Ceramics in Dental Applications - Angelfire

Trends Biomater. Artif. Organs, Vol 20(1), pp 7C-1e1ra(m20ic0s6i)n Dental Applications http://www.sbaoi.or7g

Ceramics in Dental Applications

V.G. Sukumaran and Narasimha Bharadwaj

Dept. of Conservative Dentistry & Endodontics
Sree Balaji Dental College & Hospitals
Pallikaranai, Chennai 601 302

Introduction in 9,000 BC. These vessels were most likely used
to hold and store grain and other foods. The
The word Ceramic can be traced back to the Greek ancient glass manufacturing process, which
term keramos, meaning "a potter" or "pottery." flourished in Upper Egypt about 8,000 BC, is
Keramos in turn is related to an older Sanskrit root closely related to making of pottery.
meaning "to burn." According to Gilman in 1967,
a ceramic is an earthy material usually of silicate A French dentist De Chemant patented the first
nature and may be defined as a combination of porcelain tooth material in 1789. In 1808 Fonzi,
one or more metals with a non-metallic element an Italian dentist invented a "terrometallic"
usually oxygen. The American Ceramic Society porcelain tooth that was held in place by a platinum
had defined ceramics as inorganic, nonmetallic pin or frame. Ash developed an improved version
materials, which are typically crystalline in nature, of the platinum tooth in 1837. Dr. Charles Land
and are compounds formed between metallic and patented the first Ceramic crowns in 1903. In 1963,
nonmetallic elements such as aluminum & oxygen Vita Zahnfabrik introduced the first commercial
(alumina - Al2O3), calcium & oxygen (calcia - porcelain.
CaO), silicon & nitrogen (nitride- Si N ).
Ceramic Segments
34
The broad categories or segments that make up
In Dental science ceramics are referred to as non- the ceramic industry can be classified as follows:
metallic, inorganic structures primarily containing
compounds of oxygen with one or more metallic Structural clay products, whitewares,
or semi-metallic elements like aluminum, calcium, refractories, glasses, abrasives, cements and
lithium, magnesium, phosphorus, potassium, advanced ceramics. Dental applications of
silicon, sodium, zirconium & titanium. Ceramics ceramics encompass most of the segments in
encompass such a vast array of materials that a the ceramic industry, which includes:
concise definition is almost impossible. Being an
omnipotent material, its applications are Investment materials - refractories optical
innumerable wherein a definite boundary cannot modifiers - glasses, Diamond cutting tools -
be established. abrasives, Therapeutic & esthetic dental cements
- cements and Gadgets in dental applications.
History
Structure
Archeologists have uncovered human-made
ceramics that date back to at least 24,000 BC. The structure of ceramic materials is dictated by
These ceramics were originally found in the type of atoms present, the type of bonding
Czechoslovakia and were in the form of animal between the atoms, and the way the atoms are
and human figurines, slabs, and balls. The first packed together. The atoms in ceramic materials
use of functional pottery vessels is thought to be are held together by a chemical bond and the two

