - good handling properties

Pros and Cons of Water based alginates

Pros- economical, easy, fast, taste, hydrophilic Cons- dimensional instability, low tear resistance, limited details, single pour only, quick pour required

Undergoes shrinkage/expansion upon water loss/gain

Dimensional Stability

_____ are hydrophobic -> better stability for impressions But _______ can turn this material to hydrophilic

Polysiloxanes Surfactants

Is also hydrophobic but has better surface characteristics than Polysiloxanes. Also has good dimensional stability.

Polyethers

___ is used to make casts. It is cured by ____. When mixed with this curing agent, it is _____ and creates a ____ again (heat is released) Properties are dependent on ____ structure and ____

Gypsum Water Rehydrated Dehydrate Crystal Density

Dental _____ (not plaster) is used for models

Stone

Denture base is normally _____

VLC

Provisionals are normally ____ cured

Chemically

Mouth guards are _____ instead of thermoset (low softening point) and properties are controlled by a _____

Thermoplastic Copolymer

Used to bind restoration of appliances to tooth structure

Cements

Requirements for cements

Low viscosity with good mechanical properties

_____ ratio modifies the viscosity and handling properties of cement.

Powder-to-liquid

More filler (powder) leads to a more ____ and ____ cement. Less powder increases _____.

Viscosity Modulus Working and setting time

Cement type used for ortho, crowns, bridges, veneers. Similar chemistry to composite

Resin Cements

Two component cement type where you mix the liquid and powder

Glass Ionomer

Used to protect dentin from residual reactants that can diffuse out of the restoration/fluids that may leak in from the oral cavity; near pulp exposure

Liners

Used to provide thermal protection for pulp and mechanical support to resoration

Bases

Near or direct pulp exposure, use CALCIUM HYDROXIDE to initiate reparative dentin formation

Pulp Capping

Used as a sedative restoration (pain reduction)

Zinc Oxide and Eugenol (ZOE)

_____ should melt at low temps, be carve-able, burn off, and be dimensionally stable. They are lower molecular weight materials in between ____ and _____

Waxes Polymers Organic Liquids

Thermal Expansion coefficient relations between tooth, amalgam, and composite

Composite (Polymer) > Amalgam (Metal) > Tooth (and Ceramic)