Physical properties
Based on laws of physics that describe mass, energy, force, light, heat, electricity, and other physical phenomena. Ex. color, density, and thermal conductivity.
Mechanical properties
Describes a material's ability to resist forces. Dependent on the amount of material and on the size and shape of the object. Ex. strength and stiffness
Chemical properties
Setting reactions as well as the decay or degradation of materials. Ex. gypsum products set via a precipitation process, whereas dental composites polymerize.
Biologic properties
Effects the materials have on living tissue. Ex. crown should not irritate the gingiva, tongue, or buccal mucosa.
Density
Mass of a material in a given volume.
Common unit gm/cm3
As the atomic # increases so do the density
Depends on the packing together of atoms and molecules
Depends on the voids in the material
High density makes metals feel heavy
Boiling and Melting points
Can be used to help identify chemicals
Mixtures usually have a range rather than a specific point.
When an object melts, atomic bonds between the atoms or molecules are broken by the thermal energy of the material.
Some metals melt at very high temps and
Vapor pressure
Measure of a liquid's tendency to evaporate and become gas.
As temp increases, the vapor pressure also increases.
Copal Varnish / Dentinal Adhesive - Mixture is applied, and the solvent evaporates, leaving behind a thin film of the desired substance.
Low
Thermal conductivity
Rate of heat thru a material
Measured in calories/second-meter-degree
Depends on the distance the heat travels, the area in which the heat travels, and the difference in temp between the source and destination.
Insulating base in placed beneath metal rest
Heat capacity
A measure of the amount of the thermal energy that a material can hoard. Some material require more energy than others to heat
Specific heat
The amount of energy need to raise the temperature of one unity of mass of that material by 1 Celsius.
Measured in calories/gram-degree
Heat capacity of water is 1 calories/gram-degree
Heat of fusion
Amount of energy required to melt a material.
The high heat of fusion allows a small amount of ice to effectively cool a much larger amount of beverage without excessive dilution as it melts.
Heat of vaporization
Amount of energy required to boil a material.
Coefficient of thermal expansion
Fractional change in volume or length.
Materials usually shrink when cooled and expand when heated.
Percolation
When a restorative material and the coefficient of thermal expansion of a tooth is mismatched, the restoration will shrink with cold beverages, opening gaps between the restoration and the tooth. When the tooth heats again and expands, the gap is closed.
Electrical conductivity
Metals are good conductors.
Polymers and ceramic are poor conductors and are insulators.
often corrosive
Galvanic shock
Result of electricity flowing from the fork to the amalgam and through the pulp.
Viscosity
A material ability to flow
Viscous or thick liquids flow poorly
Thin liquid flow easily
Has temp-dependent property
Measured as grams/meter-second or Poise (P)
Low viscosity and the ability to wet a surface is important
Wetting
Brings the material into intimate associate with the surface so that chemical and micromechanical bonding can occur.
Measured by determining the contact angle of a liquid on a solid.
Low contact angle
Good wetting; drop of water on a piece of ice.
When gypsum plaster is poured into an impression, the fine details of the impression will be reproduced in the cast
High contact angle
Poor wetting, drop of water on a piece of plastic
When gypsum plaster is poured into an impression, bubbles will likely result in insufficient detail and an unusable cast.
Hardness
Resist scratching and indenting by soft materials.
Measured by scientific instruments that press a special tip into the surface of the test material and the indentation is measured.
Hardness is calculated based on the size of the indentation.
Knoop hardne
Durometer measurement
Measures how deep a steel ball will sink when pressed into the surface of a material.
Used to measure the hardness of impression material and other elastic polymers.
Abrasive resistance
Wear resistance; of dental restorations to food and opposing teeth.
Harder materials are more resistant to abrasion than softer materials.
The wear of enamel opposing dental restorations.
A restoration must be hard enough so that the restoration does not
Goldilocks principle
Not too hard, not too soft, just right
Solubility
The amount of a material that dissolves in a liquid, such as water.
The weight of the material dissolved into the water is the solubility of that material.
Excessive solubility leads to loss of material and increases the risk of recurrent decay
Water sorption
Materials that absorb water.
Immerse test sample is water and the weight that is gained by that sample is the water sorption.
Cookie dunked in milk
Color
Psychological response to a physical stimulus
Physical stimulus is the light reaching the rods and cones of the eye and the processing of the stimulus by the brain is a psychological phenomenon.
Location of the restoration.
The shape and health of the gin
Interaction of Materials w X-Rays
Ceramic materials and denture acrylic resin are radiolucent and are not seen on radiographs.
Metal restorations are radiopaque and are evident on radiographs.
What happens to a tooth or restoration when we bite on it?
A external force (biting) is placed on the tooth.
Force
A weight or LOAD applied to an object.
Internal stress
Inside the tooth, an internal stress develops to resist the applied external force.
Stress
The force that develops in a loaded object and is proportional to the applied force or load.
Also related to the size of the object.
The force divided by the area on which the force has been applied.
The internet stress that develops in the tooth is equal
Why don't teeth break when we use them to grind our food?
Teeth are composed of strong material and strong atomic bonds. Teeth are stronger then the stresses that develop as a result of biting. Food cannot resist these forces (biting) and breaks because the strength of the weak atomic bonds of the food morsel is
Elasticity
Atomic bonds of teeth can be thought of as microscopic springs.
These springs are compressed each time we bite.
Atomic bonds that are stretched return to their original length.
When an object is bent, the same stretching of atomic bonds occurs in some par
Strain
The change in length divided by the original length.
The longer the object is, the more it must be stretched to have the same strain.
Relationship of Stress and Strain
The load (stress) and the change in length (strain) are proportional and there can't be one without the other.
Modulus of elasticity
The slope of a graph of stress versus strain
Scientific term for the stiffness of a material
The higher the modulus of elasticity, the stiffer the material. (Enamel)
Low modulus - rubber
Elastic deformation
The initial change in length, when stress is removed and the object returns to its original length.
Plastic deformation / Permanent deformation
When the line on the graph begins to curve, which means stress is not longer proportional to strain.
It has permanently stretched out.
Occurs when an orthodontic wire is bent to fit a patient's arch.
Force placed on the wire and it bents
Elastic limit / Proportional limit / Yield point
The point on the stress-strain plot at which the line starts to curve and plastic deformation begins.
Ultimate strength
When the spring breaks or failure occurs.
We have exceeded the strength of the spring.
Ultimate tensile strength
If the test is a tensile (tension) test
Ultimate compressive strength
If the test is a compressive test