Phillips science of dental materials

Question 1

According to Phillips science of dental materials, which of these materials displays the best wetting, which displays the worst?

Answer 1

Clean glass is best, angle approaches 0

Teflon is worst, angle is >90 degrees

Question 2

According to Phillips Science of dental materials,

What is depicted in this graph by points

A (no plastic deformation has occurred),

B (0.2% plastic deformation has occurred),

C (Material fractured),

D (slope of this portion of the line?

Answer 2

A - proportional limit

B - Yield strength (0.2%)

C - Ultimate strength

D - Elastic modulus

Question 3

According to Phillips Science of dental materials,

These are stress strain curves for 3 materials undergoing tensile stress.

What do letters A-F represent?

Answer 3

A, C, E (and F) Represent the ultimate tensile strength (stress required to fracture) of materials A, B and C

B, D, and F (also E since E=F) represent the proportional limit - end of the linear part of the stress/strain curve or amount of stress a material can withstand before plastic deformation occurs.

Question 4

According to Phillips Science of dental materials,

These are stress strain curves for 3 materials undergoing tensile stress.

What material has the highest modulus of elasticity?

Answer 4

Material A - steepest straight portion of stress strain curve

Question 5

According to Phillips Science of dental materials,

These are stress strain curves for 3 materials undergoing tensile stress.

What do letters G, H and I represent?

Answer 5

The ductility of materials C, B, and A respectively.

This is the percent elongation in the plastic phase of deformation.

A is most ductile

Question 6

According to Phillips Science of dental materials,

These are stress strain curves for 3 materials undergoing tensile stress.

Which material is most brittle? Which is least?

Answer 6

Most brittle is C - has no plastic phase of deformation, breaks before any plastic deformation occurs

Least brittle is A - has the longest plastic phase of deformation.

Question 8

According to Phillips science of dental materials,

What Contact angle indicates no wetting

Answer 8

180

Question 9

According to Phillips science of dental materials,

what contact angle indicates complete wetting?

Answer 9

0

Question 10

According to Phillips science of dental materials,

What is the difference between adhesion and cohesion?

Answer 10

adhesion is the sticking of a substance to something different, cohesion is how well atoms/molecules stick to other atoms/molecules that are the same

Question 11

According to Phillips science of dental materials,

What is wetting?

Answer 11

The ability of a liquid to maintain contact with a solid surface; it reflects the intermolecular interactions when the two are brought in intimate contact.

Question 12

According to Phillips science of dental materials,

What is a thixotropic material?

Answer 12

Property of gels and other fluids to become less viscous and flow when subjected to steady shear forces through being shaken, stirred, squeezed, patted, or vibrated. When the shear force is decreased to zero, the viscosity increases to the original value. Also known as shear thinning, in which the greater the applied shear force, the less the resistance to flow

Question 13

According to Phillips science of dental materials,

What is creep?

Answer 13

Time-dependent plastic strain of a solid under a static load or constant stress.

Question 14

According to Phillips science of dental materials,

What is the coefficient of thermal expansion>?

Answer 14

AKA (linear coefficient of expansion)—Change in length per unit of the original length of a material when its temperature is raised by 1 K (1 °C).

Question 15

According to Phillips science of dental materials,

What is corrosion?

Answer 15

Chemical or electrochemical process in which a solid, usually a metal, is attacked by an environmental agent, resulting in partial or complete dissolution

Question 16

According to Phillips science of dental materials,

What is brittleness?

Answer 16

Relative inability of a material to deform plastically before it fractures.

Question 17

According to Phillips science of dental materials,

What is Compressive stress

Answer 17

Compressive force per unit area perpendicular to the direction of applied force.

Question 18

According to Phillips science of dental materials,

What is Compressive strength

Answer 18

Compressive stress at fracture.

Question 19

According to Phillips science of dental materials,

What is Ductility?

Answer 19

Relative ability of a material to elongate plastically under a tensile stress. This property is reported quantitatively as percent elongation.

Question 20

According to Phillips science of dental materials,

What is Elastic strain?

Answer 20

Amount of deformation that is recovered instantaneously when an externally applied force or pressure is reduced or eliminated.

Question 21

According to Phillips science of dental materials,

What is Elastic modulus?

Answer 21

(also modulus of elasticity and Young’s modulus)—Stiffness of a material that is calculated as the ratio of elastic stress to elastic strain.

Question 22

According to Phillips science of dental materials,

What is Flexural strength?

Answer 22

(bending strength or modulus of rupture)—Force per unit area at the instant of fracture in a test specimen subjected to flexural loading.

Question 23

According to Phillips science of dental materials,

What is Flexural stress?

Answer 23

bending stress —Force per unit area of a material that is subjected to flexural loading.

Question 24

According to Phillips science of dental materials,

What is Hardness?

Answer 24

Resistance of a material to plastic deformation, which is typically produced by an indentation force

Question 25

# According to Phillips science of dental materials, What is Plastic strain?

Answer 25

Irreversible deformation that remains when the externally applied force is reduced or eliminated.

Question 26

# According to Phillips science of dental materials, What is pressure? What is stress?

Answer 26

Pressure—Force per unit area acting on the surface of a material Stress—Force per unit area within a structure subjected to a force or pressure

Question 27

# According to Phillips science of dental materials, What is the proportional limit?

Answer 27

Magnitude of elastic stress above which plastic deformation occurs.

Question 28

# According to Phillips science of dental materials, What is resilience?

Answer 28

The amount of elastic energy per unit volume that is sustained on loading and released upon unloading of a test specimen.

Question 29

# According to Phillips science of dental materials, What is shear stress?

Answer 29

Ratio of shear force to the original cross-sectional area parallel to the direction of the applied force.

Question 30

# According to Phillips science of dental materials, What is shear strength?

Answer 30

Shear stress at the point of fracture

Question 31

# According to Phillips science of dental materials, What is stress?

Answer 31

Force per unit area within a structure subjected to a force or pressure

Question 32

# According to Phillips science of dental materials, What is Strain?

Answer 32

Change in dimension per unit initial dimension. For tensile and compressive strain, a change in length is measured relative to the initial reference length.

Question 33

# According to Phillips science of dental materials, What is Stress concentration?

Answer 33

Area or point of significantly higher stress that occurs because of a structural discontinuity such as a crack or pore or a marked change in dimension.

Question 34

# According to Phillips science of dental materials, What is ultimate strength?

Answer 34

stress at the point of fracture (ultimate strength).

Question 35

# According to Phillips science of dental materials, What is tensile stress?

Answer 35

Ratio of tensile force to the original cross-sectional area perpendicular to the direction of applied force.

Question 36

# According to Phillips science of dental materials, What is tensile strength?

Answer 36

Tensile stress at the instant of fracture.

Question 37

# According to Phillips science of dental materials, What is Toughness?

Answer 37

Ability of a material to absorb elastic energy and to deform plastically before fracturing; measured as the total area under a plot of tensile stress versus strain.

Question 38

# According to Phillips science of dental materials, What is yield strength?

Answer 38

The stress at which a test specimen exhibits a specific amount of plastic strain.

Question 39

# According to Phillips science of dental materials, What happens to a material when stress is applied to a material that is below the proportional limit, and the stress is removed?

Answer 39

It will return to original shape as below the proportional limit only elastic deformation occurs

Question 40

# According to Phillips science of dental materials, What happens to a material when stress is applied to a material that is beyond the proportional limit, and the stress is removed?

Answer 40

It will not return to it's original form as some plastic deformation will have occurred.