Dental Materials 3 D

Front 1

Properties of materials can be divided into three categories ----, ----, -----

Back 1

: physical, chemical, biologic

Front 2

based on the laws of physics that describe mass, energy, force, light, heat, electricity, and other physical phenomena. Examples are Color, density, and thermal conductivity

Back 2

Physical properties

Front 3

a subgroup of physical properties.

describe a material’s ability to resist forces.

Examples are strength and stiffness.

Back 3

Mechanical properties

Front 4

Mechanical properties are dependent on the ----- of material and on the --- and --- of the object.

Back 4

amount, size and shape

Front 5

describe the setting reactions as well as the decay or degradation of materials.

Back 5

Chemical properties

Front 6

the effects the materi-als have on living tissue.

Back 6

Biologic properties

Front 7

The amount or mass of a material in a given volume

Back 7

density

Front 8

A common unit of den-sity is ----. Density depends on the --- of atoms that are present (as the atomic number ----, so does the ----), the packing ---- of atoms and molecules, and the ---- in the material.The high density of most metal objects makes them feel ----. Most metals have high atomic numbers, and their atoms are packed closely together into ----.

Back 8

g/cm3, type, increases, density,together, voids, heavy, solids

Front 9

Boiling and melting points are ---- proper-ties of materials. They can be used to help identify chemicals. Mixtures often have a melting or boiling ---- rather than a specic melting or boiling point. When an object melts or boils, the atomic bonds between the atoms or molecules are broken by the ---- of the material. Some dental metals melt at very high temperatures and are very dif-cult to work with. Other materials do not boil or melt; instead, they ---- if heated suffciently.

Back 9

physical, range, thermal energy, decompose

Front 10

---- are an example of mixtures with a melting range. ---- and ---- are common examples of materials that decompose.

Back 10

Dental waxes, wood, cookie dough

Front 11

a measure of a liquid’s tendency to evaporate and become a gas.

Back 11

Vapor pressure

Front 12

As the temperature of a liquid ----, the vapor pressure ----. Materials with a low vapor pressure, such as cooking oil, do not evaporate ----. Materials with a high vapor pressure, such as rubbing alcohol, evaporate readily at ----

Back 12

increases, increases, quickly, room temperature.

Front 13

Materials with a high vapor pressure are very useful as ---- in the application of viscous (syrupy) liquids, such as glue or paint. The viscous liquid is ---- by mixing it with a solvent. The “more runny” mixture is then applied to a surface. As the solvent evaporates, it leaves behind a thin layer of the ---- .

Back 13

solvents, “thinned”, viscous liquid

Front 14

-----, a component of dental acrylic resins (plastics), has a high vapor pressure and can evaporate easily when a denture is processed. ---- may result, weakening the denture. Denture processing techniques are designed to minimize the evaporation of methyl methacrylate and the resulting porosity,

Back 14

Methyl methacrylate, Porosity

Front 15

the rate of heat flow through a material.

Back 15

Thermal conductivity

Front 16

Measurement of thermal conductivity depends on the ---- the heat travels, the ---- in which the heat travels (much like the size of the pipe throughwhich water travels), and the difference in ---- between the source and destination.

Back 16

distance, area, temperature

Front 17

Because thermal conductivity is a rate, it is measured as ---- over ----. Thermal conductivity is measured as -----.

Back 17

heat flow, time, calories/second·meter· degree.

Front 18

Pulpal sensitivity is likely if ---- materials, such as metals, are placed in close proximity to the ----. If caries are deep and a metal restoration is planned, an ---- is placed beneath the metal restoration to insulate the pulp from hot and cold stimuli.

Back 18

conductive, pulp, insulating base

Front 19

a measure of the amount of thermal energy that a material can hoard.

Back 19

heat capacity

Front 20

the amount of energy needed to raise the temperature of one unit of mass of that material by 1°C

Back 20

spe-cic heat capacity

Front 21

Some materials require more --- than others to heat. Specificc heat capacity is measured as ---. The heat capacity of water is ----

Back 21

energy, cal/g · deg, 1 cal/g · deg

Front 22

the amount of energy required to melt a material.

