Structure of Matter, The Basic Principle of Orthodontic Materials.

1. Prepared by:
Mahmoud Kanan Mohsin
MSc Candidate, Orthodontics
Hawler Medical University
Supervised by:
Dr. Bayan A. Hassan
BDS, MSc, PhD
Hawler Medical University

2. Has many definitions, but the most
common is that it is any substance which has
mass and occupies space.

3. Is a unit of matter, the smallest unit of
an element, having all the characteristics of
that element and consisting of a
dense, central, positively charged nucleus
surrounded by a system of electrons.

4.  An atom itself is made up of three tiny kinds
of particles called subatomic particles;
1. Protons
2. Neutrons
3. Electrons

6. 1) All matter is made of atoms, atoms are
indivisible and indestructible.
2) All atoms of a given element are identical in
mass and properties.
3) Compounds are formed by a combination of
two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of
atoms.

7. An ion is an atom or molecule in which
the total number of electrons is not equal to
the total number of protons, giving the atom
a net positive or negative electrical charge. If
a neutral atom loses one or more electrons, it
has a net positive charge and is known as a
cation. If an atom gains electrons, it has a net
negative charge and is known as an anion.

8. Is an electrically neutral group of two or
more atoms held together by chemical bonds.
Molecules are distinguished from ions by
their lack of electrical charge.

9.  An alloy is a mixture or metallic solid solution
composed of two or more elements, e.g.
Amalgam, Bronze, gold alloy,…ect.

10. Is an attraction between atoms that
allows the formation of chemical substances
that contain two or more atoms.

11. Description of the structure of atoms
proposed (1911) by the British physicist
Ernest Rutherford. The model described the
atom as a tiny, dense, positively charged core
called a nucleus, in which nearly all the mass
is concentrated, around which the
light, negative constituents, called
electrons, circulate at some distance, much
like planets revolving around the Sun.

13. Primary Bond
A bond that forms between atoms and
that 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.

14. :
The forces that hold atoms together are
called cohesive forces. These interatomic
bonds may be classified as primary or
secondary. The strength of these bonds and
their ability to form after breakage determine
the physical properties of material.

15. Interatomic
Bonding
Primary Secondary
Metalic Covalent Van der Hydrogen
Ionic Bonds
Bonds Bonds Waals Forces Bonds

16. Interatomic primary bonding may be of three
different types:
1. Ionic Bonds:
 Result from the mutual attraction of positive and
negative charges.
 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 .

20.  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, in which the
compound link to form the backbone structure of
hydrocarbon chains. The carbon atom has four
valence electrons and can be stabilized by
combining with hydrogen.

22. Covalent bond formation- characterized by electron sharing

24.  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.
 Found only in metals.

28. 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.

29.  Bonds between hydrogen atom and atoms of the
most electronegative elements (N, O, F) are called
hydrogen bonds.
 When a water molecule intermingle with other
water molecules, the hydrogen (positive) portion
of one molecule is attached to the oxygen
(negative) portion of its neighboring molecule
and hydrogen bridges are formed. Polarity of this
nature is important in accounting for the
intermolecular reaction in many organic
compounds, such as the absorption of water by
synthetic dental resins.

32.  Van der Waals Forces form the basis of a dipole
attraction. E.g. in a symmetric molecule, such as
an inert gas, the electron field constantly
fluctuates.
 Normally, the electrons of the atoms are
distributed equally around the nucleus and
produce an electrostatic field around the atom.
However this field may fluctuate so that its
charge becomes momentarily positive and
negative. A fluctuating dipole is thus created that
will attract other similar dipoles. Such interatomic
forces are quite weak .

36.  In general, materials can be subdivided into
two categories according to their atomic
arrangement. In crystalline materials there is
a three-dimensional periodic pattern of the
atoms, whereas no such long range
periodicity is present in noncrystalline
materials, which possess only short-range
atomic order.

37.  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. For example, sodium
and chlorine share one electron. In the solid
state, however, the atoms do not simply form
only pairs; all of the positively charged
sodium ions attract all of the negatively
charged chlorine ions. The result is that they
form a regularly spaced configuration known
as a space lattice or crystal.

38.  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

39.  There are 14 possible lattice types or forms, but
many of the metals used in dentistry belong to
the cubic system; that is, the atoms crystallize in
cubic arrangements. All dental amalgams, cast
alloys, wrought metals, gold foil are crystalline.
Some pure ceramics, such as aluminia and
zirconia core ceramics, are entirely crystalline.
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 .

43.  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..
 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
nancrystalline.
 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 6.

45.  It’s appropriate to first consider the pure
metals, which have the simplest composition and
atomic arrangement, metals always have
crystalline structures. There are seven crystal
systems
(cubic, tetragonal, orthorhombic, rhombohedral
[trigonal] hexagonal, monoclinic, and triclinic).
Space lattice is a geometric construct wherein
each point has identical surroundings. Crystal
structures of real materials are based upon space
lattices, where there is a single atom or a group
of atoms at each space lattice point.

46.  Its most convenient to visualize the crystal
structures of metals in term of their cubic
cells, where a unit cell is the smallest portion
that can be repeated in three dimensions to
produce the crystal structure.

48.  Ceramics, which consists of more than one atomic species, can
have crystalline or noncrystalline structures, depending upon the
materials and sometimes the mode of preparation.
 Important ceramics for orthodontic application are aluminum
oxide (alumina) and zirconium oxide (zirconia), which are used
as bracket materials.
 Other ceramics are found in the powder portion of cements.
 Silicon dioxide (silica) is important filler in composite restorative
resins. The crystal structure of aluminum oxide is illustrative of
the principles involved with ceramics having substantial ionic
bonding character. The crystal structure consists of nearly
hexagonal close packed (hcp) arrangement of the larger oxygen
anions (O2), with the smaller aluminum cations (Al3+) located in
two- thirds of the octahedral interstitial sites in the hexagonal
close packed (hcp) structure .

50.  A wide variety of polymeric materials are used in
orthodontics: polyurethane elastomers for tooth
movement, adhesive resins for bonding brackets
to tooth structure, polycarbonate
brackets, elastomeric impression materials and
polycarbonate brackets. All of these polymeric
materials are based on macromolecules with
varying compositions, molecular weight and
degrees of cross linking. The polymers have
predominantly noncrystalline structures without
long range periodicity.
 Schematic polymer structure of alginate
impression material.

52.  http://physics.about.com/
 http://www.universetoday.com/
 http://www.iun.edu/~cpanhd/C101webnotes/co
mposition/dalton.html
 http://en.wikipedia.org/
 http://www.britannica.com/EBchecked/topic/514
258/Rutherford-atomic-model
 Phillips’ Science of Dental Materials, Kenneth J.
Anusavice, Eleventh Edition
 Orthodontic Materials, William A. Brantley