Material Properties Flashcards
What are the 4 categories of Material properties?
Physical
Mechanical
Chemical
Biologic
Physical properties refer to 5 areas of interest which are:
1
2
3
4
5
1 mass properties
2 thermal properties
3 electrical properties
4 optical properties
5 surface properties
Mechanical properties refer to:
a description of the stresses and strains within a material resulting from an external force.
Chemical properties refer to:
chemical and electrochemical interactions
Biologic properties refer to:
characterization of toxicity or sensitivity reactions.
Materials respond to environment according to their _____________ and _________________
Materials respond to the environment according to their structure and bonding
due to the coefficient of Thermal Expansion what happens during temperature increases or decreases.
When temperature increases atomic motion increases which stretches bonds and produces expansion. The opposite is true when temperatures are decreased (ie: shrinkage, *think george castanza* “I was in the pool!”)
Which materials have low coefficient of thermal expansion and which materials have high coefficient of thermal expansion?
ceramics
metals
polymers
tooth structure
LOW (dont expand much)
• Ceramics: 1-15 ppm/°C
Tooth Structure: 9-11 ppm/°C
Metals: 10-30 ppm/°C
Polymers: 30-600 ppm/°C
HIGH (expand quite a bit)
What is Percolation?
Percolation is where the margins of a restoration become weaker and “leaky” because the restoration undergoes cyclical expansion and contraction at a different rate than the tooth structure around it.
Major cause of loosening restorations and secondary caries
This is an example of PERCOLATION! note the expansion and contraction as temperature changes. This weakens the margins and can result in secondary caries.
What is thermal conductivity?
thermal conductivity is the ability of a material to conduct heat.
Low conductors are also good insulators
What are some examples of materials that are good insulators/poor conductors?
Dentin, Cements, composite resins, cavity liners
High conductivity means the material is a poor insulator and will conduct heat readily. What are some examples of materials that are good conductors/poor insulators?
amalgam and gold
What is HEAT DIFFUSIVITY?
Heat diffusivity is a measurement of heat conductivity per unit time, it takes the density of the material into account.
Dental pulp can withstand __________ temperature changes for __________amounts of time with ___________ damage
dental pulp can withstand small temperature changes (37-42 °C) for short periods of time (30-60 seconds) with no permanent damage.
What is Electrical Conductivity
rate of electron transport through a material
What types of materials are best at conducting electricity?
Metallic restorations may conduct flow through the pulp.
Amalgam + gold = shock
What does specific gravity refer to?
specific gravity refers to the density of a material in reference to water
What are the 4 main categories or Optical Properties
Reflection- light bounces off surface
Refraction- light is bent as it passes through (changes directions at surface)
Absorption (and Fluorescence)- light loses energy as it goes through
Transmission- linked to opacity/translucency
What are the 3 categories in the MUNSELL COLOR SYSTEM
HUE (wavelength)
VALUE (intensity)
CHROMA (purity)
In dentistry we use a __________ to help us match restorative dental materials to tooth structure.
A SHADE GUIDE
What 3 substances are added to composite materials to make them radiopaque on radiographs?
Lithium
Barium
Strontium
What does Contact Angle refer to?
The angle a drop of liquid makes with the surface it is resting upon.
What determines if a material is “Poor/Non Wetting”?
Contact Angle greater than 90 degrees and or/ approaching 180 degrees