Back 22

heat of fusion

Front 23

the amount of energy required to boil a material.

Back 23

heat of vaporization

Front 24

heat of fusion and heat of vaporization are typically large in relation to the ----.

Back 24

heat capacity

Front 25

The heat of fusion of metals must be --- when melting gold for casting a crown. The solid metal must be heated to the melting temperature, and then a signican't amount of ---- must be added to melt the metal.

Back 25

overcome , energy

Front 26

Nearly all materials when cooled ---- or -----. On the other hand, most materials ---- when heated.

Back 26

shrink, contract, expand

Front 27

a measure of this change in volume in relation to the change in tem-perature.

Back 27

coefficient of thermal expansion

Front 28

The coefcient of thermal expansion is a fractional change in ---- or -----. Larger objects of the same material expand more in --- than smaller objects do, but larger objects expand by an ---- amount in terms of the percentage or fractional change.

Back 28

volume, length, quantity, equal

Front 29

Our interest in the coefcient of thermal expan-sion of dental materials is in relationship to those of --- and ----. the restorative materials of today more closely match the coefcient of thermal expansion of teeth. When the mismatch is great, the restoration will shrink with cold beverages, opening --- between the restoration and the tooth. When the tooth heats up again and expands, the gap is ---.

Back 29

enamel, dentin, gaps, closed

Front 30

The process of heating and cooling, and the accompanying opening and closing of the gap,

Back 30

percolation

Front 31

Percolation results in ----, ---- and -----.

Back 31

microleakage, tooth sensitivity, recurrent decay.

Front 32

--- are good electrical conductors. ---- and ---- are poor conductors and are termed ----. During electrosurgery or electronic pulp testing, it is important to know which restorations are conductive and which are not. Electrical conductivity also affects ----.

Back 32

Metals, Polymers, ceramics, insulators, corrosion

Front 33

Occasionally, a new amalgam filling will hurt when it is touched with a metal fork. This ---- is the result of electricity flowing from the --- to the --- and through the ----.

Back 33

galvanic shock, fork, amalgam, pulp

Front 34

ability of a material to flow

Back 34

viscosity

Front 35

When placing materials, the ---- of those materials are important. Some materials should --- easily and wet the surface. Other materials need to be more like putty, which can be adapted or formed into a desired ---.

Back 35

handling characteristics, flow, shape

Front 36

Thick or viscous liquids flow ----, whereas thin liquids flow easily. Viscosity is a ---- property

Back 36

poorly, a temperature -dependent

Front 37

Viscosity is measured as ---, or as ----. Water at 20°C has a viscosity of ---- or ----. Impression materials have viscosities between 100,000 and 1,000,000 cP.

Back 37

g/m·s, poise (P), 0.01 P, or 1 centipoise (cP),

Front 38

A low viscosity and the ability to --- a surface are important in the use of many dental materials. Wetting a surface with an adhesive material, such as a sealant, brings the material into intimate association with the surface so that ---- and --- bonding can occur. Wetting is measured by determining the ---- of a liquid on a solid,

Back 38

wet, chemical and micro mechanical, contact angle

Front 39

A low contact angle, such as that of a drop of water on a piece of ice, indicates --- wetting. A high contact angle, such as that of a drop of water on most plastics, indicates ---- wetting

Back 39

good, poor

Front 40

Another example of wetting in dentistry occurs when a gypsum product (plaster) is poured into an impression. If the mixed material wets the surface of the impression material, the --- of the impression will be reproduced in the cast. If poor wetting occurs, --- will likely result in insufficient detail and an unusable cast.

Back 40

fine details, bubbles

Front 41

---- is the hardest biologic tissue in the human body. Hard materials resist ---- and ---- by soft materials.

Back 41

Enamel, scratching, indenting

Front 42

a property that is measured by scientic instruments that press a special tip into the surface of the test material.

Back 42

hardness

Front 43

The tip has a characteristic shape made of a very hard material, such as --- or ----. The --- of the indentation created is then measured. --- is calculated based on the size of this indentation

Back 43

steel, diamond, size, Hardness

Front 44

What are methods used to measure hardness?