8 V.G. Sukumaran and Narasimha Bharadwaj

most common chemical bonds for ceramic materials for repair and replacement of human
materials are covalent and ionic. For metals, the hips, knees, and other body parts. They are also
chemical bond is called metallic bond. The bonding employed to replace diseased heart valves. The
of atoms together is much stronger in covalent applications are based on the fact that when used
and ionic than in metallic bonding. That is why, as implants or even as coatings to metal
generally speaking, metals are ductile and replacements, ceramic materials can stimulate
ceramics are brittle. bone growth, promote tissue formation and
provide protection from the immune system.
Many dental ceramics contain a crystal phase and
a glass phase based on the silica structure. This Moreover, modern ceramic materials play an
structure is characterized by a silica tetrahedran important role in gadgets used for medical
in which a Si4+ cation is positioned at the center of diagnosis including both ultrasonic and X-ray
a tetrahedron with O– anions at each of the four computed tomography (CT) systems.
corners. The resulting structure is not closely Transducers utilizing lead zirconate titanate (PZT)
packed and has both covalent and ionic based piezoelectric ceramics are the heart of
characteristics. The regular dental porcelain, being ultrasonic systems. These transducers generate
glassy in nature, is largely non-crystalline, and the ultrasonic acoustic waves and detect the
exhibits only a short-range order in atomic reflected signals to form the image.
arrangement, which is referred to as dental glass
ceramics. The only true crystalline ceramic used Gadgets for Dental Applications
at present in restorative dentistry is Alumina
(Al2O3), which is the hardest and strongest oxide Ceramics play a vital role in the manufacture and
known. function of various gadgets used in dental science.
Various recently introduced diagnostic and
Ceramic structures composed of single element working tools of which ceramics play an integral
are rare. Diamond is a major ceramic of this part include:
type and the unit cell consists of carbon atoms,
each one sharing an electron with each of four Radio Visio Graphy (RVG) Pulp tester Apex
surrounding carbon atoms - hardest natural locators 1st generation - resistance based. 2nd
material used to cut tooth enamel. generation - impedance based 3rd generation -
frequency based.
Properties
Piezo Ceramics
The properties of most ceramics are
enumerated below : Piezoelectricity can be defined as pressure
electricity which is a property of certain classes
hard, wear-resistant, brittle, refractory, thermal of crystalline materials including natural crystals
insulators, electrical insulators, nonmagnetic, of Quartz, Rochelle salt and Tourmaline plus
oxidation resistant, prone to thermal shock & manufactured ceramics such as Barium Titanate
chemically stable. and Lead Zirconate Titanates (PZT). When
mechanical pressure is applied to one of these
However, certain ceramics do not fall into any of materials, the crystalline structure produces a
these categories. Exceptions are Borosilicate voltage proportional to the pressure. Conversely,
glasses (glasses that contain silica and boron when an electric field is applied, the structure
as major ingredients) and certain glass changes shape producing dimensional changes
ceramics (glasses that contain a crystalline in the material.
phase), which are highly resistant to thermal
shock. Some ceramics are excellent electrical The piezoelectric materials use polycrystalline
conductors and an entire commercial market ceramics instead of natural piezoelectric crystals.
is based on the fact that certain ceramics They are more versatile with physical, chemical
(ferrites) are magnetic. and piezoelectric characteristics able to be tailored
to specific applications. The hard, dense ceramics
Ceramics in Medical Applications can be manufactured in almost any given shape
or size, which are chemically inert and immune
Ceramics are employed in a wide range in the to moisture and other atmospheric conditions.
medical specialty. Surgeons use bioceramic

Ceramics in Dental Applications 9

Therapeutic Ceramics POROUS: Attached by vascularization through
pores. e.g, Porous Alumina.
Silicate cement
SURFACE ACTIVE: Directly attach by chemical
Silicates constitute the first dental cement to use bonding with bone.e.g, Bioglass, Hydroxyapatite
glass as its component. The cement powder is a
glass consisting silica, alumina and fluoride RESORBABLE Designed to be slowly replaced
compounds. The liquid, on the other hand, is an by bone.e.g, Tricalcium Phosphate
aqueous solution of phosphoric acid with buffer
salts. The cement powder and liquid are mixed Ceramics In Esthetic Dentistry
together resulting in an acid-base reaction. Fluoride
ions are leached out from the set cement, which Composite Resins
is responsible for the anti-cariogenic property
exhibited. The evolution of composites has opened up new
vistas in the art and science of Esthetic dentistry.
Glass Ionomer Cement (GIC) Composites constitute an array of materials
composed of Bisphenol A Glycidyl dimethacrylate
Glass ionomer cement represents a logical step resin, Organosilane coupling agents, Silica fillers,
in the evolution of therapeutic cements. They Glass modifiers & Metallic oxides. The advent of
constitute an improved version of the silicate composite resins has virtually replaced most of
cement, in which the liquid is replaced by the restorative materials in dentistry.
carboxylic acids with glass remaining as the
powder. It is the most popular dental cement that Classification Of Dental Ceramics
is used in various aspects. The highlight of this
material is demonstrated by its superior Dental ceramics can be classified in a variety of
biocompatibility and anti-cariogenic property. ways.
Modifications of glass ionomer cement include the
high density Glass ionomers, packable ionomers Based on Composition
for use in Atraumatic Restorative Treatment (ART).
Resin modified Glass ionomer cements Silicate ceramics- characterized by
incorporate resins in their powder component for amorphous glass phase. Main component is silica
better strength. - SiO . Oxide ceramics contain a principal

