Biomaterialse1

Front 1

1. A high gold casting alloy is selling for $930/oz. A non-noble casting alloy sells for $31/oz. The density of the gold alloy is 16 g/cm3, that of the non-noble alloy is 8 g/cm3. To cast the same crown in the gold alloy would cost how much compared to the non-noble alloy (considering alloy cost only – e.g., ignoring other material costs and labor costs)?

Back 1

930/31 = 30 (more expensive by weight) 2* 30 = 60

Front 2

2. When a plate of material is laid on this page, the words can still be discerned, but they are blurry and difficult to read. The material is said to be

Back 2

Translucent

Front 3

3. Thermal conductivities generally increase in the order

Back 3

Polymers, ceramics, metals

Front 4

4. Transient temperature changes are not only conducted through materials, but alter the temperatures of the materials themselves. This combined effect is measured by thermal diffusivity. Assuming density (ρ) stays constant, thermal diffusivity is highest when

Back 4

Thermal conductivity is the highest in combination with the heat capacity (specific heat) being the lowest

Front 5

5. Noble metals are generally those with very negative standard electrode potentials.
These metals are inherently resistant to corrosion. However, even very active metals can resist corrosion if they form a protective oxide film and are said to

Back 5

Passivate

Front 6

6. Which of the following is not a characteristic of this protective oxide layer?

Back 6

Dense ( completely covers surface), adherent, impermeable (oxygen cannot continue to pass through it) ARE characteristics

Front 7

7. Noble metals are by definition metals

Back 7

Whose oxides break down in air (spontaneously oxidize) to yield free metal.

Front 8

8. One of the passivating metals is unusual in that it can convey passivity to it alloys, even to alloys in which it is present in small (< 20%) concentrations. That metal is

Back 8

Chromium (making it very unique in this regard)

Front 9

9. Which of the following is most likely to represent the way a drop of a good adhesive would look when placed on an adherend?

Back 9

Lowest angle (refer to Wetting in the lecture)

Front 10

10. Wetting plays an important role in adhesion to smooth surfaces, and is important in adhesion involving micromechanical interlocking.

Back 10

True

Front 11

. The stress-strain curve below represents the tensile strength test of a dental resin. It may be discerned that the elastic limit of the resin is:

Back 11

Elastic limit where it is the end of the straight line-no permanent strain as long as you are in linear region

Front 12

Ultimate strength is

Back 12

the maximum stress that a material can withstand while being stretched or pulled before failing or breaking.
Highest point on a stress strain curve

Front 13

3. The strain at the elastic limit is (character in figure answer of question)

Back 13

X2

Front 14

Resilience is

Back 14

Area under the curve before the elastic limit

the energy a material can absorb without undergoing any permanent deformation (i.e., like a spring)

Front 15

The modulus of elasticity is

Back 15

Y2/X2 (from question one), or slope in linear portion of curve
Stress/Strain

Front 16

The elongation at fracture is

Back 16

The deformation resulting from the application of a tensile stress. The permanent elongation may be determined by subtracting the strain at the elastic limit from the strain at the stress in question.

Front 17

Yield Strength is

Back 17

intersection of the stress strain curve and a line drawn parallel to the linear portion and passing through the offset.

Front 18

The toughness is:

Back 18

The toughness is the energy per unit volume absorbed by the material up to the point of fracture. The toughness is the area under the entire stress strain curve including both elastic and plastic regions.

Front 19

A partial denture is removed from the mouth three times daily for cleaning. After two years, one of the clasp arms* fractures. You question the patient (a friend and reliable witness) about the nature of the failure. She tells you that the clasp arm fractured during removal and assures you that nothing unusual was done -- she had removed the denture as usual with no unusual motions or forces. Visual inspection reveals no evident mechanical damage, permanent deformation, wear or other localized defects anywhere on the partial denture, including at the site of fracture. You conclude that the partial denture alloy probably had insufficient

Back 19

(Result of fatigue) - resilience

Front 20

If a student attempts to get an orthodontic wire appliance "just right" by repeated bending (such that the wire stays bent when the force is released) and straightening of the wire at the same point until the wire fractures, he has induced a fatigue fracture in the wire.

Back 20

False, that’s a work hardening fracture.

Front 21

1.Which property most precisely defines metals and distinguishes them from other elements?

Back 21

Thermal coefficient of electrical resistivity

Front 22

The defect which most markedly influences mechanical properties of metals and alloys (and other crystalline materials) is

Back 22

Dislocation

Front 23

In binary metal alloys, homogeneous solid solutions will not form between metallic elements if:

Back 23

Difference in atomic size is too great.

[The solution must be crystalline and the crystal lattices must fit with one another]
• <15% Atomic radius difference,
• same valence,
• same crystal structure,
• no appreciable difference in electronegativity

Front 24

If two metals form an alloy system exhibiting total solid solubility, the entire phase diagram (disregarding gaseous phases) will contain:

Back 24

S, L and S+L phases

Three fields:
o Liquid, high temperatures
o Solid, low temperatures
o Intermediate temperatures with a mix of solid/liquid phases

Front 25

In the solid solution diagram at the right, what would the composition of the liquid phase be when an alloy of overall composition ??% Columbium (Cb)-??% Titanium (Ti) had cooled to ???? °C?

Back 25

Given where isotherm process is.

At 65% B and 35% A, at temperature T, the alloy composition is a two-phase solution with some solid and some liquid.

The solidus at temperature T occurs when the composition is 20% A and 80% B

The liquidus occurs at temperature T when the composition is 60% A and 40% B.

(graph for this one)

Front 26

In the same Cb - Ti alloy system, if the alloy were cooled very rapidly (quenched) from 2400 °C to room temperature one would expect the alloy to exist as

Back 26

A non-amorphous solid

Front 27

Two of the hardening mechanisms for metals and alloys depend on the fact that it is more difficult to move a dislocation through other dislocations than through “perfect” crystal lattice. Those two are

Back 27

Work hardening and Grain boundary hardening. Grain boundaries are a cluster of dislocations, so increase in grain border density (smaller grains).

Front 28

Two of the hardening mechanisms for metals and alloys depend on the presence of a finely divided second phase distributed throughout the grains (crystals) of the primary phase. From the list in question 7, those two are

Back 28

Dispersion hardening and Precipitation hardening

Front 29

Slow cooling is a softening mechanism for all metal alloys.

Back 29

False

Front 30

In the eutectic diagram below, the alloy having the overall composition indicated by the vertical line at the temperature indicated by the horizontal line would consist of:
(graph Q10L3)

Back 30

–60% A, 40% B at temperature T the composition would consist of two phases, L and alpha.

Front 31

role of light scattering in the appearance and color of an object

Back 31

The more light scatters, the less reflective a surface is. Another way to look at this is: the rougher the texture, the greater the scattering. This also leads to dull colors, or less vibrant colors, and less of a mirror-like image.

Front 32

How do reflectance and refraction influence and alter the transparency of an object?