Back 44

Brinell method

Knoop method

Rockwell

Vickers hardness tests.

Front 45

The Knoop hardness number (KHN) of enamel is ---, whereas the KHN of dentin is ---. Some dental materials are harder than enamel. Porcelain has a KHN of --- to ---. Other materials are not as hard as enamel. For example, acrylic denture teeth have a KHN of ---.

Back 45

350, 70, 400, 500, 20.

Front 46

Some materials are --- and even ---. A different kind of hardness test is used for these materials because a surface hardness indentation will not occur. A --- measures how deep a steel ball will sink when pressed into the surface of a soft material.

Back 46

soft, spongy, durometer,

Front 47

Durometers are used to measure the hardness of --- materials and other ----.

Back 47

impression, elastic polymers

Front 48

Harder materials tend to be more resistant to --- than softer materials. In dentistry, we are inter-ested in the abrasion resistance (wear resistance) of dental restorations to ----, ---, and other dental materials such as --- or --- teeth. We are also interested in the wear of natural teeth opposing dental restorations.

Back 48

abrasion, food, opposing teeth, ceramic crowns, porcelain denture

Front 49

If a restorative material is too hard, it will ---- the opposing teeth at an unacceptably accelerated pace. Therefore, a restoration must be --- enough so that the restoration does not wear away, but not so hard as to excessively wear away the opposing teeth.

Back 49

wear, hard

Front 50

What is the Goldilocks principle?

Back 50

not too hard; not too soft; just right.

Front 51

More often than not, a material’s properties need to t within a particular --- of values, not the --- value, to be the material of choice.

Back 51

range, maximum

Front 52

Materials placed in the oral cavity are exposed to various --- fluids. The --- of materials in water is an important consideration.

Back 52

aqueous, solubility

Front 53

the amount of a material that dissolves in a liq-uid, such as water.

Back 53

Solubility

Front 54

---- materials should not appreciably dissolve in the mouth. Additionally, some materials tend to dissolve faster in ---- environments.

Back 54

Restorative, acidic

Front 55

To measure solubility, a test sample is immersed in ---. The --- of the material dissolved into the water is the solubility of that material. The solubility of some dental cements is measurable and clinically signicant. Excessive solubility leads to loss of --- and increases the risk of recurrent ---

Back 55

water, weight, material, decay.

Front 56

Some materials absorb water. This property is termed ---- . It is measured much like solubility. A test sample is immersed in ---, and the --- that is gained by that sample is the water sorption. When materials --- water, they tend to swell. Some materials both --- and --- water at the same time, making measurement of one of these properties difficult.

Back 56

water sorption, water, weight, absorb, dissolve, absorb

Front 57

The appearance of a restoration for an anterior tooth can be a factor when choosing materials. The --- and ---- of the restoration are important. In addition, the --- and --- of gingival tissues adjacent to a restoration are also noticed.

Back 57

color, surface luster, shape, health

Front 58

a complex phenomenon that is a psy-chological response to a physical stimulus.

Back 58

Color

Front 59

For color the physical stimulus is the ---- reaching the rods and cones of the eye. Because processing of that stimulus by the brain is a psychological phenomenon, the perception of color varies between ----. In addition, the color of an object depends on the --- in which the object is viewed.

Back 59

light, individuals, light

Front 60

What are the types of systems are used to measure color?

Back 60

Munsell color system

The other system involves measurement of color with a spectrophotometer or a colorimeter

Front 61

The ---- involves matching the test object to color tabs resembling those available in a paint store. Each tab has ---, ----, and ---- numbers assigned.

Back 61

Munsell color system, hue, chroma, values

Front 62

the fundamental color of an object, as in red, green, or blue.

Back 62

Hue

Front 63

the strength or color saturation of the hue, as in pink versus red.

Back 63

Chroma

Front 64

the light or darkness of the color, as in shades of gray.

