Introduction
The word Ceramic can be traced back to the Greek
term keramos, meaning "a potter" or "pottery."
Keramos in turn is related to an older Sanskrit root
meaning "to burn." According to Gilman in 1967,
a ceramic is an earthy material usually of silicate
nature and may be defined as a combination of
one or more metals with a non-metallic element
usually oxygen. The American Ceramic Society
had defined ceramics as inorganic, nonmetallic
materials, which are typically crystalline in nature,
and are compounds formed between metallic and
nonmetallic elements such as aluminum & oxygen
(alumina - Al2O3), calcium & oxygen (calcia -
CaO), silicon & nitrogen (nitride- Si3N4).
In Dental science ceramics are referred to as nonmetallic,
inorganic structures primarily containing
compounds of oxygen with one or more metallic
or semi-metallic elements like aluminum, calcium,
lithium, magnesium, phosphorus, potassium,
silicon, sodium, zirconium & titanium. Ceramics
encompass such a vast array of materials that a
concise definition is almost impossible. Being an
omnipotent material, its applications are
innumerable wherein a definite boundary cannot
be established.
History
Archeologists have uncovered human-made
ceramics that date back to at least 24,000 BC.
These ceramics were originally found in
Czechoslovakia and were in the form of animal
and human figurines, slabs, and balls. The first
use of functional pottery vessels is thought to be
in 9,000 BC. These vessels were most likely used
to hold and store grain and other foods. The
ancient glass manufacturing process, which
flourished in Upper Egypt about 8,000 BC, is
closely related to making of pottery.
A French dentist De Chemant patented the first
porcelain tooth material in 1789. In 1808 Fonzi,
an Italian dentist invented a "terrometallic"
porcelain tooth that was held in place by a platinum
pin or frame. Ash developed an improved version
of the platinum tooth in 1837. Dr. Charles Land
patented the first Ceramic crowns in 1903. In 1963,
Vita Zahnfabrik introduced the first commercial
porcelain.
Ceramic Segments
The broad categories or segments that make up
the ceramic industry can be classified as follows:
Structural clay products, whitewares,
refractories, glasses, abrasives, cements and
advanced ceramics. Dental applications of
ceramics encompass most of the segments in
the ceramic industry, which includes:
Investment materials - refractories optical
modifiers - glasses, Diamond cutting tools -
abrasives, Therapeutic & esthetic dental cements
- cements and Gadgets in dental applications.
Structure
The structure of ceramic materials is dictated by
the type of atoms present, the type of bonding
between the atoms, and the way the atoms are
packed together. The atoms in ceramic materials
are held together by a chemical bond and the two
Trends Biomater. Artif. Organs, Vol 20(1), pp 7-11 (2006) http://www.sbaoi.org
8 V.G. Sukumaran and Narasimha Bharadwaj
most common chemical bonds for ceramic
materials are covalent and ionic. For metals, the
chemical bond is called metallic bond. The bonding
of atoms together is much stronger in covalent
and ionic than in metallic bonding. That is why,
generally speaking, metals are ductile and
ceramics are brittle.
Many dental ceramics contain a crystal phase and
a glass phase based on the silica structure. This
structure is characterized by a silica tetrahedran
in which a Si4+ cation is positioned at the center of
a tetrahedron with O– anions at each of the four
corners. The resulting structure is not closely
packed and has both covalent and ionic
characteristics. The regular dental porcelain, being
glassy in nature, is largely non-crystalline, and
exhibits only a short-range order in atomic
arrangement, which is referred to as dental glass
ceramics. The only true crystalline ceramic used
at present in restorative dentistry is Alumina
(Al2O3), which is the hardest and strongest oxide
known.
Ceramic structures composed of single element
are rare. Diamond is a major ceramic of this
type and the unit cell consists of carbon atoms,
each one sharing an electron with each of four
surrounding carbon atoms - hardest natural
material used to cut tooth enamel.
Properties
The properties of most ceramics are
enumerated below :
hard, wear-resistant, brittle, refractory, thermal
insulators, electrical insulators, nonmagnetic,
oxidation resistant, prone to thermal shock &
chemically stable.
However, certain ceramics do not fall into any of
these categories. Exceptions are Borosilicate
glasses (glasses that contain silica and boron
as major ingredients) and certain glass
ceramics (glasses that contain a crystalline
phase), which are highly resistant to thermal
shock. Some ceramics are excellent electrical
conductors and an entire commercial market
is based on the fact that certain ceramics
(ferrites) are magnetic.
Ceramics in Medical Applications
Ceramics are employed in a wide range in the
medical specialty. Surgeons use bioceramic
materials for repair and replacement of human
hips, knees, and other body parts. They are also
employed to replace diseased heart valves. The
applications are based on the fact that when used
as implants or even as coatings to metal
replacements, ceramic materials can stimulate
bone growth, promote tissue formation and
provide protection from the immune system.
Moreover, modern ceramic materials play an
important role in gadgets used for medical
diagnosis including both ultrasonic and X-ray
computed tomography (CT) systems.
Transducers utilizing lead zirconate titanate (PZT)
based piezoelectric ceramics are the heart of
ultrasonic systems. These transducers generate
the ultrasonic acoustic waves and detect the
reflected signals to form the image.
Gadgets for Dental Applications
Ceramics play a vital role in the manufacture and
function of various gadgets used in dental science.
Various recently introduced diagnostic and
working tools of which ceramics play an integral
part include:
Radio Visio Graphy (RVG) Pulp tester Apex
locators 1st generation - resistance based. 2nd
generation - impedance based 3rd generation -
frequency based.
Piezo Ceramics
Piezoelectricity can be defined as pressure
electricity which is a property of certain classes
of crystalline materials including natural crystals
of Quartz, Rochelle salt and Tourmaline plus
manufactured ceramics such as Barium Titanate
and Lead Zirconate Titanates (PZT). When
mechanical pressure is applied to one of these
materials, the crystalline structure produces a
voltage proportional to the pressure. Conversely,
when an electric field is applied, the structure
changes shape producing dimensional changes
in the material.
The piezoelectric materials use polycrystalline
ceramics instead of natural piezoelectric crystals.
They are more versatile