Back 32

The more reflective and/or refractive a surface is, the less transparent it is. Note there’s a difference in reflection and refraction: reflection is light being bounced back. Refraction is light being bent as it passes through an object. Higher the density, the more refraction occurs. Both reflectance and refraction affect the transparency of an object.

Front 33

explain the concept of translucency and relate it to opacity, transparency and light scattering.

Back 33

Translucency is the level “in between” opaque and transparent. Most light gets through (is “transmitted”) through the material. Images are not passed through. Highly translucent means almost transparent, but the image looks fuzzy.

Front 34

• Know that when light illuminates an object, __________ of some wavelengths will occur upon reflection and/or transmission through the object.

Back 34

absorption (selective removal)
Also, the higher the energy of the light (meaning shorter wavelengths), the more it scatters. Dominant wavelength of light scattered back is violet and blue.

Front 35

Describe the relationship between absorption and perceived color. Those wavelengths not absorbed (i.e., not removed) are perceived as color.

Back 35

The wavelengths reflected or refracted (scattering is a special form of reflection) back is what our eyes pick up.

Front 36

• Know that color has______ dimensions and be able to describe the parameters of hue, value and chroma that define color space.

Back 36

3

Hue- what we call color, i.e- Red. In color theory, that’s the dominant wavelength.
Hue – Dominant Wavelength, not absorbed.
Value - Gray color. Lowest “Value” is black. (ex: Coal black)
Chroma - Intensity of the hue. Color Saturation, intensity or strength of the color. (Dominant hue of pink: red, scarlet has a the same dominant hue of pink). Chroma is like diluting the hue.
Also note: Hue-Chroma portion can be mixed to produce any color. Mixing any two will produce a third primary color.

Front 37

Hue

Back 37

What we call color, i.e- Red. In color theory, that’s the dominant wavelength.
Dominant Wavelength, not absorbed.

Front 38

Value

Back 38

Gray color. Lowest “Value” is black. (ex: Coal black)

Front 39

Chroma

Back 39

Intensity of the hue. Color Saturation, intensity or strength of the color. (Dominant hue of pink: red, scarlet has a the same dominant hue of pink). Chroma is like diluting the hue.
Hue-Chroma portion can be mixed to produce any color. Mixing any two will produce a third primary color.

Front 40

Concept and consequences of the additive (and subtractive) nature of color.

Back 40

Colors in transmission – additive color (looking through a tinted window and seeing a green chair, it seems like a darker green chair due to the dark tinted window in front of it, ‘adding’ color).
Colors in reflection – subtractive (i.e when we look at a green chair, red is being absorbed).

Front 41

Colors in transmission

Back 41

additive color (looking through a tinted window and seeing a green chair, it seems like a darker green chair due to the dark tinted window in front of it, ‘adding’ color).

Front 42

Colors in reflection

Back 42

subtractive (i.e when we look at a green chair, red is being absorbed).

Front 43

When mixing pigments, any change in______ will be accompanied by a decrease in value.

Back 43

Hue
(Look at image in power points)

Front 44

Daylight, incandescent, and fluorescent lamps are common sources of light in the______ or ________, and each of these has a different ______ _______.

Back 44

dental operatory or laboratory; spectral distribution.

Front 45

White light is has the same________ at all wavelengths. The light source is _______ intense throughout the visible spectrum.

Back 45

intensity; equally
Sidenote: Fluorescence is not reflected light, it is transmitted light.

Front 46

Metamerism

Back 46

Objects that appear to be color-matched under one type of light may appear different under another type.

Front 47

Phenomenon in which the color of an object under one type of light source appears to change when illuminated by a different light source.

Back 47

Metamerism

Front 48

Clinical correlation: If possible, color matching should be done under two or more different ______, one of which should be _____, and the laboratory shade-matching procedures should be performed under the same lighting conditions.

Back 48

light sources; daylight

Front 49

Role of the human eye in color perception

Back 49

Signals of color are sent to the human brain from three sets of receptors in the retina called cones, which are especially sensitive to red, blue, and green.
Our eyes ability to perceive color varies from one individual to another in some extent (to a bigger extent in people with color abnormalities.)

Front 50

Signals of color are sent to the human brain from three sets of receptors in the _____ called ______, which are especially sensitive to _____, ____, and _____.

Back 50

Retina; cones
red, blue, and green.

Front 51

Colorimeter

Back 51

a scientific instrument that measures the intensities and wavelengths of light. Although colorimeters are more precise than the human eye in measuring slight differences in colored objects, they are inaccurate for rough or curved surfaces. The eye is highly sensitive in comparing two colors seen side by side, whether on rough, smooth, flat, or curved surfaces. Colorimeter is best for lab values, but visual (Munsell) is more important.

Front 52

Colorimeters are inaccurate for

Back 52

round or curved surfaces

Front 53

Colorimeter is best for

Back 53

lab values, but visual (Munsell) is more important.

Front 54

It takes a difference of at least ΔE* = ___for a person to perceive a difference in color.

Back 54

3.3
ΔE* = [(ΔL*)2+(Δa*)2+(Δb*)2]1/2
ΔE* >3.3 is clinically detectable

Front 55

ΔE =

Back 55

Color Shift, can use for color matching purposes – if distance between “color coordinates” is less than 3.3, it matches.

Front 56

Teeth can be the same exact size, but lighter looks_______, smooth/gloss looks ______.

Back 56

larger, larger

Front 57

Polymer

Back 57

“poly” = many, “mer” = unit/part. A molecule that consists of many repeating units arranged in an extremely long chain. Shorter versions (approx. less than 10 units) are called oligomers.

Front 58

Monomer

Back 58

Chemical compound capable of reacting to form a polymer.

Front 59

Polymerization:

Back 59

A chemical reaction in which monomers (low molecular weight) are converted into polymers (high molecular weight)

Front 60

Applications of polymers in dentistry:

Back 60

 Prosthesis (dentures base acrylic)
 Restorations (filling resins)
 Equipment (mixing bowls)
 Impression materials
 Denture liners
 Cements (resin based)

Front 61

Factors that determine the properties of polymers:

Back 61

• Molecular structure
• Chain structure
• Side-groups
• Crosslinking

Front 62

Chain length/ Molecular Weight;
The longer the polymer chain, the ______ the number of entanglements (temporary connections) among chains. The longer the chains, the ______ difficult it is to distort the polymeric material

Back 62

greater; more

(think of his branch in a bush analogy: a short stick in a bush would be easier to pull out than a longer branched out branch/stick). Therefore, rigidity, strength, and melting temperature increase as well.

Front 63

Branched and cross-linked polymers have _________ material/mechanical properties compared to linear polymers.

Back 63

stronger

Front 64

Crystalline Regions

Back 64

highly ordered
Hard and rigid
High melting point
Impermeable
Transparent or translucent

Front 65

Amorphous Regions

Back 65

Random coils
Soft and flexible or glassy
Low glass transition T
Absorbs liquids
Transparent

Front 66

Combination

Back 66

Translucent or opaque

Front 67

Molecular organization affects material and mechanical characteristics. In some polymers, the chains can align themselves to form a highly ordered (________) structure. In others, the chains are randomly coiled and entangled in a very disordered pattern known as an ________ structure. Many polymeric materials combine these 2 forms of organization.