Bioceramics 2

Bioceramics are a group of ceramics, which are crystalline phase like Alumina. Oxides of Zirconia
biologically active materials rich in calcium and has very high fracture toughness. Non-oxide
phosphate. Hydroxyapatite and tricalcium ceramics not used in dentistry; they possess high
phosphate are similar in composition to bone and processing temp, complex processing methods
teeth and can be used for augmentation of alveolar and high degree of opacity eg. Carbides nitrides.
ridges and filling bony defects. They are Glass ceramics are type of ceramics that contains
manufactured and are available in block, granular a glass matrix phase & at least one crystal phase.
and injectable forms. These bioactive materials
are packed in the required site providing a scaffold Based on Type
for new bone growth and are Osseo-inductive in
nature. The various forms of bioceramics are Feldspathic porcelain. Leucite - reinforced
Single crystals (Sapphire), Polycrystalline porcelain., Aluminous, porcelain. Glass infiltrated,
(Hydroxyapatite) Glass (Bioactive glass) Glass alumina.Glass, infiltrated zirconia. and Glass
ceramics (Ceravital) Composites (Stainless steel ceramics.
reinforced Bioglass)
Based on firing temperature
Types of Bioceramics
Ultra-low fusing< 850°C (1562°F) Low fusing
There are about four types of bioceramics: 850°C - 1100°C (1562°F - 2012°F) Medium Fusing
1101°C - 1300°C (2013°F - 2072°F) High fusing
INERT: Attached by compact morphological 1300°C (2372°F)
fixation. e.g, Alumina, Carbon
Based on sub-structure metal

Cast Metal, Swaged metal, Glass ceramics
Sintered core ceramics andCAD-CAM porcelain

10 V.G. Sukumaran and Narasimha Bharadwaj

Based on use or indications and transmission of light compared to metal-
ceramics, all Ceramics were developed.
Denture teeth fixed partial dentures, Full crowns Natural teeth always permit diffuse
Veneers, Inlays Post & Cores. The most practically transmission and regular transmission.
applied classification includes: - Metal Ceramics
(Porcelain fused to metal) Metal free Ceramics Artificial tooth must possess a depth of
(All Ceramics). The various types of metals in translucency to simulate natural teeth, which is
metal ceramics include Gold alloys,Gold alloys + made a reality in All-Ceramic restorations.
base metals like iron, indium & tin. Pure metals
like commercially pure Titanium, Platinum, gold Types of All ceramic restorations
and palladium alloys and Base metal alloys (Nickel,
chromium). Aluminous porcelain. Glass Ceramics
Castable, Machinable and Pressable
Four types of process for producing a metal Glass infiltrated, CAD-CAM and Cercon
coping, Electrodeposition of gold or other metal Zirconia system.
on a duplicate die, Burnishing and heat treating
metal foils on a die. CAD-CAM processing of a Aluminous porcelain is composed of a glass
metal ingot. Casting of a pure metal or an alloy matrix phase and at least 35 vol% of Alumina. It
(predominantly base metal) through the lost wax is one of the commonly used core ceramic and
process. utilizes a thin platinum foil when employed with
all ceramic restorations. Aluminous core is
Feldspathic porcelain stronger than feldspathic porcelain when used
in metal ceramic restorations.
Feldspars are used in the preparation of many
dental types of porcelain designed for Porcelain Glass ceramic consists of a glass matrix phase
fused to metal (PFM) restorations. Potassium and and at least one crystal phase that is produced
sodium feldspar are naturally occurring minerals by the controlled crystallization of glass. It is
composed primarily of Potash and soda. The most available is Castable, machinable, pressable
important property of feldspar is its tendency to and infiltrated forms which is used in all ceramic
form crystalline mineral leucite when melted. restorations. The first commercially available
Leucite is nothing but potassium aluminium castable glass ceramic is Dicor. These
silicate mineral with large co-efficient of thermal ceramics are formed into the desired shape by
expansion compared with glasses. The property the lost wax casting process followed by coating
of Feldspar to form Leucite is taken advantage in with veneering porcelain. The significant aspect
the manufacture of porcelains for metal bonding. of this ceramics is the Chameleon effect
in which a part of color is picked up from
Advantages of Metal ceramics adjacent tooth.

