structure_of_matter general classes and principles of adhesion.ppt

STRUCTURE OF MATTER
GENERAL CLASSES
&
PRINCIPLES OF ADHESION
PRESENTED BY-
ARYA KRISHNAN
1st year PG
DEPARTMENT OF PROSTHODONTCS
Guided by
Dr Lavanya
Assistant professor
DEPARTMENT OF PROSTHODONTCS

CONENTS
 Introduction
 Change of state
 Kinetic energy
 Interatomic bonding
 Thermal energy
 Crystalline structure
 Non crystalline structure
 Diffusion
 Metals
 Ceramics
 Polymers
 Adhesion & bonding
 Conclusion

Introduction
 All matter was composed of indivisible particles called
átomos (á = “un”; tomos = “to cut”; meaning “uncuttable”),
which is the origin of the name atom
 Two or more atoms can form an electrically neutral entity
called a molecule
 Atoms & Molecules are held together by
“ATOMIC INTERACTIONS

KINETIC ENERGY
 If each molecule attains a kinetic energy that is higher than the
attraction between these molecules, they appear in the vapor form. As
the surrounding temperature decreases, the level of kinetic energy within
individual molecules decreases and the attraction between them
becomes more prominent, so that they condense to a liquid form.
 Further cooling yields a solid called ice, where the kinetic energy is low
that the molecules are immobilized by the attraction between them.

Change of State
 SOLID LIQUID GAS
 A change from the solid to the liquid state will require additional energy—
kinetic energy— to break loose from the force of attraction. This additional
energy is called the latent heat of fusion. The temperature at which this
change occurs is known as the melting temperature or fusion temperature.
 energy is needed to transform the liquid to vapor, and this quantity of
energy is known as the heat of vaporization.
 It is possible for some solids to change directly to a vapor by a process
called sublimation as seen in dry ice; this, however, has no practical
importance as far as dental materials are concerned low
Melting Temp
.
Heat of Vaporization

Interatomic
Bonding
Primary
Metallic Bonds Ionic Bonds
Covalent
Bonds
Secondary
Van der Waals
Forces
Hydrogen
Bonds

Primary Bond
A bond that forms between atoms involves the exchanging or
sharing of electrons.
Secondary Bond
A bond that involves attraction between molecules. Unlike primary
bonding, there is no transfer or sharing of electrons.

Interatomic Primary Bonding:
Interatomic primary bonding may be of three different types:
1. Ionic Bonds:
 Result from the electrostatic attraction of two atom in which one
atom transfer an electron to other atom
 The classic example is sodium chloride (Na+Cl-).
 In dentistry, ionic bonding exists in certain crystalline phases of
some dental materials, such as gypsum and phosphate based
cement .

2. Covalent Bonds:
 In many chemical compounds, two valence electrons shared by
adjacent atoms.
 The hydrogen molecule H2, is an example of covalent bonding.
 Covalent bonding occur in many organic compounds, such as dental
resin.

3. Metallic Bonds:
 It is the attraction force between positive metal ions and the
delocalized (freely moving) electrons, gathered in an electron
cloud.
 These free electrons are responsible for the high electric and
thermal conductivities of metals also for their ability to deform
plastically.
 The electrostatic attraction between the electron cloud and the
positive ions in the lattice provides the force that bonds the metal
atoms together as a solid.
 Found only in metals.

Interatomic secondary Bonding:
 In contrast with primary bonds, secondary bonds don’t share
electrons.
 Instead, charge variations among molecules or atomic groups
induce polar forces that attract the molecules.