Back 67

(crystalline)
“amorphous”

Front 68

Elastic Materials

Back 68

Easily deformed but rapidly returns to the original shape. Elastic recovery occurs in the amorphous regions of polymers when the randomly coiled chains straighten and then recoil and return to their original location in the material. This behavior can be described as spring-like, and it is fast and reversible.

Front 69

Elastic Recovery

Back 69

 Easily deformed but rapidly recovers
 Occurs in amorphous regions
 Chains uncoil but do not slip

Front 70

Elastic recovery occurs in the _____ regions of polymers when the randomly coiled chains straighten and then recoil and return to their original location in the material

Back 70

amorphous

Front 71

Plastic Material

Back 71

Readily deformed and molded into a new, permanent shape (similar to stretching or deforming putty). It occurs because polymer chains slide over one another and become relocated within the material, resulting in permanent deformation. Plastic flow is like a shock absorber (slow, irreversible). Chains slip past one another but don't uncoil.

Front 72

Plastic material occurs because _______ chains slide over one another and become relocated within the material, resulting in _______ deformation.

Back 72

polymer; permanent

Front 73

Plastic Deformation:

Back 73

 Readily deformed and molded
 Permanent
 Chains do not uncoil
 Chains slide past each other
 Irreversible

Front 74

 Thermoplastics

Back 74

 Soften when heated
 Reversible
 No chemical bonds formed

Front 75

Thermoplastics are ______ (reversible or irreversible)?

Back 75

Reversible

Front 76

 Thermosets

Back 76

 Crosslinked polymers
 Crosslinking bonds prevent flow
 Irreversible

Front 77

Thermosets are ____ (reversible or irreversible)?

Back 77

Irreversible

Front 78

 Glass Transition Temperature (Tg)

Back 78

 Transition T from glassy to rubbery state
 NOT melting
 Sudden alteration in the rate of change of specific volume

Front 79

When a solid polymer is ______ enough, it is stiff, hard and brittle, and is called _______.

Back 79

cold; glassy

Front 80

When a material is heated, it's _______ behavior changes

Back 80

mechanical

Front 81

At a certain temperature, called the _____ ______ _____, there is a marked change from being glassy and brittle to distinctly _____ or _______.

Back 81

glass transition temperature (Tg);
ductile or rubbery

Front 82

Tg is

Back 82

a principal characterizing property of a polymer and is defined in various ways. It is the temperature where the polymer goes from a glassy to a ductile state. It can also be defined as the temperature where there is a sudden alteration in the rate change of specific volume.

Front 83

At low temperatures, the stiffness of primary valance bonds dominates the behavior, and at high temperatures, ____ _____ gives a very low modulus.

Back 83

chain slippage

Front 84

On the log (E/Pa) graph, Each step down with rising temperature corresponds to the _______ of a particular type of molecular motion.

Back 84

"unfreezing"

Front 85

Viscoelastic

Back 85

Plastic "flow" and elastic recovery both occur in real polymers.

• Chain length
• Number of crosslinks
• Temperature
• Rate of force application (impact versus squeezing)
…all determine which type of behavior dominants.

Front 86

Viscoelastic determinants

Back 86

• Chain length
• Number of crosslinks
• Temperature
• Rate of force application (impact versus squeezing)

Front 87

Plastic and elastic properties describe ____materials. However, real polymeric materials always recover with a combination of elastic and plastic changes. _______ always have a small degree of permanent deformation, while _____ always show some a small degree of elastic recovery after deformation.

Back 87

ideal; Elastomers; plastics

Front 88

Polymers tend to ______ a solvent, swell and soften rather than ______, but as chain length decreases, they will ______.

Back 88

absorb; dissolve; dissolve

Front 89

The longer the chains, the _____ a polymer dissolves

Back 89

slower

Front 90

Crosslinking prevents complete chain separation and ______dissolution.

Back 90

inhibits

Front 91

Highly cross-linked polymers ______ be dissolved

Back 91

cannot

Front 92

Amorphous polymers swell more than _______ polymers.

Back 92

crystalline

Front 93

Elastomers swell ______ than plastics

Back 93

more

Front 94

Monomers add sequentially one to another in a reaction. Polymers produced by this method are a simple multiple of the monomer

Back 94

chain-growth; simple

Front 95

Additional Polymerization (4 Processes)

Back 95

Activation, initiation, propagation, termination

Front 96

Activation

Back 96

initiator--->free radical

Front 97

Initiation

Back 97

free radical + monomer ----> Activated monomer
Benzoyl Peroxide ---> R:

Front 98

Propagation

Back 98

Activated monomer + monomer ---> growing chain
R-MMA: + MMA ---> R-[MMA]2 ----> + nMMA --> R-[MMA]n+1

Front 99

Termination

Back 99

R-[MMA]n+1 + :MMA-R ----> R-[MMA]n+1-MMA-R

Front 100

Condensation Polymerization

Back 100

Step growth polymerization
Monomers react simultaneously
Catalyst used
Small molecules condensed out (water, HCL)

Front 101

In condensation polymerization, monomers react

Back 101

simultaneously

Front 102

Accelerator

Back 102

a catalyst that makes the initiator unstable at ambient (i.e., normal) temperatures.
Therefore, additional heat is not needed.

Front 103

Accelerator characteristics

Back 103

• usually aromatic amines.
• always found in "self"-curing (also called "cold"-curing) polymer resin systems.
• must be mixed with the initiator (“catalyst”) before polymerization will begin. Thus, two part systems are used. One part has the initiator, the other the accelerator.

Front 104

Accelerators must always be found in ___ ____ polymer resin systems

Back 104

self-curing

Front 105

Accelerators must be mixed with the _____ before polymerization will begin.

Back 105

the initiator

Front 106

Inhibitor

Back 106

an additive that reacts with free radicals faster than do monomers. Free radical "scavengers."

Front 107

Inhibitor characteristics

Back 107

• delays initiation and allows for sufficient working time.
• acts like a preservative - extends storage life/"shelf life."
• typically a hydroquinone similar to food preservatives such as BHA & BHT

Front 108

An inhibitor acts like a ____, extends storage lift/shelf life

Back 108

preservative

Front 109

"Condensed" byproducts (such as H2O and HCl) degrade properties:

Back 109

• Evaporation leads to porosity & shrinkage
• Retention leads to plasticity (softening)

Front 110

Evaporation leads to

Back 110

porosity and shrinking

Front 111

Retention leads to

Back 111

plasticity (softening)

Front 112

Applications of Ceramics in Dentistry:

Back 112

• As teeth in full and partial dentures.
• “Jacket” crowns and inlays.
• Veneer over metallic restorations.

