A subgroup of physical properties; describe a material's ability to resist forces
Mechanical Properties
Examples of Mechanical Properties
Strength and stiffness
Describes the setting reactions as well as the decay or degradation of materials.
Chemical properties
Examples of Chemical Properties
Gypsum products set by a precipitation process, whereas dental composites polymerize
The effects the materials have on living tissue
Biologic properties
Examples of Biologic Properties
A crown should not irrigate the gingiva, tongue, or buccal mucosa
Types of Physical Properties
Density
Boiling and Melting Points
Vapor Pressure
Thermal Conductivity
Heat Capacity
Heat of Fusion and Vaporization
Coefficient of Thermal Expansion
Electrical Conductivity
Viscosity
Hardness
Durometer measurements
Abrasion Resistance
Solubility
Water So
The amount of mass of a material in a given volume
Density
Common Unit of density
g/cm^3
3 Things that Density depends on:
1. The type of atoms present
2. The packing together of atoms and molecules
3. The voids in the material
What happens when an object melts or boils?
The atomic bonds between the atoms or molecules are broken by the thermal energy of the material.
A measure of a liquid's tendency to evaporate and become a gas.
Vapor Pressure
The rate of heat flow through a material.
Thermal Conductivity
Measurement of thermal conductivity depends on:
1. The distance the heat travels
2. The area in which the heat travels
3. The difference in temperature between the source and destination
A measure of the amount of thermal energy that a material can hoard.
Heat Capacity
The amount of energy needed to raise the temperature of one unit of mass of that material by 1 degree Celsius.
Specific Heat Capacity
The amount of energy required to melt a material.
Heat of fusion
The amount of energy required to boil a material.
Heat of vaporization
A measure of this change in volume in relation to the change in temperature
Coefficient of Thermal Expansion
The process of heating and cooling, and the accompanying opening and closing of the gap
Percolation
Results of percolation
Microleakage
Tooth Sensitivity
Recurrent Decay
The result of electricity flowing from the fork to the amalgam and through the pulp.
Galvanic Shock
Ability to flow
Viscosity
Brings the material into intimate association with the surface so that chemical and micromechanical bonding can occur.
Wetting
High Contact Angle
Poor wetting ( a drop of water on plastics)
Low Contact Angle
Good wetting ( a drop of water on a piece of ice)
A property that is measured by scientific instruments that press a special tip into the surface of the test material
.hardness
hardest biological tissue in the human body
Enamel
Knoop hardness number (KHN) of enamel
350
Knoop hardness number (KHN) of dentin
70
Knoop hardness number (KHN) of porcelain
400 to 500
Knoop hardness number (KHN) of acrylic denture teeth
20
Used to measure the hardness of impression materials and other elastic polymers
Durometer
Wear resistance of dental restorations to food, opposing teeth, and other dental materials.
Abrasion Resistance
Not too hard; not too soft; just right, when referring to dental materials
Goldilocks Principle
The amount of a material that dissolves in a liquid, such as water.
Solubility
Materials ability to absorb water.
Water soprtion
Matching the test object to color tabs
Munsell Color System
A set of color tabs or shades for esthetic materials in dentistry
Shade Guide
Measures the intensity of the light that is reflected by an object at numerous wavelengths of visible light.
Spectrophotometer
Measures light at several wavelengths, much like the human eye.
Colorimeter
Types of Mechanical Properties
Elasticity
Strain
Stress
Poisson's Ratio
Resilience and Toughness
Fracture toughness
Fatigue
A weight or load applied to an object; a measure of push or pull
Force
The force divided by the area on which the force has been applied; The force that develops in a loaded object
Stress
Change in shape and return to the original shape
Elasticity
The change in length divided by the original length
Strain
What is the relationship of stress and strain?
the load (stress) and the change in length (strain) are proportional and always occur together.
The proportionality constant, or the slope of a graph of stress versus strain.
Modulus of Elasticity
When a stress is removed and the object returns to its original length
Elastic Deformation
When a stress is removed and the object does not return to its original length
Plastic deformation/Permanent deformation
The point on the stress-strain plot at which the line starts to curve and plastic deformation begins
Elastic limit/ Proportional Limit/ yield point
When the object breaks because of all the stress and strain
Ultimate Strength
Types of Stress
Compression
Tension
Shear
Torsion
Bending
A pushing or crushing stress
Compression
A pulling stress
Tension
Occurs when parts of an object slide by one another.
Shear
A twisting force
Torsion
A common stress and is a combination of several different kinds of stresses.
Bending
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.
Poisson's Ratio
An ability to absorb energy and not become deformed
Resilience
Ability to absorb energy while distorting or fracturing
Toughness
A measure of the energy required to fracture a material when a crack is present.
Fracture Toughness
Failure of objects after being stressed repeatedly for a long time
Fatigue
Time-Dependent properties
Creep
Stress Relaxation
the small change in shape that results when an object is under continuous compression. (Very slow flow)
Creep
Slow decrease in force over time. (the loss of pull of a rubber band that has been stretched out for a long period of time)
Stress Relaxation
Stress increases around defects (cracks developing around a defect and spreading throughout the object)
Stress Concentration
A drop of water on a popsicle is an example of:
Good wetting (low contact angle)
the tightening of a guitar string is an example of which stress?
Tension (pulling stress)
The modulus of elasticity is an indication of what property of a material?
Stiffness
T or F: Cooled materials will contract, and heated materials will expand. A measurement of this change in volume in relation to change in temperature is called the coefficient of thermal expansion.
Both statements are true
When a stress is induced in a material that is greater than the material's yield strength, the stress is ___ proportional to the strain, and the material does not return to its original shape.
No longer
Which formula defines the modulus of elasticity?
stress/strain
Elasticity is an example of which property?
Mechanical
The rate of heat flow through a material is referred to as:
Thermal Conductivity
Composite restorations and tooth structures expanding at different rates because of hot and cold contact is referred to as:
Coefficient of thermal expansion
The force used to condense an amalgam in a preparation
Compression
A hardened cement having a low ______ can firmly hold a patient's gold crown in place for years in a wet environment.
Solubility
____ is the term given to the increase of stress around defects within an object.
Stress Concentration
Based on the laws of physics that describe mass, energy, force, light, heat, electricity, and other physical phenomena.
Physical Properties
Examples of Physical Properties
Color, density, and thermal conductivity