DM 3 Physical & Mechanical Properties

The mechanical and physical properties of any material are dependent on its _____________

internal structure (state of matter)

What are the three states of matter?

solid, liquid, gas

The structure of a material can be described on both a ________ and _________ level

microscopic, macroscopic

On the ________ level, we experience materials through the arrangement of its atoms and their bonding schemes

microscopic

On the ________ level, we see a material as a solid, liquid, or gas

macroscopic

Atoms contain what 3 things?

neutrons, protons, electrons

What are the 3 primary bonds of atoms?

ionic, covalent, metallic

What are the 3 secondary bonds of atoms?

permanent dipole, temporary dipole, hydrogen

Solids can either be identified as _______ and _________

rigid, crystaline

What are two different traits of liquids?

viscosity and thixotropy

A liquid’s resistance to flow

viscosity

Fluids or pastes that become thinner when agitated

thixotropy

_______ are rigid and crystalline

solids

The ________ of solids has a regular arrangement of atoms on to another

space latice

Solids ________ forces that attempt to compress or stretch the space lattice

resist

Most of our dental materials posses __________

rigidity

Liquids are _________ and have random molecules with no form

amorphous

T or F: Liquids do not have definite melting and freezing points

True

Gas has extremely _______ molecular structure

loose

_______ will completely fill and assume the shape of any container in which it is placed

gas

The properties of solids depend on the nature of the particles present (atoms, ions, molecules) and the _______ which exist between these particles

forces

What are the different types of crystalline solids?

molecular, ionic, covalent-network (atomic), metallic

________ solids have strong intermolecular forces at room temerature, using Van Der Waals forces

Molecular

Which solid best matches these traits?

• Low melting usually below 300 C

• volatile

• insoluble in water but soluble in nonpolar solvents

• non conductors of electricity

Molecular Solids

What is an example of molecular solids?

glucose and sucrose

________ solids consist of oppositely charged ions held together by strong electrical forces

Ionic

Which solid best matches these traits?

• non-volatile and high melting point

• non conductors because charged ions are in fixed position

• soluble in water (not all)

Ionic Solids

What is an example of ionic solids?

salt (NaCl)

__________ solid where atoms are held together by a network of electron pair bonds.

Covalent-Network (atomic)

Which solid best matches these traits?

• highly melting over 1000 C

• insoluble in all common solvents

• poor electrical conductors

Covalent-Network Solids

What is an example of a covalent-network (atomic) solid?

solicon dioxide, silicates

______ solids are made of atoms that are held together by metallic bonds

Metallic

Which solid best matches these traits?

• high melting points

• non volatile

• insoluble in water & common solvents

• range from soft & malleable to very hard

• excellent conductors of electricity and heat

Metallic Solids

What are physical properties of dental materials?

• melting and boiling points

• density

• viscosity

• thermal conductivity

• thermal expansion

Weight of material compared to volume; How much mass is in each space

Density

Resistance of a liquid to flow

viscosity

Measure of speed at which heat travels through a given thickness of material when one side of the material is maintained at a constant temperature 1C higher than the other side

Thermal conductivity

Measure of the heat transfer of a material in the same time-dependent state (How quickly will the interior of a crown reach the temperature of the outside)

Thermal diffusivity

What are mechanical properties of dental materials?

stress, strain, strength, stiffness, durability, ductility, hardness, fatigue, elasticity, resilience, toughness, malleability,

_________ are the substances that are present before the chemical change takes place. They are the things that are present at the starting point

reactants

___________ are the substances that are formed during the chemical change. They are the things present at the end.

products

What are common reactions with dental materials?

chain, exergonic, endergonic

A type of reaction which occurs in steps where the product of an early step serves as a reactant in a later step thereby allowing the reaction once begun, to continue.

Chain

What is an example of a chain reaction?

Crystal growth in gypsum products

A type of reaction which cannot occur by itself without input from an external source. Energy is needed to create the reaction

Endergonic (non-spontaneous)

A type of reaction that can occur by itself without input from an external source. Energy is released when the reaction happens

Exergonic (spontaneous)

What is an example of an exergonic reaction?

Iron exposed to air begins to rust

Stronger bonds and heat released =

Exergonic

Weaker bonds and heat absorbed

Endergonic

Factors which affect reaction rates include:

Catalysts, Retarders, Accelerators, Temperature, Concentration

Substances which affect the rate of a reaction without itself being used up

Catalyst

Slow down the rate at which a reaction occurs

Retarders

Speed up the rate at which a reaction occurs

Accelerators

____________ of a substance or its surrounding atmosphere can affect how quickly a reaction occurs

Temperature

The amount of a particular substance present or the purity of the substance can affect how fast or slowly a particular reaction will occur

Concentration

(higher/lower) temperature increases the speed of reactions

higher

(higher/lower) temperature decreases the speed of reactions

lower

(higher/lower) concentration increases the speed of reactions

higher

(higher/lower) concentration decreases the speed of reactions

lower

Different Classifications of Materials

composition of dental materials include:

• metals & alloys

• ceramics

• polymers

Different Classifications of Materials

applications of dental materials include:

• preventive

• therapeutic

• restorative (direct & indirect)

Different Classifications of Materials

longevity of dental materials include:

• permanent

• temporary

• intermediate

What are different components that can be used in dental materials?

• water & powder

• liquid & powder

• paste & liquid

• paste & paste

• paste & initiatior (blue light)

Which one is NOT an example of components of dental materials?

paste & powder

A reaction can be:

Physical & Chemical

What stages do the reactions occur in?

Mixing time, Working time, Initial set time, Final set time

What are ways to initate the reaction?

Chemical set materials, Light-activated materials, Dual set materials

How can you manipulate a reaction?

• ratios of components

• temp & humidity

• method of other materials involved

Solids:

rigid

Liquids:

flow

Gases:

fill container

How to remember Exergonic:

EXergonic: heat and energy EXits

How to remember Endergonic

ENdergonic: heat and energy ENters