Front 113

CERAMICS

Back 113

Materials made from highly reacted (in their highest oxidation state) or otherwise inert chemical compounds - usually metal oxides, e.g.: MgO, SiO2, Al2O3

Front 114

Characteristics of Ceramic Materials:

Back 114

• Extremely stable, mostly ionic, bonds
• High melting temperatures
• Hard and brittle
• Low thermal expansion and contraction
• Electrical insulators
• Colorless
• Thermal insulators

Front 115

Chemical stability of Ceramics:

Back 115

• Inert - does not corrode or react
• Insoluble
• Highly oxidized
• Biologically compatible

Front 116

Porcelain

Back 116

Multiphase ceramic with crystalline phases dispersed in a glass.
• Glass phase binds crystalline phases together.
• Fabrication by thermal fusion of ceramic "frit", particles (a frit is, essentially, a form of ground-up glass)
• Translucent or opaque

Front 117

Glass

Back 117

• An amorphous, single phase, ceramic – "vitreous."
• Short range order, no long range order
• Melting range (not a melting point)
• Transparent
• A plastic-like material with a very high degree of thermal stability

Front 118

What is a plastic-like material with a very high degree of thermal stability?

Back 118

Glass

Front 119

Positives of Ceramics

Back 119

• Extremely stable, mostly ionic, bonds
• High melting temperatures
• Inert - does not corrode or react
• Biologically compatible
• Insoluble
• Low thermal expansion and contraction
• Electrical insulators
• Colorless
• Thermal insulators
• Highly oxidized

Front 120

Negatives of ceramics

Back 120

hard and brittle

Front 121

Agglomerate particles into a "paste" (step one in making crowns)

Back 121

Water acts as an adhesive (via surface tension).

Front 122

Shape and Condense

Back 122

• Removes excess H2O, maximizes packing. Shape and size distribution determine attainable degree of packing among the frit particles.
• Vibrate, blot or add more powder to remove excess H2O.
• Condensing determines shrinkage during later firing.

step two in making crowns

Front 123

Remove all water

Back 123

• Slow warming avoids steam build-up and blowouts.
Step 3 in making a crown

Front 124

Fire

Back 124

Step four in crown making

• Heat to temperature where the flux begins to liquefy.
• Liquid bridges begin to form between the frit particles.

Front 125

Sintering

Back 125

fusion of solid particles by heat and pressure

Front 126

Build up and refire

Back 126

Step 5 in crown making

• Add in layered increments.
• Alterations: grinding & additions can be done at this stage
• Progressive fusing to attain:
maximum density
minimum porosity
maximum translucency
• During cooling porcelain solidifies and shrinks in proportion to its thermal expansion coefficient.
• The thermal coefficient of the 1st (“opaque”) layer must be slightly more than that of the next (“dentin”) layer.

Front 127

Each subsequent layer of porcelain must shrink somewhat ______

Back 127

less (i.e., have a smaller thermal expansion coefficient) than the layer below it.

Front 128

Thermal expansion coefficient reflects the ___ ____ ____ upon heating, as well as the ___ ___ _____ upon cooling

Back 128

rate of expansion; rate of contraction/shrinkage

Front 129

Characterization

Back 129

Step 6 in making crowns

• Final grinding should take place at or before this stage
• Addition of stains
• The purpose is to produce a natural appearance

Front 130

Final grinding should take place at this stage of crown making

Back 130

Characterization

Front 131

Glazing

Back 131

Step 7 in crown making

A final firing which produces a liquefied layer to cover the surface.
• Fills in surface defects and approximately doubles tensile strength
• Natural-appearing gloss (specular reflection)
• Firing at a still-higher temperature attains a “natural” glaze – but there is a risk of slumping!
• Special glazing porcelain can be applied. A glaze-forming layer requires a
• Reduced firing temperature, but will have
• Greater solubility.

Front 132

A glaze-forming layer requires a

Back 132

• Reduced firing temperature, but will have
• Greater solubility.

Front 133

The time and temperature, ______ and the use of _____ can all affect the end ceramic.

Back 133

over-firing and under-firing ; vacuum

Front 134

The more porous the material, the ____ translucent it is

Back 134

less

Front 135

Which stages are safe for grinding?

Back 135

Buildup and refire and characterization

Front 136

Brittleness

Back 136

A material that is strong in compression but weak in tension and shear.

Front 137

Brittle failure is due to lack of ______ - i.e., inability of dislocations to migrate to new, stable locations. Once started, cracks _____ in brittle materials.

Back 137

ductility; propagate

Front 138

Crack Initiation

Back 138

• Surface imperfections act to concentrate stress.
• Cracks are initiated when shear or tension is applied.
• When a brittle material is subjected to compression, surface openings/cracks are closed:
Brittle materials are strong in compression, but weak in tension.
Scratches and porosity are prime sources of surface imperfections – known as “Griffin flaws”.

Front 139

Brittle materials are ___ in compression, but ____ in tension.

Back 139

strong; weak

Front 140

Griffin flaws

Back 140

Scratches and porosity are prime sources of surface imperfections

Front 141

Approaches to strengthening Porcelain

Back 141

Surface treatments
Reinforcing particles
Ion exchange
Laminate Structures

Front 142

Surface treatments

Back 142

Glaze fills in imperfections, doubles strength.
• Grinding: scratches can reduce tensile strength by as much as half.

Front 143

Reinforcing Particles

Back 143

• High strength particles force crack through, or around them — thus using more energy.
• Quartz and alumina (aluminous porcelain)
• Opacity increased (more light scattering)

Front 144

Ion exchange

Back 144

Creates surface compression that must be overcome for a crack to propagate and cause failure. Therefore, tensile strength is greatly increased.

Front 145

Laminate Structures (layered)

Back 145

• Alumina or metal "copings"
• Most cracks tend to initiate on the internal, "fitting" surfaces.
• A metal understructure (coping) resists these tensile forces and thus prevents crack initiation.
• Metals used, include:
• gold alloys
• platinum foil
• palladium alloys
• Ni alloys

Front 146

• Thermal expansion coefficient of porcelain must be slightly ____ than that of the metal coping.

Back 146

Less

Front 147

Metal will shrink _____ than the porcelain and the porcelain/metal bond forces the porcelain layer to shrink – excessively – with the metal.

Back 147

more

Front 148

How is the porcelain layer strengthened?

Back 148

• Thus the porcelain is held under compression. Before a crack can be initiated, this compression must be overcome

Front 149

Subsequent layers of porcelain must also have _____ thermal expansion coefficients.