Back 64

Value

Front 65

In dentistry, esthetic mate-rials have their own set of color tabs or shades, called a ---. Some manufacturers use a standard set, such as the --- shade guide. Recently, handheld devices have been developed that measure the color of teeth through a ---. These devices provide maps of the various shades of a tooth.

Back 65

shade guide, Vita, digital camera

Front 66

measures the intensity of light that is reected by an object at numerous wavelengths of visible light.

Back 66

spectrophotometer

Front 67

measures light at several wavelengths, much like the human eye.

Back 67

colorimeter

Front 68

For both the spectrophotometer and colorimeter, the data are mathematically manipulated by a computer to reduce the information to three numbers: ---, ---, and ---.

Back 68

L*, a*, b*.

Front 69

The number L* is very similar to ---. The number a* is a measure of the --- character of a color. The number b* is a measure of the --- character of a color.

Back 69

value,red–green, blue–yellow

Front 70

The interaction of teeth and dental materials with ultraviolet light causes ---- and affects their appearance. Fluorescence of restorations is important when fluorescent lighting or “black” lights are present. Inadequate fluorescence will make a crown or a lling appear --- in certain lighting, but excess fluorescence will make a tooth ---- in the same lighting.

Back 70

fluorescence, dark, “glow”

Front 71

Some materials are radiolucent and are not seen on radiographs. Examples are some ---materials and denture ----. Other materials, such as ----, are radiopaque and are evident on radiographs. Some dental restorative materials have been formulated by the manufacturer to match the radiopacity of enamel to facilitate the diagnosis of -----.

Back 71

ceramic, acrylic resin, metal restorations, recurrent decay

Front 72

Because teeth are used to --- and ---- food, they must be ---, and so must the materials that are used to replace missing tooth structure.

Back 72

tear, grind, strong

Front 73

When we bite on a tooth, an --- force (biting) is placed on the tooth. A force is a --- or ---- applied to an object. Inside the tooth, an ---- stress develops to resist the applied external force. This stress is the force divided by the area on which the force has been applied. The internal stress that develops in the tooth is ---- to the external force applied; however, they are ----in direction.

Back 73

external, weight, load, internal, equal, opposite

Front 74

Teeth are composed of strong materials with strong ----. Teeth and their atomic bonds are stronger than the stresses that develop as a result of ----. On the other hand, food cannot resist these forces and breaks because the strength of the ---- atomic bonds of the food morsel is exceeded.

Back 74

atomic bonds, biting, weak

Front 75

The atomic bonds of teeth can be thought of as micro-scopic springs. These springs are --- each time we bite. When we relax our bite and our teeth are no longer in contact, the springs return to their --- length.

Back 75

compressed, original

Front 76

change in shape and return to the original shape

Back 76

elasticity

Front 77

---- is the change in length divided by the origi-nal length. Strain is measured as a fraction (such as 0.02) or as a percentage (such as 2%). The longer the object is, the more it must be ---- to have the same strain

Back 77

Strain, stretched

Front 78

the force that develops in a loaded object is called ----, and stress is --- to the applied force or load. Stress is also related to the --- of the object. The change in --- or strain remains constant, as does the stress. When a load or a force is applied to an object, the stress occurs throughout the object’s entire length.

Back 78

stress, proportional, size, length

Front 79

The load (stress) and the change in length (strain) are ---. If the load is small, the change in length may be difficult to measure.

Back 79

proportional

Front 80

The proportionality constant, or the slope of a graph of stress versus strain.

Back 80

modulus of elasticity

Front 81

The higher the modulus of elasticity is, the --- the material. Enamel has a --- modulus of elasticity.

Back 81

stiffer, high

Front 82

When a stress is removed and the object returns to its original length, the initial change in length is called ----.

Back 82

elastic deformation

Front 83

If we take all the charms off the spring, the spring does not return to its original length. It has become permanently stretched out. This condition is termed ---- or ----

Back 83

plastic deformation or permanent deformation.