1. Hydrogen Bonding:
 The hydrogen bond is a special case of dipole attrac
tion of polar compounds.
 Eg: water molecule . Attached to the oxygen atom
are two hydrogen atoms. These bonds are covalent.
As a consequence, the protons of the hydrogen ato
ms pointing away from the oxygen atom are not shi
elded efficiently by the electrons. They become pos
itively charged.
 On the opposite side of the water molecule, the el
ectrons that fill the outer shell of the oxygen provid
e a negative charge. The positive hydrogen nucleus
is attracted to the unshared electrons of neighborin
g water molecules. This type of bond is called a hyd
rogen bridge.
 Polarity of this nature is important in accounting fo
r the intermolecular reactions in many organic com
pounds— for example, the sorption of water by syn
thetic dental resins

2. Van der Waals Forces:
 Van der Waals Forces form the basis of a dipole attraction.
 In the case of polar molecules, dipoles are induced by an unequal sharing of electrons .
In the case of nonpolar molecules, random movement of electrons within the molecule
creates fluctuating dipoles
 Dipoles generated within these molecules will attract other similar dipoles. Such interat
omic forces are quite weak compared with the primary bonds.
 A fluctuating dipole is thus created that will attract other similar dipoles. Such inter
atomic forces are quite weak .

Interatomic Bond Distance & Bonding
Energy
 Bond Distance : Limiting factor which prevents atoms / molecules
from approaching each other too closely
 If Distance reduces – Repulsion
 If Distance increases – Attraction
 If forces of Attraction increases – Interatomic space
decreases
 Bonding Energy: Energy can be defined as a force integrated over a
distance

Interatomic energy
 In contrast with the resultant force, the
bond energy can be treated as the energy
needed to keep two atoms apart. Initially, the
bond energy decreases gradually as two
atoms come closer together.
 As the resultant attractive force passes the
peak and begins to decline rapidly, the bond
energy also decreases steeply .
 The bond energy reaches a minimum when
the resultant force becomes zero. Thereafter,
the energy increases rapidly because the
resultant force becomes repulsive and
increases rapidly with little change in
interatomic distance. The minimum energy
corresponds to the condition of equilibrium
and defines the equilibrium interatomic
distance.

Thermal Energy
 KE of atoms/molecules at a given temp.
atoms are in constant state of vibration
The atoms in a crystal at temperatures a
bove absolute zero are in a constant stat
e of vibration, and the average amplitud
e is dependent on the temperature
 If higher the temp. greater the amplitude
so, greater is the KE/ Internal Energy.
 Gross effect is expansion – k/as Thermal
Expansion

Crystalline Structure
 Atoms are bonded to each other by either primary or secondary
forces. In the solid state, they combine in a manner that ensures
minimal internal energy. The result is that they form a regularly
spaced configuration known as a space lattice or crystal.
 A space lattice can be defined as any arrangement of atom in space
in which every atom is situated similarly to every other atom. Space
lattices may be the result of primary or secondary bonds.
 All dental amalgams, cast alloys, wrought metals, gold foil are
crystalline. Some pure ceramics, such as aluminia and zirconia core
ceramics, are entirely crystalline

structure_of_matter general classes and principles of adhesion.ppt

Body centered cubic
 In the body-centered cubic (BCC)
array,
 All angles are 90 degrees and all
atoms are equidistant from one
another in the horizontal and vertical
directions. Metallic atoms are
located at the corners of the unit cell,
and one atom is at the center of the
unit cell
 Eg. iron and common for many
iron alloys

The face-centered cubic
 This array has 90- degree
angles and atomic centers that
are equidistant horizontally
and vertically, but atoms are
located in the centers of the
faces with no atom in the
center of the unit cell
 Eg Most pure metals and
alloys of gold, palladium,
cobalt, and nickel

Simple cube face centered orthorhombic Body centered orthorhombic
Simple triclinic Simple monoclinic Base centered monoclinic

Noncrystalline Solids and their Structures:
 Structures other than crystalline forms can occur in the solid state.
 For example, waxes may solidify as amorphous materials so that
the molecules are distributed at random.
 Glass – its atoms tends to develop a short order instead of long
range order (Crystalline Structure)
 A resin based composite consists of resin matrix, filler particles and
an organic coupling agent that bond the filler particles to the resin
matrix. In some cases, the filler particles are made from radiopaque
glasses that are noncrystalline.
 Other ceramics, such as porcelains, consists of noncrystalline glass
matrix and crystalline inclusions that provide desired properties,
including color, opacity, and increase in thermal expansion
coefficients, radiopacity, strength, fracture toughness .