Back 149

decreasing

Front 150

Metals must have a ___ melting point than porcelain for PFM restorations

Back 150

higher

Front 151

Metals must have ____ thermal expansion than porcelain for PFM restorations

Back 151

Lower

Front 152

Metals must have an _____ surface for PFM restorations

Back 152

oxidizable

Front 153

Porcelain must have an ____ layer for PFM restorations

Back 153

opaque

Front 154

Fabrication process in PFM restorations

Back 154

Metal is sandblasted
Degas
Apply an opaque layer
Buildup
Matching thermal expansion

Front 155

Metal is sandblasted:

Back 155

• Makes a clean surface for wetting and adhesion
• And a roughened surface for mechanical interlocks

Front 156

Degas (removing gas) - The casting is heated to 1800°F (1000°C) in order to:

Back 156

step two in Fabrication process

Drive off any surface-adsorbed gases, and …
• Cause oxidizable elements to migrate to the surface (e.g., Fe, In, Sn), thus, providing:
• Higher surface energy
• Surface wettable by molten porcelain
• Stronger bonding

Front 157

Apply an opaque layer

Back 157

step 3 in fabrication
Thin layer of highly light-scattering porcelain, hides color of metal

Front 158

Buildup

Back 158

step 4 in fabrication process
One layer after another is added and fired, as with all-ceramic articles.

Front 159

Matching thermal expansion

Back 159

• During firing porcelain fuses and the metal expands.
• During cooling porcelain solidifies and both metal and fused porcelain shrink.
• Thermal expansion coefficient of porcelain must be slightly less than that of the metal coping. In this case the metal will shrink more than the porcelain and the porcelain/metal bond forces the porcelain layer to shrink – excessively – with the metal.
• Thus the porcelain is held under compression. Before a crack can be initiated, this compression must be overcome – in this way the porcelain layer is strengthened.
• Subsequent layers of porcelain must also have decreasing thermal expansion coefficients.

Front 160

In the Degas step of preparing metals for PFM restorations, you heat the metal cast to cause oxidizable elements to migrate to the surface (Fe, In, Sn) providing:

Back 160

• Higher surface energy
• Surface wettable by molten porcelain
• Stronger bonding

Front 161

During firing, porcelain fuses and the metal _____

Back 161

expands

Front 162

During cooling, porcelain solidifies and both metal and fused porcelain _____

Back 162

shrink

Front 163

Temperature is used to control the expansion and contraction of both the metal and ______.

Back 163

ceramic

Front 164

Opaque layer

Back 164

The first layer placed on the metal copping of the PFM crown is the opaque layer. It’s a thin layer of highly-light scattering porcelain, hides color of metal.

Front 165

Body layer & Enamel layer

Back 165

intermediate layers, the body layer being the primary shade of the crown as well as the thickest, and the enamel layer being thinner, providing a more translucent natural appearance. ???

Front 166

Glaze

Back 166

This is part of the final firing, which produces a liquefied layer to cover the surface.
Fills in surface defects and approximately doubles tensile strength. Gives a natural-appearing gloss (specular reflection)

Front 167

CAD/CAM

Back 167

Computer Assisted Design/Computer Assisted Machining (Aided can also be the “A”). This allows ceramics to be milled (machined) to form inlays, onlays, and veneers.

Front 168

Advantages of CAD/CAM

Back 168

• Quick turn-around from a lab (or lab doesn’t even have to be involved)
• Can produce restorations in one office visit
• Bonding of ceramic restorations with resin cements helps compensate for the problems of poor marginal fit.
• Fracture of ceramic restorations can be prevented if the preparation has adequate thickness to resist occlusal forces.
• No need for impressions
• Restorations are natural looking

Front 169

Disadvantages of CAD/CAM

Back 169

• Marginal accuracy - can be poor, with values of 100-150 um
• Longevity - is less than PFM crowns
• Durability - Excellent for inlays; however full posterior crowns tend to break within 4 years
• Color match is limited – ceramic blocks are difficult to color match
• Technically challenging – assistants are often intimidated by the CEREC technology
• High cost – CEREC system = $100,000

Front 170

Biomaterials

Back 170

Materials of natural or manmade origin that are used to direct, supplement, or replace
the functions of living tissues

Front 171

Biocompatibility

Back 171

The compatibility of manufactured materials and devices with body tissues and
fluids.

Front 172

Biological Performance:

Back 172

The interaction between materials and living systems. This includes both
the materials response and host response.

Front 173

Materials Response:

Back 173

The response of the material to living systems

Front 174

Host Response:

Back 174

The reaction of a living system to the presence of a material. These host responses
can be classified according to whether the material is biotolerant (elicit tolerable local host
response), bioinert (absence of local host response) or bioactive (elicit positive or desired local host
response).

Front 175

Reference Material:

Back 175

A material that, by standard test, has been determined to elicit a reproducible,
quantifiable host or material response.

Front 176

Initial events of inflammation (0-12hrs)

Back 176

During this stage cell degeneration and cell death happens, and tissue necrosis begins. This stage
can be characterized by cell swelling, loss of enzyme function, loss of semipermeability of
membranes, and pyknosis (reduction in size of cell and/or nucleus) and loss of nuclei. Degenerative
changes can be further separated into biochemical (happening within a few seconds) and functional
lesions (happening within a minute). This is followed by cell death (1 minute to 12 hrs) and necrotic
changes (12-24 hrs).

Front 177

Inflammation:

Back 177

Inflammation is a nonspecific physiological response to tissue damage in animal systems. It arises
as a response to trauma, infection, intrusion of foreign materials, or local cell death.

Front 178

Four signs of inflammation

Back 178

Redness, swelling, pain, heat

Front 179

Redness

Back 179

This reflects a higher local concentration of erythrocytes. Vasodilation of local
capillaries leading to an increase in blood entry into the capillary beds then occurs. Local aspect
ratio changes in the capillaries, combined with loss of plasma through the capillary walls and a
tendency for the platelets and erythrocytes to become "sticky" then leads to slower flow and sludging.

Front 180

Swelling

Back 180

As permeability of the endothelial cell lining increases due to an inflammatory
stimulus, water and larger molecules including plasma protein move into the tissue. If the
increased fluid influx is not promptly balanced by increased lymphatic drainage, swelling occurs.

Front 181

Pain

Back 181

Local swelling (edema) may activate local deep pain receptors. Secondly, kinins act
directly on nerve ends to produce pain sensation.

Front 182

Heat

Back 182

Local heating effect is associated with local disturbances of fluid flow in the presence of
increased cellular metabolic activity. Also, a group of contaminants termed pyrogens known to
cause systemic fever may be generated locally either by tissue necrosis, or in the presence of
infection, as a result of activation of bacterial or viral toxins, especially endotoxin.

Front 183

Immune Reaction:

Back 183

There are generally three different leukocyte cells acting against foreign materials in the tissue.

Front 184

Neutrophils

Back 184

These are the first leukocyte cells to appear at the site of injury. They contain
multilobed nuclei. Neutrophils begin to penetrate between the endothelial cells and move into
the surrounding damaged tissue sometimes within minutes, and may continue for as long as 24
hours. When in contact with a small enough foreign material, phagocytosis occurs. The
neutrophils are attracted by a particular chemical composition, by local pH differences or by
electrochemical factors associated with the foreign particle and their surroundings.

Front 185

Eosinophils

Back 185

They are also among the first cells to appear at the site of injury. Eosinophils are
very similar in structure and they perform a similar phagocytic function. However, they are
present in a far smaller number as compared to the neutrophils.

