Chapter 3: Physical, Chemical, Mechanical Properties, and Biocompatibility of Dental Materials Flashcards
Chemical Properties and Parameters
- Corrosion
- Hygroscopy
- Solubility
- pH sensitivity
- Reactivity
- Surface energy
- Surface tension
Properties of Importance in Manufacturing or Finishing Processes
- Castability
- Brittleness
- Creep resistance
- Hardness
- Melting temperature or melting temperature range
- Flowability under hot-isostatic pressing (HIP) temperature and pressure conditions
- Machinability
- Polishability
Mechanical Properties
- Brittleness
- Compressive strength
- Ductility
- Elastic modulus
- Fatigue strength
- Fracture toughness
- Hardness
- Microtensile strength
- Polsson’s ratio
- Proportional limit
- Shear strength
- Tensile strength
- Work or stain hardening
- Yield strength
Optical Properties and Parameters
- Absorptivity
- Color
- Fluorescence
- Luminescence
- Opacity
- Photosensitivity
- Reflectivity
- Refractive index
- Translucency
- Transmittance
Thermal Properties and Parameters
- Coefficient of thermal expansion or contraction
- Eutectic temperature
- Fusion temperature
- Glass transition temperature
- Heat of vaporization
- Heat of fusion
- Liquidus temperature
- Melting point
- Softening point
- Solidus temperature
- Specific heat
- Thermal conductivity
- Thermal diffusivity
- Vapor pressure
- Viscosity
Properties based on the laws of mechanics, acoustics, optics, thermodynamics, electricity, magnetism, radiation, atomic structure or nuclear phenomenon.
Physical Properties
This is defined as the study of the deformation and flow characteristic of matter whether liquid or solid
Rheology
The property of fluid that causes it to resist flowing; it is a measure of the consistency of a fluid and its inability to flow.
Viscosity
Example of material that transforms from fluid to solid in the mouth.
Cements & Impression Materials
These products transforms extraorally from fluid slurries into solids.
Gypsum Products
These products appear solid but are actually supercooled liquids that flow plastically (irreversible) or elastically (reversible) under small stresses.
Amorphous Materials (waxes and resins)
Which is more viscous, glass ionomer or zinc phosphate cements?
Glass Ionomer
TRUE OR FALSE: Light-body polysulfide is more viscous than heavy-body polysulfide at 36°C.
FALSE
Light-body polysulfide is less viscous than heavy-body polysulfide at 36°C.
A liquid that becomes less viscous with increase in temperature and becomes more fluid under pressure.
Thixotropic Liquid
Examples of Thixotropic Liquids
Dental Prophylaxis Pastes
Plaster
Resin Cements
Some Impression Materials
A relief of stress after permanent deformation of a substance through a solid-state diffusion process driven by thermal energy cause distortion and warping.
Structural and Stress Relaxation
INFO: Elastomeric impression materials undergo stress relaxation and are therefore prone to distortion leading to lack of it.
INFO: The rate of relaxation increases with an increase in temperature.
Non-crystalline dental materials such as waxes, resins, and gels when manipulated and cooled, can undergo relaxation at an elevated temperature.
Color exist only if three conditions are satisfied:
- An object or “modifier” - that interacts with the light source.
- Light source.
- An observer or recipient of the modified light coming from the object.
What are the different color measuring systems?
- Munsell Coloring System
- CIE (Commission Internationale de I’Eclairage)
A visual system based on a well-defined series of color tabs, that are precisely arranged. Composed of three indices: Hue, Value, and Chroma.
Munsell Coloring System
A spectrophotometric system that uses an expensive equipment to define how much red, blue, and yellow a certain object appears to contain.
CIE (Commission Internationale de I’Eclairage)
What are the three dimensions of colors?
- Hue
- Value
- Chroma
Refers to the dominant color of the object
Hue
Natural teeth do not vary much in terms of their hue, generally being in the ________ to ________ range.
yellow to yellow-red
This dimension of color is also called “Gray-scaled”. It refers to the lightness or darkness of a color.
Value
On a scale from 1 to 10, with 1 = black (low value) and 10 = white (high value), what is the value of natural teeth?
Natural teeth are generally high in value, in the range of 6-8 for most people.
INFO: The spectral distribution of light reflected or transmitted through an object is dependent on the spectral content of the incident light.
The difference in color perception under different light sources.
Metamerism
It should be done under two or more different light sources, one of which should be daylight.
Color Matching
The emission of light by an object or substance exposed to radiation or bombarding particles. It makes a definite contribution to the brightness and vital appearance of a human tooth.
Fluorescence
X-rays are form of electromagnetic radiation that lie at the high-energy end of the spectrum.
Radiopacity
Polymers and Resins are
A. Radiolucent
B. Radiopaque
A. Radiolucent
Metals are
A. Radiolucent
B. Radiopaque
B. Radiopaque
What materials are added to resins to make them readiopaque?
Barium glass and Strontium glass
The thermo-physical measure of how well heat is transferred through a material by conductive flow.
Thermal Conductivity
TRUE OR FALSE: Heat flows from points of higher temperature to points of lower temperature.
TRUE
Differentiate conductors and insulators.
Conductors have high thermal conductivity. Insulators have low thermal conductivity.
Conductors - Metals
Insulators - Resins
The measure of the speed with which a temperature change will spread through an object when one surface is heated.
Thermal Diffusivity
What aids in preventing thermal shock and pulpal pain when hot or cold foods are taken into the mouth?
Low thermal conductivity and diffusivity of enamel and dentin
Example of Thermal Insulators
Glass Ionomers
Zinc Phosphate
Most Cements
Resins
The change in length per unit or the original length of a material when its temperature is raised 1°C.
