DLA 1201, exam 3

1. Physical and
Mechanical
Properties of Dental
Materials
CHAPTER 3

2. Key Terms
 Primary bonds (AKA Chemical bonds): strong bonds with
electronic attractions; ionic bonds, covalent bonds, metallic bonds
 Secondary bonds: weaker bonds than primary bonds; hydrogen
bonds, van der Waals forces, London Dispersion forces
 Brittleness: the hardness, and the likelihood of breaking or
cracking of a material
 Density: the measure of the weight of a material compared with its
volume
 Hardness: the resistance of a solid to penetration

3. Key Terms
 Ultimate Strength: the maximal amount of stress a material can
withstand without breaking
 Elasticity: The ability of a material to recover its shape completely after
deformation from an applied force
 Stiffness: a material’s resistance to deformation
 Proportional limit: the greatest stress a structure can withstand without
permanent deformation
 Resilience: the ability of a material to absorb energy without permanent
deformation
 Toughness: the ability of a material to resist fracture

4. Key Terms
 Ductility: the ability of an object to be pulled or stretched under
tension without rupture
 Malleability: the ability to be compressed and formed into thin sheet
without rupture
 Edge strength: the strength of a material at fine margins
 Durability: the ability of a material to withstand damage due to
pressure or wear
 Viscosity: the ability of a liquid material to resist flow
 Thixotrophic fluids: liquids that flow more readily under mechanical
force

5. Key Terms
 Direct Restorative Material: Restorations placed directly into a cavity preparation
 Indirect Restorative Material: materials used to fabricate restorations outside the
mouth that are subsequently placed into the mouth
 Permanent restorations: restorations expected to be long-lasting
 Temporary restorations: restorations expected to last several days to weeks
 Intermediate restorations: restorations expected to last several weeks to months
 Shelf life: the useful life of a material before it deteriorates or changes in quality

6. Key Terms- Review
 Mixing Time: the amount of time allotted to bring the
components of a material together into a homogeneous
mixture
 Working time: the time permitted to place and manipulate
materials in the mouth
 Initial set time: the time at which the material can no longer
be manipulated in the mouth
 Final set time: the time at which the material has reached its
ultimate state

7. Key Terms- Review
 Chemical Set Materials: materials that set through a timed
chemical reaction with the combination of a catalyst and a
base
 Light-Activated Materials: materials that require a blue light
source to initiate the reaction
 Dual-Set Materials: materials that polymerize (cure) when
material is initiated by exposure to blue light source and
then continue with a chemical set reaction

8. Primary Bonds
 Aka chemical bonds
 Strongest bonds that hold atoms together because they involve the transferring or sharing of electrons
 Three types of primary bonds
 Ionic: Metal atom gives an electron to a nonmetal atam that needs extra electrons to fill its outer shell
 Both atoms now have a full outer shell, but causes them to be charged
 Materials bonded by attractive forces are brittle when they are pulled or bent and are poor electrical conductors
 Ionic bonding is also seen with gypsum and phosphate-based cements
 Covalent: occurs when two nonmetal atoms share electrons in their outer shells, creating a full shell for both.
 Very strong. Diamonds are an example
 Metallic: the electrons in the outer shells are shared among all the atoms in the lattice (+), and attracted to an
electron cloud (-)
 Free to move so they have good thermal and electrical conductivity
 Can be bent, flattened and drawn into wires

9. Secondary Bonds
Weaker than primary bonds
The weakness often leads to deformation or
fracture
No sharing or transfer of electrons occurs with
secondary bonds.
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10. Three States of Matter
 Solid
 Strongest attraction between atoms and molecules
 Have BOTH shape and volume
 Liquid
 Has volume, but no definite shape
 Gas
 Neither volume or shape
 Most materials are mixtures of more than one state of matter
 Plaster= solid + liquid

11. Solids
 A solid has a primary bond that holds it together, giving it strength
and stability.
 Strongest have a crystalline structure with molecules in regularly
spaced pattern
 If molecules of a solid are arranged in a random form with no
regular pattern, the solid is called amorphous.
 Solids are described by:
 Density
 Hardness
 Elasticity
 Stiffness
 Ductility
 Malleability
 Brittleness
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12.  Density is a measure of the weight a material has compared with its
volume.
 It is a measure of the compactness of matter, or how much mass is
squeezed into a given space.
 Hardness is the resistance of a solid to penetration.
 Hardness is used to define a material’s resistance to wear and abrasion.
 The enamel of a tooth is the hardest material
 The maximum amount of stress a material can withstand without breaking
is known as its ultimate strength.
 A material may not break when subjected to stress; rather it may deform. If
the deformation is not permanent, the material has good elasticity.
 Materials that deform permanently have reached their elastic limit.

13.  A material that is resistant to deformation has stiffness.
A material’s resistance to deformation is measured by Young’s
elastic modulus.
Stiffer materials have a higher modulus of elasticity.
 When enough force is applied to a structure, it may not be
able to recover from this force, and the structure may become
permanently deformed.
When this occurs, the material has reached its elastic or proportional
limit.
This is the greatest amount of stress a material can endure without
suffering permanent deformation.

14.  Resilience is the ability of a material to absorb energy without
permanent deformation.
 Toughness is the ability of a material to absorb energy without
fracture.
 Ductility is the amount of dimensional change that a material
can withstand without breaking.
Pulling or stretching a material (tensile stress) is a measure of its
ductility.
Materials with poor ductility are classified as brittle.
 Materials that can withstand compressive stress are considered
malleable.