Front 186

Monocytes

Back 186

They are the largest of the freely circulating leukocytes. They are distinguished
from the neutrophils by its larger size and its single, centrally located large nucleus. Once in the
tissue, they become macrophages. They arrive at the site of injury after the neutrophilic invasion
has begun to subside and concentrates in appreciably smaller numbers. Their role is similar to
that of the neutrophils in that they can actively phagocytize materials and digest them.

Front 187

Other cells in immune reaction

Back 187

In addition, fibroblasts and angioblasts appear to form scar tissue or fibrous capsules
around the foreign material, as well as lymphocytes and plasma cells.

Front 188

Final events of inflammation

Back 188

Final events include the stages of tissue regeneration or wound repair. The body’s reaction to the
biomaterial in the above stages determines the biocompatibility of the material. Note that it is
possible to have a biocompatible material that exhibits minimal tissue response but no effect on the
final tissue repair or regeneration.

Front 189

Enamel response to injury

Back 189

Due to its highly mineralized structure, enamel is more brittle than dentin, and is
susceptible to being solubilized by acid solutions that may be released by biomaterials or cause to be
formed by the presence of the biomaterial whether directly or indirectly (via bacteria

Front 190

Dentin and Pulp response to injury

Back 190

Due to the presence of dentin tubules that are filled with odontoblastic processes
that traverse between the dentoenamel junction and the pulp, toxic bacterial or chemical products
that can pass through the enamel will be able to traverse the dentin and cause reactions from
odontoblasts and the pulpal connective tissue. Reactions may begin with focal necrosis (0-12 hrs)
that may be followed by an acute, but more widespread, pulpitis (12 hrs to several days). These
reactions may resolve naturally if the injurious agent is removed or the tubules are blocked. If the
pulpitis does not resolve, it may spread to more completely involve the pulp in liquefaction necrosis
or in chronic inflammation. Finally, both acute complete pulpitis and acute exacerbation of chronic
pulpitis may lead to sequelae such as dental periapical lesions and osteomyelitis.

Front 191

Periodontium response to injury

Back 191

When cells that maintain the periodontal ligament (PDL) are destroyed during injury
and have no source of progenitor cells, ankylosis may result between tooth and bone (e.g. after tooth
transplantation or placement of dental implants). In an attempt at regeneration, gingival epithelium
replaces cells originally responsible for the epithelium attachment of the tooth. Following scaling
and curettage of periodontal pockets, this gingival epithelium proliferates faster than the PDL fibers
can reattach in newly formed cementum. Although fibrous reattachment to alveolar bone appears to
occur quite readily, the original orientation of fiber to the tooth surface seems quite difficult to
achieve. This results in epithelial-lined subcrestal pockets in the PDL space between alveolar bone
and tooth surface.

Front 192

Gingiva and Muscosa response to injury

Back 192

In cases such as the presence of perimucosal implants, special problems
including epithelial ingrowth, encystification, and exfoliation of the implant are presented in gingival
tissues. Additionally, there is the problem of maintaining a close epithelium attachment between the
implant and soft tissue that excludes bacteria. Oral mucosa and gingiva are also susceptible to
immune hypersensitivity reactions when subjected to synthetic or natural materials that are
antigenic. Local binding of antigens to membranes of white blood cells (i.e. lymphocytes,
macrophages, basophils, mast cells) or Langerhan’s cells of skin and oral mucosal epithelium play a
role in activating these various reactions. Most reactions to dental materials are Type IV reactions
(T-cell mediated), also called contact mucositis.

Front 193

Bone response to injury

Back 193

If bone injuries are small and periosteal or endosteal damage is not severe, the usual
mechanism for bone repair is membranous bone formation. Granulation tissue is formed from the
surrounding vascularized connective tissue to fill the bony defect. New osteoblasts, derived from
precursor cells in residual periosteum or endosteum, secrete collagen-rich osteoid, which is
subsequently mineralized and remodeled. For cases involving implants, the desire is for the alveolar
bone to integrate the material into the remodeled bone, rather than forming a fibrous tissue capsule.

Front 194

Initial biocompatibility test

Back 194

These tests are carried out in two basic stages: In vitro (involving cell culture) and in vivo (involving
the use of animal models). In vitro tests may use either primary cells (cells taken directly from animals to culture) or cell lines (primary cells transformed to allow them to grow more or less indefinitely in culture).

Front 195

Cytotoxicity assays:

Back 195

These tests measure the
effects of a material on 1) cell number or
growth, 2) integrity of cell membranes, 3)
biosynthesis or enzyme activity, or 4) the
genetic material of the cell.

Front 196

Advantages of cytotoxicity assays

Back 196

1) the ability to test for a
specific function of cell metabolism in
isolation from other events, 2) ability to
screen large numbers of samples quickly and
inexpensively, 3) quantifiable results, 4)
greater sensitivity to toxic materials than
usage tests, and 5) standardization of test
methods.

Front 197

Disadvantages of cytotoxicity assays

Back 197

1) limitations of
testing to only one cell type at a time, and 2)
a lack of inflammatory and other tissue
protective mechanisms in tissue culture. Thus, this test alone cannot predict the overall
biocompatibility of a material.

Front 198

Cell number and growth tests:

Back 198

Measures cytotoxicity by measuring cell number or growth after
exposure to a material. Cells are plated in a well of a cell culture dish where they attach. The
material is then placed in the test system. If the material is not cytotoxic, the cells remain attached to
the well and will proliferate. If the material is cytotoxic the cells may stop growing, exhibit
cytopathic features or may detach from the well (Figure 1). If the material is solid, then the density
of cells may be assessed at different distances from the material and a “zone” of inhibited cell
growth may be described

Front 199

Membrane permeability tests:

Back 199

Membrane
permeability is the ease with which a dye can
pass through a cell membrane. Either vital
dyes (those that are actively transported into
viable cells but released when cytotoxic
effects increase membrane permeability) or
nonvital dyes (those only taken up by the cell
if membrane permeability has been
compromised due to cytotoxicity) can be
used (Figure 3). Examples of vital dyes
include neutral red and Na2
51CrO4, while examples of nonvital dyes include trypan
blue and propidium iodide.

Front 200

Biosynthetic or enzymatic activity tests:

Back 200

These tests measure DNA or protein
synthesis usually by adding radioisotopelabeled
precursors to the medium followed
by quantification of radioisotope (e.g. 3Hthymidine).
A commonly used enzymatic
test is the MTT test that measures how well
cellular dehydrogenases convert MTT to a
blue formazan compound, which happens
best in healthy cells

Front 201

Barrier Tests

Back 201

The above cytoxicity tests are
performed with the material in direct contact
with the cells, but in vivo direct contact often
does not exist between cells and materials, so
in vitro barrier tests were developed.

Front 202

Agar overlay test:

Back 202

Agar plus a vita stain
is added on top of a monolayer of
cultured cells forming a barrier between the cells and the material. Nutrients, gas, and soluble
toxic substances are allowed to diffuse through the agar for up to 24 hours

Front 203

Millipore filter assay:

Back 203

This assay is similar to the agar overlay test but cells are cultured on filters
made of cellulose esters. Then the agar is allowed to gel over the cells. Finally, the filtermonolayer-
gel is detached and turned over so that the filter is on top for placement of solid or
soluble test samples for 2 or more hours. Cytotoxicity is again assessed by the width of the
cytotoxic zone around each test sample.

