Define biomaterials

Because biomaterials are not as durable as sound tooth tissue it is important to recognize the importance of:

1. Prevention of caries

2. Conservative treatments

3. Durability of treatments

1. Prevention of decay

2. Prevention of trauma

3. Realignment of teeth

4. Direct restorations

5. Indirect restorations

6. Prostheses

7. Implants

**Lab materials

Biocompatability

Interfacial properties

Chemical properties

Mechanical properties

Esthetics

Practicability

Objectives in measuring mechanical properties of materials:

1- Measure their fundamental properties

2- measure their properties under conditions attempting to simulate service conditions

Viscoelasticity

Fatigue

Impact

Stress-strain

Hardness (resistance to indentation

Resistance to abrasion

List the five types of stress:

Tension

Compression

Torsion

Flexur

Shear

Define strain:

Hooke's law

Constant; defines the rigidity of a material; larger slope = more rigid material, smaller slope = less rigid material

Maximum stress at which stress is proportional to strain

Define elastic limit:

Measure of ductility and maleability related to plastic strain; material with high percentage elongation = ductile; material with low percentage elongation = brittle

Brinell's (circle)

 Vickers (diamond)

Knoop (diamond)

A property having plastic and elastic behavior

Proteins

Polyisoprenes

Polysaccharides

Nylon

Silicon

Polysulfide

Types of acrylic

1- Acrylic fabric (not relevant to dental biomaterials)

2 - Acrylic resin (aka PMMA) used for dentures

3 - Acrylic acid - water soluble polymer for adhesive dental cements

1- Generation of free radicals (activation and initiation)

2 - Propagation of the reaction

3 - termination of the reaction

1 - Heat

2 - Radiation

3 - Chemical

1 - activator reacts with initiator to give free radicals

2 - Free radicals react with monomers to give larger free radical

3 - Propagation

4- termination

Four physical states of polymers

Elastomers (or rubbers)

Hard amorphous polymers (or glasses)

Hard paritally crystalline polymers (not relevant)

Polymeric fibers (not relevant)

(T_g)Polymer characteristic determining at what temperature a glass becomes brittle on cooling, or soft on heating

High T_g = rigid at mouth temperature

Low T_g = flexible at mouth temperature

- More elastic, less plastic deformation

- May have higher value of T_g

- Harder and more brittle

- More resistant to action of solvents

Define plasticizer

- Reduces forces between molecules

- Result is softened polymer

- Polymer may be more flexible (lower T_g)

Alternating

Random

Block

Graft

Define metal:

Material that exhibits both metallic and non-metallic behavior

Usually hard

Lustrous

Dense

Good conductor of heat

Good conductor of electricity

Opaque

Ductile and malleable

Casting

Cold working (forming a smaller diameter of wire)

Powder metallurgy

Electroforming

- Conductivity (movement of electrons)

- Opacity to light (electrons absorb electromagnetic energy)

- Easily forms alloys

- Solid metals can be considered sturcutrally as a regular arrangement of nucle at an equilibrium distance from each other

Material showing a long-range regular arrrangement of atoms (all metals are crystalline)

Body centered cube

Face centered cube

Hexagonal close packed

Point defects (substitutional and interstitial impurities; vacancies)

Line defects (the major reason for malleability and ductility of metals because dislocations propogate through structure; the more dislocations the more ductile a material)

Planar defects

Equiaxed coarse

Equiaxed fine

Fibrous grain

Effect of recrystallization on metal

1 - solid solution (one phase) - substitutional (random or ordered) or interstitial

2 - complete solid insolubility (two phases)

3 - partial solid insolubility (one or two phases)

4 - intermetallic compound formation

Au

Cu

Ag

Pt

Pd

1 - Solid solution formed during solidification and

2 - On cooling precipitation may occur

1 - chemical composition

2 - mechanical history

3 - thermal history

An alloy is harder than any of the individual metals from which it has been prepared

Hardness depends on:

number of different compounds 

relative amount of each component 

Cold working

Deformation of structure

Hinders movement of dislocations

Material less easy to deform

Harder 

Amalgam

Inlays, crowns, bridges

Bonding to porcelain

Wires, brackets, bands

Implants

Instruments 

pH levels

food particles

moisture

temperature

chemical effects 

1 - can be harmful to the body

2 - galvanic pain

3 - weakening of structures

4 - adverse effet on esthetics 

Tarnishing of bras

Surface discoloration by oxide formation 

Ti forms a protective oxide coating

Chromium (Cr) forms a protective oxide coating

Gold and amalgam

Plate and screw of same alloy (screw may be an anode because of irregular structure)

Differences because of electrolyte composition (probably won't happen in the mouth) 

1 - choose materials wisely  - must be noble (Au, Pt, Pd) or passive (Cr)

2 - Use materials wisely  by avoiding an electrolytic cell situation