 Composites have a noncrystalline matrix and may or may not
contain crystalline filler particles.
 The structural arrangements of the noncrystalline solids don’t
represent such low internal energies as do crystalline arrangements
of the same atoms and molecules. Noncrystalline solids do not have
a definite melting temperature, but rather they gradually soften as the
temperature is raised .

Diffusion
 In Gases & Liquid is well-known
 Atoms/Molecules diffuse in solid state as well .
 Diffusion in Crystalline structure at room temp. is very low. At
increased temp. prop. of metals may be changed radically by
atomic diffusion
 Diffusion in Non-crystalline structure may occur at rapid rate
(b.coz of disordered structure)
Diffusion Coefficient ‘D’
 Defined as Amount of Diffusion that takes place across a given
unit area

Glass Transition Temperature
 The temp. at which the sharp increase in coefficient of thermal
expansion, indicating increased molecular mobility is called Glass
Transition Temperature(Tg)
 Eg: polymers undergo transition from glossy to rubbery state
 It is characteristic of the particular glassy structure. Also known as
Glass Temperature
 Below the Tg :the material loss its fluid characterestics ,molecular
mobility decreased material become stiff

METALS
 Main feature of metals are having valence electron in outer
most shell ,it form positively charged ionic core to break
interatomic bond and establish new bond .this help metal to
establish the property of ductility and malleability
 Alloy: its mixture of two metal or non metal which provide
properties of both
 Its better explained by equilibrium phase diagram

USES OF EQUILIBRIUM PHASE DIAGRAM
 Various phase present at
different composition and
temperature
 Indicate solid solubility of one
element in other
 Shows the temperature range
over which solidification or
liquidification of material
 Indicate the temperature at which
different phase start to melt

Eutectic alloys
1) Definition: metals which are completely soluble in the liquid state but
either insoluble or partially soluble in the solid state.
Examples:
a) Lead and tin: used in soldering but not in dentistry.
b) Silver and copper: used in dental soldering and in amalgam which
improve amalgam properties."
Properties of eutectic alloys
1) they have a single melting point.
2) They have poor tarnish and corrosion resistance due to their
heterogonous structure (two phases system)
3) They are brittle because of the presence of insoluble phases (α and β)
that inhibit dislocation movement.
4) The strength and hardness are higher than those of constituent
(parent) metals because of the composite cored nature of the alloy."

Ceramics
 They are solid phase compounds of metallic and non metallic
elements
 These don’t have valence electron in outermost shell hence
they are poor conductors of heat and electrical current
 Even though it have metallic element lack characteristics of
metal substance hence considered as non metallic inorganic
structures
Structure of ceramic
 Composed of silica soda and lime in short range repetitive
order structure called glassy phase and melt at lower
temperature
 The type of material used in dentistry to balance the
translucency and opacity of prosthesis is called glass ceramics

Mechanical properties of ceramics
 Ceramic have high ionic bond as well as repulsion of
similar charges thus restrict the slippage of ions which
makes it brittle ,can’t access tensile strength lead to
fracture

POLYMER
 A class of natural and synthetic substance composed of
high molecular weight molecules with repeating unit called
macromolecules
 Each repeating unit is mer in polymer
 Molecular weight : Si unit is Dalton or g/mol

Chaining and crosslinking
 The formation of chemical bonds or
bridges between the linear polymer to as
cross linking
 Acrylic tooth are highly crosslinked to
improve its resistance to solvents, crazing
and surface stresses

Copolymer structure
 Homopolymer: only one type repeating unit
 Copolymer :two or more types of mer units
 Random :no sequential order exist among the two or more units
..ABBABABAAABAAAABABBBBABAAAABABABB..
 Block :identical monomer units occur relatively long sequences
… AAAAABBBBBBBAAAABBBBBBBAAABBBAAAA…
 Graft /branched :one type of mer {B} graft onto backbone chain{A}
... AAAAAAAAAAAAAA ...
| |
B B
B B
B B
Molecular organization
 Dental polymers are predominantly amorphous with little or no crystallinity