Linear Coefficient of Thermal Expansion
What are the electrochemical properties?
- Tarnish
- Corrosion
INFO: A restoration may expand or contract more than the tooth during a change in temperature causing the restoration to leak or it may debond from the tooth.
Choose a material whose expansion and contraction comes closest to that of the tooth.
Differentiate Tarnish and Corrosion
Tarnish is a surface discoloration on a metal or a slight loss or alteration of the surface finish or luster. Corrosion is a process whereby metals deteriorate because of its reaction to its environment.
These are defined by the laws of mechanics, that is, the physical science that deals with energy and forces and their effects on bodies, and the resultant motion, deformation, or stresses that those bodies experienced.
Mechanical Properties
Differentiate Stress and Strain
Stress is the force per unit area of a material. It is the material’s response to force. Strain is the change in dimension or deformation of an object as a result of stress.
[When an object is exposed to a force, stress is generated within the object to counter the force and keep the object together.]
What are the different types of forces?
- Tensile
- Compressive
- Shear
TaCSay 😝
A force that tends to pull an object apart.
Tensile Force
The application of force is directed down on the object tending to squeeze it together.
Compressive Force
A force that tends to slide the top of an object over the bottom.
Shear Force
A load that tends to stretch or elongate a body; always accompanied by tensile strain.
Tensile Stress
A load that tends to compress or shorten a body. associated with compressive strain.
Compressive STress
Tends to resist the sliding of one portion of a body over another. Can also be produced by twisting or torsional action on a material.
Shear Stress
Criteria of Biocompatibility of Dental Materials
- It should not be harmful to the pulp and soft tissues.
- It should not contain toxic diffusible substances that can be released and absorbed into the circulatory system to cause a systemic toxic response.
- It should be free of potentially sensitizing agents that are likely to cause an allergic response.
- It should have no carcinogenic potential.
Refers to the ability of a material to resist applied forces without fracture or excessive deformation. It is a measure of interatomic forces collectively over the entire material.
Strength
Differentiate Yield Strength and Ultimate Strength
Yield Strength is a property that represents the stress value at which a small amount of plastic strain has occurred; the stress required to produce a given amount of plastic strain.
Ultimate Strength is the level of stress on a material at which fractures occur.
A material that does not return to its original dimension and remains bent, stretched or compressed when the force is removed.
Permanent (Plastic) Deformation
Differentiate Flexure Strength, Fatigue Strength, and Impact Strength.
Flexure Strength is a collective measurement of tensile, compressive, and shear stresses.
Fatigue Strength is the strength of a material based on a steady increase in force or cyclic loading.
Impact Strength is the energy required to fracture a material under an impact force.
Describes the relative stiffness or rigidity of a material. It is a good predictor of a material’s ability to resist bending or change in shape and is an important property for dental bridges, orthodontic wires.
Elastic Modulus (Young’s Modulus or Modulus of Elasticity)
[A material with low elastic modulus and a high tensile strength is more resistant to impact forces.]
The stress above which stress is no longer proportional to strain.
Proportional Limit (Maximal Elastic Stress)
The amount of energy absorbed by a structure when it is stressed to its proportional limit.
Resilience
The ability of a material to bend without breaking.
Flexibility
The strain associated with the stress at the elastic limit.
Maximum Flexibility
[Impression materials, which often must be severely deformed to be removed from undercuts, must have the capacity to spring back without suffering any permanent change in shape or loss of accuracy.]
Materials of low-impact resistance
- Resin-based composite
- Dental Porcelain
- Polymethylmethacrylate
- Amalgam
- Alumina Ceramic
Varies markedly from one area of the mouth to another and from one individual to another.
Higher for males than for females; greater in young adults than in children.
Mastication Forces and Stresses
Mastication forces in different areas of the mouth:
- Molar region: 90-200 lbf
- Premolar region: 50-100 lbf
- Cuspid region: 30-75 lbf
- Incisors region: 20-55 lbf
The amount of elastic and plastic deformation energy required to fracture a material and is the measurement of the resistance to fracture.
Toughness
Toughness depends on _______ and _______.
Strength and Ductility
[the strength, the ductility, the greater the toughness.]
A mechanical property that describes the resistance of brittle materials to the catastrophic propagation of flaws under an applied stress.
Fracture Toughness
[High fracture toughness = good resistance to cracking]
The relative inability of a material to sustain plastic deformation before fracture of a material occur.
Brittleness
Differentiate Ductility and Malleability
Ductility is the ability of a material to sustain a large permanent deformation under a tensile load without rupture.
Malleability is the ability of a material to sustain considerable permanent deformation without rupture under compression.
A material’s resistance to scratches and indentation. The ability of surface of a material to resist penetration by a point under a specified load.
Hardness
Types of hardness tests are:
- Barcol
- Brinell
- Rockwell
- Shore
- Vickers
- Knoop
The ability of a material to resist forces of indentation; it is also the ability of a material to resist abrasion or wear.
Hardness
TEST:
- Employed a hardened steel ball pressed under a specified load into the polished surface of a material.
- The smaller the indentation, the larger is the number and the harder is the material.
- Used extensively for metals and metallic materials.
- Not suitable for brittle materials.
Brinell Hardness Test
TEST:
- Uses a steel ball or a conical diamond point.
- The depth of penetration is measured.
- Not suitable for brittle materials.
Rockwell Hardness Test (RHN)
TEST:
- Uses a diamond in the shape of a square-based pyramid.
- Suitable for determining the hardness of brittle materials, like tooth structure.
Vickers Hardness Test (VHN)
TEST:
- Employs a diamond indenting tool.
- The impression is rhombic in outline.
- Values for hard and soft materials can be obtained by this test.
Knoop Hardness Test (KHN)