Front 84

The point on the stress–strain plot at which the line starts to curve and plastic deformation begins is called either the ----, ---- or ----,

Back 84

elastic limit, the proportional limit, or the yield point

Front 85

If we could keep loading on more and more charms, at some point the spring breaks (or fail-ure occurs). We have exceeded the strength of the spring. The stress at that point is called the ----.

Back 85

ultimate strength

Front 86

Types of Stress

Back 86

Compression

Tension

Shear

Torsion

Bending

Front 87

a pushing or crushing stress.

Back 87

Compression

Front 88

a pulling stress.

Back 88

Tension

Front 89

(slip) stress occurs when parts of an object slide by one another.

Back 89

Shear

Front 90

a twisting force.

Back 90

Torsion

Front 91

a common stress and is actually a combination of several types of stresses

Back 91

Bending

Front 92

When an object is bent, one side is ---, but the opposite side is ----. In addition to these compressive and tensile forces, --- forces also occur inside the object.

Back 92

compressed, stretched, shear

Front 93

In restorative dentistry, the materials that we use for fillings and crowns need to be --- and ---. The materials that we use for taking impres-sions are much --- stiff than restorative materials. Some impression materials are quite --- and stretch a great deal.

Back 93

stiff, strong, less, flexible

Front 94

To function properly, a restoration must be hard (hardness), strong (yield strength), and stiff (modu-lus) enough to withstand the forces of ---. For many uses of materials, the --- strength is more important than the --- strength.

Back 94

mastication, yield, ultimate

Front 95

If a gold crown yields or plastically deforms (changes shape) when one bites down, it is no longer the same shape and is not likely to fit the tooth preparation precisely. ---- is then likely. Thus, we are much more concerned with the ---of a restoration in service (not exceeding the yield strength) than we are with a restoration breaking (ultimate strength).

Back 95

Recurrent caries, fit?

Front 96

Elastic deformation occurs whenever force is applied to an object. As the force increases, ---- may occur.

Back 96

plastic deformation

Front 97

Impressions should return to their original shape after they have been ---- from the mouth. If not, the resulting stone cast will not be the same--- as the teeth or cavity preparation.

Back 97

removed, size

Front 98

a mechanical property that is the ratio of the strain in the direction of the stress to the strain in a direction perpendicular to the stress.

Back 98

Poisson’s ratio

Front 99

measured as the area under the stress–strain curve up to the yield point.

Back 99

Resilience

Front 100

a measure of the energy required to fracture a material when a crack is present.

Back 100

Fracture toughness

Front 101

Many things fail after being stressed repetitively for a long time, and such failure is called ----

Back 101

fatigue

Front 102

the small change in shape that results when an object is under continuous compression.

Back 102

Creep

Front 103

---- is similar to creep. Both occur slowly, over time. Creep is a slow change in shape, but stress relaxation is a slow decrease in force over time.

Back 103

Stress relaxation

Front 104

Stress increases around defects. This phenomenon is called ----.

Back 104

stress concentration

Front 105

A drop of water on a Popsicle is an example of:

Back 105

Good wetting (low contact angle) indicates that the adhesive is in very close contact with the adherend, forming a low con-tact angle. Poor wetting “stays as a drop,” and a high contact angle is formed.

Front 106

The tightening of a guitar string is an example of which of the following stresses?

Back 106

Tension is a pulling or stretching stress, which many times is referred to as tensile stress. Compression is a crushing or pushing force. Torsion is a twisting stress, and shear is a sliding stress.

Front 107

The modulus of elasticity is an indication of what property of a material?

Back 107

Stiffness

The higher the modulus of elasticity, the stiffer is the material. The modulus is a measure of exibility. A rub-ber band has a low modulus; a mouth mirror has a high modulus. Resilience is the ability of a material to absorb energy without deforming, whereas toughness is the ability of a material to absorb energy up to and includ-ing failure or fracture.

Front 108

Cooled materials will contract, and heated materials will expand. A measurement of this change in volume in rela-tion to change in temperature is called the coefcient of thermal expansion.

Back 108

Both statements are true.