High strength. Utilizes the sub-structure metal The Machinable glass ceramic is a high quality
coping to withstand stresses. Thermal product that is crystallized by the manufacturer
compatibility. Less crack propagation. High and provided as CAD-CAM blanks or ingots.
resistance to fracture. They are more precise than castable glass
ceramic as the errors involved in the casting
Drawbacks process are eliminated. They possess
mechanical properties, which are similar to
Inadequate structure for ceramics - thickness of castable forms but are less translucent than
metal coping. More occlusal clearance required. them. The Pressable glass ceramic is one,
Transparent metallic hue - anterior teeth. Metal which involves pressure molding in the
exposed in case of gingival recession. Patients manufacture. A piston is used to force a heated
allergy to metals. Casting procedural errors with ceramic ingot through a heated tube into a mold,
metals. Bonding failures at porcelain-metal where the ceramic form cools and hardens to the
interface due to oxide layer production. shape of the mold. When the object is solidified,
the refractory mold is broken apart and ceramic
All ceramics piece is removed. Hot pressing occurs over a 45
min period at a high temperature to produce the
With a view to bring-in closer shade match,
enhanced esthetics through better diffusion

Ceramics in Dental Applications 11

ceramic sub-structure. Core structure is then Cerec CAD-CAM unit are ceramics supplied in
stained, glazed or coated by veneering porcelain, small blocks that can be ground to the desired
which results in translucent ceramic core, restorative pattern by computer driven CAD-CAM
moderately high flexural strength, excellent fit & system. In Cercon ceramic systems, following
excellent esthetics. Eg. IPS Empress 1 & IPS tooth preparation impression is made and wax
Empress 2. pattern is fabricated. The wax pattern is anchored
on the left side of the scanning and milling unit
Glass infiltrated ceramic is used as one of the 3 called as Cercon Brain and a pre-sintered zirconia
core ceramics namely, In-Ceram Spinell, blank is attached to the right side of the Brain
In-Ceram Alumina and In-Ceram Zirconia. They unit. The blank has an attached barcode, which
utilize the technique of slip-cast on a porous contains the enlargement factor and other
refractory die and heated in a furnace to produce parameters for milling procedure.
a partially sintered coping or framework which
is infiltrated with glass at 11000C for 4 hrs to The Future Of Dental Ceramics
strengthen the slip-cast core. They possess
relatively high flexural strength and ability to be The proven track record of dental ceramics in
successfully cemented using any cement. all areas of direct and indirect restorative
CAD-CAM involves a technique wherein the dentistry would soon offer the dental operatory
internal surface is ground with diamond discs the extra power needed to produce more
to the dimensions obtained from a scanned predictable and perfect all round biofunctional
image of the preparation. and bioesthetic restoratives.

References

1. Science of Dental materials by Kenneth J Anusavice ; 11th edition ; pg
2. Ceramic whitewares - their technologies & applications by Sudhir Sen ; 1992 ; pg 48 - 62.
3. Ceramics - Physical & chemical fundamentals by Hermann Salmang ; 1961 ; pg 165 - 184.
4. Introduction to the principles of Ceramic processing by James S Reed ; 2001 ; pg 55 - 73.
5. Evolution of dental ceramics in the twentieth century. John McLean & Podont ; Jour of Prosthet Dent 2001 ;

85 ; 61 - 66.
6. The science & art of dental ceramics by John W McLean ; volume I & II ; 2000 ; pg 165 - 304.
7. Recent developments in Restorative dental ceramics by Kenneth J Anusavice ; JADA - 1993 ; 124 ; 72 - 81.
8. A review of All-Ceramic restorations by Marc A Rosenblum & Allan Schulman ; JADA - 1997 ; 128 ; 297 - 305.
9. The strength of dental ceramics by Messer, Piddock & Lloyd ; Jour of Prosthet Dent 1991 ; 19 ; 51 - 55.