15. Liquids
 The study of the flow of a material is the science of rheology.
 Molecules are not confined to a specific pattern because they flow
 The viscosity of a liquid is its resistance to flow.
 Values of viscosity depend on the nature of the material; values for thin fluids
are low, and those for thick fluids are high.
 The higher the viscosity, the greater the liquids ability to resist flow.
 Usually the viscosity of liquids decreases as the temperature increases
 Thixotropic materials are liquids that flow more easily under
mechanical forces.
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16. Application
 Materials are classified by:
 Application
 Direct restorative materials are those fabricated directly in the mouth.
 Amalgam restoration, composite resin restorations, gold foil
 Indirect restorative materials are those fabricated outside the mouth often in dental labs
using replicas of the patient’s dentition and then placed in the patient’s mouth.
 Crowns, implants, inlays, gold restorations, porcelain
 How used
 Preventative Materials: preventing occurrence of oral disease and promoting oral health
 Fluorides and sealants
 Therapeutic Materials: treatment of disease
 Medicated bases or topical treatments for periodontal disease
 Restorative Materials: largest classification, restores or replaced tooth structure, teeth or
oral tissue
 Fillings, inlay, crown, bridge, implant, or partial or complete denture
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17. Application
Expected longevity
Permanent restorations are expected to be a long-lasting
replacement of missing, damaged, or discolored teeth.
Temporary restorations, also called provisional restorations, are
used for a short period of time, several days to weeks.
Intermediate restorations, like provisional restorations, are
placed for a limited time; however, the time may extend from
several weeks to months.

18. Composition
 Components and the reactions of components may aid classification
of materials.
 Most dental materials require the combination of two components to
form the resulting final material.
 Dental materials require the combination of two components:
 Water and powder
 Liquid and powder
 Paste and liquid
 Paste and paste
 Paste and initiator (blue light)
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19. Composition
 Many components are classified as catalyst and
base.
 The catalyst is responsible for the speed at
which the reaction occurs and is often the
liquid component.
 Components may be measured and dispensed
as catalyst and base or prepackaged in
predosed amounts.
 Standardization of measurements in predose
packages eliminates the errors produced in
measuring.

20. Reaction
 When components are mixed together a reaction occurs
 The reaction may be:
 Physical
 evaporation or cooling of liquid
 Chemical
 Chemical reaction is the creation of new primary bonds.
 Most reactions of the two components result in a solid structure.
 Before the material reaches its ultimate solid state, the process goes through
stages: the manipulation stage and the reaction stage.
 Both stages are defined in units of time.
 The manipulation stage includes:
 the mixing time
 the working time
 The reaction stage includes:
 Initial set time: Begins when the material no longer can be manipulated in the mouth.
 Final set time: Occurs when the material has reached its ultimate state.
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21. Reaction
 Moisture and pressure control is essential when working with
many dental materials.
 Contamination with moisture from saliva and blood during
the initial setting time may have an adverse effect on many
dental materials, causing them to fail.
 Each material has a set mixing time, working time, and setting
time.
 In general, high temperature and high humidity will
accelerate the reaction of the material.

22. Reactions
 Types of reactions:
 Chemical set materials are those that set through the timed chemical
reaction of the catalyst and base.
 The clinician has little or no control of the time.
 Light-activated materials use a blue light source to initiate the reaction
stage.
 Both components are present in the material but do not react until
the material comes in contact with the blue light.
 This gives the clinician unlimited working time; however, the ambient
light may cause the material to begin to set.
 Dual-set materials begin with the initiation of the blue light source and
then continue with a chemical set reaction.
 This gives the clinician more control of the working time and gives
assurance of complete setting in deeper or more difficult-to-access
areas.

23. Manipulation
 Manipulation of a material’s components is
an important consideration for the dental
auxiliary.
 It is through this manipulation that the final
characteristics of the material are achieved.
 Some materials offer variation in their
manipulation; others are very technique
sensitive.
 Read all of the directions, and mix carefully;
use premeasured materials to control
accuracy.
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24. Manipulation
 Manufacturers give directions as to when variation is needed and how much variation in the ratio
the material can withstand without adverse results.
 Variables
 Ratios of components
 External variables
 temperature of the material and the room temperature and humidity
 High temperatures and humidity accelerate the reaction, and low temperatures and humidity retard the reaction.
 Shelf life
 Materials, like medications, have an expiration date.
 Shelf life may be affected by how or where a material is stored.
 Manufacturers provide this information as part of their packaging.
 Attention to the date of expiration is important for consistency in the optimal characteristics of the product.

25. Manipulation
 How materials are mixed, that is, quickly or slowly, on a
paper pad or glass slab, or by hand-mixing or using automix
dispensers, affects the final material and its consistency.
 The manipulation stage includes:
Mixing time
length of time the auxiliary has to bring the components together into a
homogenous mix
Working time
the time permitted to manipulate the material in the mouth.

26. Summary
 The success of dental materials is directly related to the choices the
dental auxiliary makes in selecting and manipulating the components
while keeping in mind those variables that cannot be altered.
 Controlling variables of manipulation and reaction stages has become
increasingly important with more sophisticated materials and more
challenging clinical situations.
 A material’s characteristics are defined by its physical structure
 Materials are available in a variety of forms
 Manufacturer’s instructions are essential to produce the best results
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