Nearly all materials will contract (sometimes ever so slightly) when cooled and expand when heated. Measuring this change in size (volume) in relation to the change in temperature is called the coefcient of thermal expansion. In dentistry, this property holds importance because, ideally, the tooth structure and the restorative material should expand and contract by the same amount.

Front 109

When a stress is induced in a material that is greater than the material’s yield strength, the stress is ----- pro-portional to the strain, and the material does not return to its original shape.

Back 109

No longer

Remember that you cannot have stress (load) without strain (change in length). They occur together. When they are proportional, as illustrated on a graph, it is a straight line. As we increase the load (by adding more monkey charms), eventually, the spring will not go back to the original length. This stress is no longer propor-tional to the strain. We have reached the yield strength on the graph, and the line begins to curve.

Front 110

An example of a physical property is:

Back 110

Density

Other examples of physical properties are color and thermal conductivity. Strength and stiffness are mechanical properties, and setting reactions are chemi-cal properties.

Front 111

A twisting force is termed:

Back 111

Torsion is a twisting stress, such as turning a door-knob. Shear stress occurs when parts of an object slide past each other. Tension is a pulling stress, and bending is a combination of compression, tension, and shear stresses.

Front 112

The ability of a material to dissolve in liquid is termed:

Back 112

Solubility is calculated as the amount of material that dissolves in a given time. Viscosity is the ability of a material to ow. Water sorption is the ability of a material to absorb water. Wetting is the interaction of a liquid with a surface.

Front 113

Elasticity is an example of which property?

Back 113

Mechanical properties include stress, strain, resil-ience, toughness, fatigue, and elasticity, to name a few. Physical properties include thermal conductiv-ity, heat capacity, vapor pressure, viscosity, hardness, and many more. Chemical properties describe set-ting reactions and decay and degradation. Biologic properties are the effects materials have on living tissue.

Front 114

The rate of heat flow through a material is referred to as

Back 114

Thermal conductivity is the rate of heat flow through a material. It is measured as heat ow over time. Heat capacity is a measure of the amount of thermal energy a material can hoard (like a micro-wave trivet), whereas heat of fusion is the amount of energy required to melt a material. The coefcient of thermal expansion is a measure of change in volume in relation to the temperature change.

Front 115

Jennifer is a practicing hygienist who goes to a nearby restaurant each day for lunch. She often orders a cola with ice and a bowl of homemade soup. As she eats and drinks, her composite restorations (tooth colored) and tooth struc-ture are expanding and contracting at different rates. This change in volume or length of these materials due to the hot food and cold drink is referred to as:

Back 115

Coefficient of thermal expansion

The composite resin restor-ative material expands and contracts at a different rate than enamel and dentin. Over time, a gap is created between the tooth and restoration when it contracts (from cold beverage) and then closes when the soup is eaten. This process is called percolation and may result in microleakage, tooth sensitivity, and recurrent decay.

Front 116

Fingernail polish remover has “solvent” properties, as it will remove the polish from our ngernails. Another prop-erty polish remover has is its tendency to evaporate. Fin-gernail polish remover can be said to have:

Back 116

A high vapor pressure

Those liquids that act as solvents and evaporate readily have a high vapor pressure. Materials with low vapor pressure do not evaporate quickly. All liquids have some degree of vapor pressure. A liq-uid’s vapor pressure is a constant, and does not vary. Therefore, it cannot be “intermittent.”

Front 117

------ is the force used to condense an amalgam in a preparation.

Back 117

Compression is dened as “a pushing or crushing stress.” The pressing of the plastic mass of amalgam by the amalgam condenser instrument is an example of compression.

Front 118

A hardened cement having “low” ----- can firmly hold a patient’s gold crown in place for years in a wet envi-ronment.

Back 118

Solubility is a measure of a materials’ ability to dis-solve in water. The dental cement has a low solubility and serves the patient well by not dissolving for a long period of time in the patient’s mouth. Cements have the most demanding requirements of any material.

Front 119

----- is the term given to the increase of stress around defects within an object.

Back 119

Stress concentration occurs near voids, pits, and cracks. Stress concentration may cause breaks and fractures at a much lower stress than if they were not present.