Front 204

Dentin barrier test:

Back 204

Specific for dental materials, this test has improved correlation with the
cytotoxicity tests and usage tests in teeth because dentin forms a barrier that toxic materials must
diffuse through to reach pulpal tissue. Thus, this assay incorporates dentin disks between the test
sample and the cell assay system

Front 205

Mutagenesis assays

Back 205

These assays assess the effect of materials on a cell’s genetic material.
Genotoxic mutagens directly alter the DNA of the cell through various types of mutagens.
Epigenetic mutagens do not alter the DNA, but support tumor growth by altering the cell’s
biochemistry, altering the immune system, acting as hormones or other mechanisms. Carcinogenesis
is the ability to cause cancer in vivo. Mutagens may or may not be carcinogens and visa versa.
Thus, these tests are very complex and a specific order of tests is performed and stopped when any
one indicates mutagenic potential of the material or chemical. These tests are generally divided into
in vitro genotoxic short-term tests (STTs), limited term in vivo tests, and long-term or lifetime tests.
The ANSI/ADA Document 41 describes only two such tests: the Ames' test and the Styles' Cell
Transformation test, but there are more that may be added to the ADA specifications.

Front 206

Ames' test:

Back 206

This is the most widely used STT that is thoroughly validated. It uses mutant stocks of
Salmonella typhimurium as test cells. This test is sensitive to only 45% of the carcinogens.

Front 207

Styles' cell transformation test:

Back 207

This test uses transformed mammalian fibroblasts, and quantifies the
ability of potential carcinogens to transform the cells to grow in soft agar. Normal fibroblasts will
not grow in soft agar, and this has been correlated with the ability of cells to produce tumors in vivo

Front 208

Other assays

Back 208

Other assays not described in the ADA document include those that test to see if
materials alter immune cell function by measuring cytokine production by lymphocytes and
macrophages, lymphocyte proliferation, chemotaxis or T-cell rosetting to sheep red blood cells.
Other tests measure the ability of materials to alter the cell cycle or activate complement. Finally,
there are oral and intraperitoneal LD50 tests that determine acute lethal effects of agents in rats. LD50
is the dose required to kill 50% of the animals. If it is less than 1 g/kg body mass, the material is
considered to exhibit acute systemic toxicity.

Front 209

Secondary tests

Back 209

A series of longer-term test usually performed on animal models to identify inflammatory reactions
or immune reactions to the material

Front 210

Mucous membrane irritation test:

Back 210

Determines if the material causes inflammation of mucous
membranes or abraded skin when applied directly to hamster cheek pouch tissue or rabbit oral tissue
for several weeks.
Secondary test

Front 211

Skin sensitization test

Back 211

Secondary test
Agents are injected intradermally to test the development of skin
hypersensitivity reactions in guinea pigs. This injection is followed by secondary treatment with
adhesive patches containing the test substance. If there is hypersensitivity, the patch will elicit an
inflammatory response.

Front 212

Implantation tests:

Back 212

secondary test
These tests are used to evaluate materials that will contact subcutaneous tissue or
bone. The location of the implant site is determined by the use of the material. Short-term studies
are from 1-11 weeks of implantation while longer-term studies can be as long as 1-2 years.

Front 213

Usage Test:

Back 213

Test performed in animal models to identify all the effects of dental materials on the tissues in which
they will be used. These tests differ from secondary tests because the material must be placed and
used in the same function in the animal, as it will in the human. These tissues generally are the
dental pulp, gingival or mucosal tissues, and the tissues of the periodontium. Most usage tests of
dental materials have involved intact and noncarious teeth, presumably without inflamed pulps.

Front 214

Dental pulp irritation tests:

Back 214

Usage test
Materials to be tested are placed in class 5 cavity preparations in intact,
noncarious teeth of monkey or other suitable animals for 1-8 weeks. At the conclusion of the study,
the teeth are assessed for necrotic and inflammatory reactions.

Front 215

Dental implants into bone:

Back 215

Usage test
Success of implants is measured using the following 3 tests: Penetration
of a periodontal probe along the side of the implant, mobility of the implant, and radiographs
indicating either osseous integration or radiolucencies around the implant. An implant is considered
successful if it exhibits no mobility, no radiographic evidence of peri-implant radiolucency, minimal
vertical bone loss, and absence of persistent peri-implant soft tissue complications.

Front 216

Mucosa and gingival usage tests:

Back 216

Usage test
A class 5 cavity is usually prepared after dental prophylaxis is
performed. The test material is then placed in the cavity preparation with subgingival extension.
The material's effects on gingival tissue are observed at 7 days and again after 30 days.

Front 217

In vitro cytotoxicity tests
can at best estimate the _____ _____ and ______ events (first 12-24 months) but not the
______ or _______ reactions of tissue.

Back 217

initial degenerative and necrotic;
inflammatory or chronic

Front 218

Secondary and usage tests measure _____ _____ ____ and necrosis, as well as ________ and immune reactions.

Back 218

host
cell degeneration; inflammatory

Front 219

Dentin Bonding Agent:

Back 219

Bonding restorative materials to dentin causes biocompatibility issues because the dentinal tubules
and their resident odontoblasts are extensions of the pulp and so are exposed to the dentin bonding
agents. While there are several different types of bonding agents, it is suggested that residual
unbound reagents were the cause of any cytotoxcity.

Front 220

Resin-Based Materials:

Back 220

Bis-GMA is the most widely used restorative resin, but even in such a resin there are many different
chemicals. However, it is thought that only three of the ingredients (2-hydroxy-4-benzophenone,
9
benzoyl peroxide, and methyl ester of benzoin) caused pupal reactions. More recently the estrogenic
effect of Bisphenol-A (BPA), a component and possible degradation product of Bis-GMA and Bis-
EMA has been under scrutiny.

Front 221

Amalgams and Cast Alloys:

Back 221

in cell culture, free or unreacted mercury from amalgam is toxic, but low-copper amalgam
that was set for 24 hours does not inhibit cell growth. Implantation tests showed that low-copper
amalgams are well tolerated, but high-copper amalgams caused severe reactions. Amalgams based
on gallium rather than mercury have been developed but cell culture tests showed that this was as
cytotoxic as traditional high-copper amalgams, and in implantation tests, gallium alloys caused
significant foreign body reaction.

Front 222

Glass Ionomers:

Back 222

Glass ionomers have been used both as cements (luting agent) and as restorative materials. The
material is a product of the reaction of a polymer acid and a fluoride-containing calcium
aluminosilicate glass. In screening tests, these materials were mildly cytotoxic, but this effect is
reduced with increased times after setting. In usage tests, the pulp reaction to these materials is mild.