PHYSICAL AND MECHANICAL
PROPERTIES
Mechanical property
Plastic strain is irreversible deformation that cannot be
recovered and results in a new, permanent shape as the
result of slippage (flow) among polymer chains
 Elastic strain is reversible deformation and will be quickly
and completely recovered when the stress is eliminated, as
the result of polymer chains uncoiling and then recoiling.
 Viscoelastic strain is a combination of both elastic and
plastic deformation, but only the elastic portion is recovered
when the stress is reduced.
.

RHEOMETRIC PROPERTIES
 The rheometry, or flow behavior, of solid polymers involves a
combination of elastic and plastic deformation followed by
elastic recovery after the stresses are eliminated. This
combination of elastic and plastic changes is termed
viscoelasticity.
Solubility
The longer the chains (the higher the molecular
weight), the more slowly a polymer dissolves. •
Polymers tend to absorb a solvent, swell, and
soften rather than dissolve. Any dissolution
occurs from the swollen state.
Crosslinking prevents complete chain separation and
retards dissolution; thus, highly crosslinked polymers cannot
be dissolved

Chemical stages of polymerization
 Induction
 Activation
 Propagation
 Chain transfer
 Termination

ADHESION & BONDING
 In complete denture retention – Adhesion between Denture & Saliva &
Soft tissue
 2 substances brought into Intimate contact, one adhere to the other,
this Force is
Adhesion : In / When Unlike molecules are attracted
{Cohesion: In / When Like molecules are attracted}
 Material / film produced for Adhesion is Adhesive (fluid/semiviscous is
best)
 Material to which it is applied is Adherend

Principles of Adhesion
 Surface Energy
 Wetting
 Contact Angle of Wetting ()

Surface Energy
 At surface of lattice, energy is
greater (outermost atoms are not
equally attracted) increase in
energy per unit area of surface is
referred to as Surface Energy/
Tension
 Greater Surface energy –
greater capacity of Adhesion

Wetting
 Liquid must flow easily over entire surface & adhere to
solid
 The ability of an adhesive to wet the surface of
Adherend is influenced by cleanliness of solid surface .if
impurities over the surface less surface energy less
wetting such as epoxy
 The low surface liquid permit even spread on solid with
high surface energies

Contact Angle of Wetting
 The angle between the tangent of liquid curvature and surface
of solid
 The small contact angle indicate the adhesive force at interface
stronger than the cohesive force
 When gypsum mixed with water to make cast from impression
material ,the silicone based impression material are hydrophobic
which makes an wetting angle 90 degree .so it’s necessary to
add wetting agent/surfactant

Mechanical bonding
Strong attachment of one substance to another can also be
accomplished by mechanical means rather than by molecular attraction
ACID ETCHING
Etching of dentin surfaces primarily dissolves
Minute pores formed
Increased /improved Mechanical Retention – Decreased Marginal
Leakage, Stains, Secondary Caries & Irritation of Pulp
Internal surface of Crown / Post with cement
irregularities with Air abrasion

Bonding to tooth surface
Its complex process with following reason:
 Tooth composition is not homogenous contain both organic
and inorganic components
 A material can adhere to enamel may not adhere to dentine
 The instrument used for tooth preparation leave a rough
surface which promote entrapment at interface
 There is fluid exchange in tooth structure; the dental
adhesive should compete with water for wetting the tooth
surface by displacing it. Then too adhesive can sustain in
long term in tooth structure

Conclusion
Little knowledge is dangerous ,as rightly said ,thus a thor
ough understanding of properties of dental materials en
ables a professional to ensure the eventual success of th
e treatment.
5/20/2024

structure_of_matter general classes and principles of adhesion.ppt

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