Front 223

Calcium Hydroxide Cavity Liners

Back 223

The high pH of these materials in suspension leads to extreme
cytotoxicity in screening tests. Calcium hydroxide cements containing resins cause mild-tomoderate
cytotoxic effects in tissue culture in both the freshly set and long-term set conditions.
When resins are incorporated into these materials, they become less irritating and are able to
stimulate reparative dentin bridge formation. Thus, they are the most effective liners now available
for treating pulp exposure.

Front 224

Zinc Phosphate

Back 224

These have been the most widely used dental cements for castings, orthodontic
bands and to base cavity preparations. In vitro screening tests indicate that these cements elicit
strong-to-moderate cytotoxic reactions that decrease with increased time after setting. Implantation
tests confirm this with the presence of focal necrosis when injected into rat pulp. In usage tests in
deep preparations, moderate-to-severe localized pulpal damage is produced within the first 3 days.
By 5-8 weeks, only mild chronic inflammation is present and reparative dentin has usually formed.

Front 225

Zinc Oxide Eugenol Cements:

Back 225

In vitro, eugenol fixes cells, depresses cell respiration, and reduces
nerve transmission with direct contact. Surprisingly, it is relatively innocuous in usage tests in class
5 cavity preparations.

Front 226

Zinc Polyacrylate Cements:

Back 226

These cements were developed to combine the strength of zinc
phosphate cements with the adhesiveness and biocompatibility of zinc oxide-eugenol. In short term
tissue culture tests, cytotoxicity of freshly set and completely set cements has correlated both with
the release of zinc and fluorides into the culture medium and with reduced pH. Implantation tests
over a year long have not shown any cytotoxicity.

Front 227

Bleaching Agents:

Back 227

In vitro peroxides can be cytotoxic, but it depends on the concentration of peroxide in bleaching
agents. In vivo, there are few studies that have demonstrated adverse pulpal effects from bleaching

Front 228

Metals as implant materials

Back 228

Metal implants/restorative materials were first developed because of their strength. The
following events can happen at the oxide surface when metal is exposed to a biological environment.

Front 229

Oxidation:

Back 229

The direct reaction of metal with oxygen, either gaseous or dissolved, without the
participation of water. This oxide layer can alleviate problems associated with corrosion and
enhance biocompatibility as in the case with titanium

Front 230

Hydroxide formation

Back 230

Oxygen and hydrogen can diffuse into the oxide forming hydroxide that
may contribute to reactions to the material.

Front 231

Incorporation of mineral ions:

Back 231

Minerals can diffuse or adsorb on the surface. The rate of
diffusion is dependent on the temperature.

Front 232

Dissolution of oxide metal ions (Corrosion):

Back 232

Refers to dissolution in the presence of a solution.
Both oxidation (metals going into solution) and reduction (consumption of electrons) has to take
place for corrosion to occur. Factors affecting corrosion include stability and thickness of oxide
layer, pH, temperature, and proteins. Corrosion causes adverse inflammatory reactions.

Front 233

Biomolecule adsorption/desorption or replacement:

Back 233

Biomolecules such as proteins continuously
adsorb and desorb at the implant biomaterial surface. Competitive adsorption of proteins
(replacement) has also been observed to occur.

Front 234

Water molecule adsorption

Back 234

Similar to biomolecule adsorption, water molecule adsorption
occurs at biomaterial surfaces. Increased wetting has shown to increase biocompatibility with
certain materials.

Front 235

Activation

Back 235

Initiator ---> Free radical
Benzoyl Peroxide ---> R:

Front 236

Ceramics as implant materials

Back 236

Ceramics are already in an oxidized state, which allows them to be chemically stable and
corrosion resistant. They are extremely biocompatible, nonimmunogenic, and noncarcinogenic.
However, they are brittle and lack impact and shear strength

Front 237

Polymers as implant materials

Back 237

The oldest polymer used as implants is the polymethyl methacrylate (PMMA). PMMA is
not inert and leaching of products results in chronic irritation of the surrounding connective tissue
with persistence of chronic inflammatory cells, a fibrous capsule to isolate the implant, and no bone
adaptation. Problems associated with PMMA include cytotoxicity of residual monomer present and
high polymerization temperature.

Front 238

Biotolerant

Back 238

elicit tolerable host response

Front 239

Bioinert

Back 239

absence of local host response

Front 240

Bioactive

Back 240

elicit positive or desired local host response

Front 241

Initial events after injury (0-12hr)

Back 241

cell degeneration, death, and necrosis

Front 242

Tissue response(12hr-1wk)

Back 242

Inflammation then Immune

Front 243

Final events (1wk-6wk)

Back 243

Regeneration and repair

Front 244

How do usage tests differ from secondary tests?

Back 244

These tests differ from secondary tests because the material must be placed and
used in the same function in the animal, as it will in the human.

Front 245

An implant is considered successful if it exhibits

Back 245

no mobility, no radiographic evidence of peri-implant radiolucency, minimal
vertical bone loss, and absence of persistent peri-implant soft tissue complications.

Front 246

Types of Secondary Tests

Back 246

Mucous membrane irritation test
Skin sensitization test
Implantation test

Front 247

Types of Usage tests

Back 247

Dental pulp irritation test
Dental implants into bone
Mucos and gingival usage tests

Front 248

Stages of initial tests

Back 248

in vitro (involving cell culture)
in vivo (involving use of animal models)

Front 249

What three ingredients cause pupal reactions in Resin-based materials

Back 249

2-hydroxy-4-benzophenone,
9
benzoyl peroxide, and methyl ester of benzoin

Front 250

What are the most effective liners now available for treating pulp exposure?

Back 250

Calcium hydroxide cavity liners

Front 251

What are the most widely used dental cements for casting, orthodontic bands, and to base cavity preparations?

Back 251

Zinc phosphate cements

Front 252

Quartz

Back 252

Crystalline SiO2
• Present in small proportions
• Imparts strength and high melting temperatures
Ingredient used to form dental porcelains

Front 253

Feldspar

Back 253

Ingredient used to form dental porcelains
Two varieties: soda-ash (Na2O) and pot-ash (K2O)
• K2O•Al2O3•6SiO3 or Na2O•Al2O3•6SiO3
• Called a "flux"
• Liquefies and fuses frit particles together, when "fired"
• Proportion: ~85% of the porcelain
• Increasing the proportion of either K2O or Na2O results in:
 Decreased fusing temperature
 Softer glassy phase
 Increased solubility

Front 254

• Increasing the proportion of either K2O or Na2O results in:

Back 254

Decreased fusing temperature
 Softer glassy phase
 Increased solubility

Front 255

Kaolin

Back 255

Composition is Al2O3•2(SiO2•H2O)
• Present in dental porcelain formulations in only a few percent
• A clay
• Function is to increase viscosity (decreases flow) of the liquefied portion of the frit during
firing and thus prevent "slump"

Ingredient used to form dental porcelains

Front 256

Pigments

Back 256

Ingredient used to form dental porcelains
• Metal oxides – Fe2O3, CdS
• Provide color for shade matching