Evolution of Dental Casting Machines

EvolutionEvolution
ofof
castingcasting
machinemachine
INDIAN DENTAL ACADEMY
Leader in continuing Dental Educationwww.indiandentalacademy.comwww.indiandentalacademy.com

TABLE OFTABLE OF
CONTENTSCONTENTS
•Introduction
•Timeline of casting
technology
•Different Kinds Of Casting
Machines
•Contemporary Dental Casting
Machines
•Summary And Conclusion
•References
www.indiandentalacademy.comwww.indiandentalacademy.com

INTRODUCTIONINTRODUCTION

With a history set in motionWith a history set in motion
before the dawn of man,before the dawn of man,
metal casting was the verymetal casting was the very
cornerstonecornerstone
of humankind’s emergenceof humankind’s emergence
from the Dark Ages and itsfrom the Dark Ages and its
continued prosperitycontinued prosperity todaytoday
.

TimelineTimeline
ofof
casting technologycasting technology

•Casting is one of the most widely used methods
for fabrication of metallic restorations outside the
mouth.
•Since the discovery of the earth’s minerals, metal
casting has played an important role in society.
•An integral part of every technological advance,
castings have allowed us to build equipment to
feed our people, fight for democracy, build
infrastructure, manufacture canons during wars
and church bells during peace and of course
followed by cars, trains and airplanes.

•Dental casting procedures have originated from
Blacksmithery which dates back to the early
civilizations of Mesopotamia to Egypt where
utensils, weapons and tools were cast in Brass
alloys using simple techniques.
.

•The use of dental casting machines to fabricate
cast metal restoration is credited to the people of
the early Chinese civilization in the Bronze Age.
•Dental castings were first seen in the skulls of
people of the Chinese civilization where cast
metal restorations were fastened onto the human
teeth, with metal wires passing through the
space between the teeth.

•Cast restoration were also popular amongst the
people of Egyptian and Indus valley civilization
as confirmed by the human skulls found in those
sites.
•But there is little incidence on the apparatus used
by the people of these civilization.
•Some scholars emphasize that the dental castings
where carried out in the same apparatus and with
same metal as used for making weapons, tools
etc. but others differ and claim separate small
casting apparatus was used.

Breakthrough

The modern dental casting machines
came into existence only in the year of
1907 when Taggart introduced the
pressure-casting machine .

•By the beginning of the 18th century,
attempts had long been made to inlay teeth
with cemented fillings of one sort or
another.
•Techniques for the same were never
perfected and an excess of cement was
required to hold such inlays in place.
•Other methods, such as flowing gold
solder into metal matrix, resulted in a poor
seal because the gold shrank while cooling
and would not fit the cavity tightly.www.indiandentalacademy.comwww.indiandentalacademy.com

•In the 1880’s (1855-
1933), a dentist of Freeport, Illinois,
conceived of an alternative to the soldered
inlay that could be precisely cast by the
ancient disappearing wax process.
•An unusually skillful and inventive
technician, he experimented with various
procedures and by 1907 had perfected a
method of casting the first accurately
fitting gold inlays, which required the use
of casting machine which he had patented.
• He demonstrated it before the New York
Odontological Society on the evening of
January 15, 1907.
William H.TaggartWilliam H.Taggart

•The new technique involved carving
directly in the mouth a wax model of the
cavity to be filled.
•The model with a small sprue attachment
was embedded in a special plaster
investment, and the plaster heated, “burning
out” the wax.
•Gold melted with a blow pipe was then
forced into the plaster mold by means of the
casting machine, which utilized compressed
air.
•The resulting inlay fit the cavity so closely
that a very thin film of cement was needed,
serving more as a sealant than a retainer.

•This was followed by Jameson who
introduced the centrifugal-casting
machine and Solbrig who introduced the
steam-pressure casting machine.
•In the past 50 odd years lot of
advancements have been done in
improving the accuracy of the casting
machines, but little is published due to
patents.
•Different manufacturers...Few
academicians and research
scholars...studies on the accuracy...www.indiandentalacademy.comwww.indiandentalacademy.com

In 1978 ,Wilmer B. Eames and John F.
MacNamara evaluated the performance
of four different casting machines in
producing accurate and sharp margins.
They concluded that:
• Vacuum casting machines produced
sharper margins than the centrifugal
casting machines.

•There was no statistical difference in
the quality of castings produced by the
casting machines using vacuum to no
vacuum.
•Variation in density of the alloys was
not a significant factor in the relative
performance of the casting machine.

• T.E. Donovan and L.E. White in 1985 studied
the increase in castability of an alloy by increasing
the rate of acceleration of the centrifugal casting
machine.
• They used a vertical-motion centrifugal casting
machine which was rapidly accelerated by the
operation of a pneumatic cylinder and piston and
compared it with a conventional broken-arm
horizontal centrifugal casting machine.

•They concluded that vertical rotating centrifugal
casting machine was superior to the horizontal
rotating centrifugal casting machine in producing
thin sections which was critical for maximum
marginal integrity, especially important with
alloys intended for porcelain bonding.

•“William Kroll” in 1930 invented useful
metallurgical process for Ti and is considered to be
the father of Ti dentistry.
•Ti and its alloys gradually became materials of
great interest to dental researchers, because of its
attractive mechanical properties like light-weight-to-
volume, high strength-to-weight, fatigue resistance
and corrosion resistance.

•Experimentation in all aspects of Ti casting at
Universities and industries throughout the world
for the last 20 years has made Ti and Ti-alloy
casting nearly feasible for fabricating sound
cast dental prosthesis, including crowns, inlays,
and partial and complete dentures.

•The world’s first Ti dental casting was produced
in 1977 B.G. Waterstrat et al at the National
Institute of Standards and Technology in
Gaithersburg.
•In 1985, Waterstrat designed, split-chamber
argon-vacuum casting equipment which was
patented in the US.
•The idea of using this equipment for Ti casting
with magnesia investment was presented at the
JADR / AADR meeting in 1983.

•H. Hamanaka, H. Doi et al in 1989 devised a
new casting machine for dental casting of titanium
and Ni-Ti alloys.
•In this new casting machine, the gas in the mold
was removed by heating the mold in high vacuum
thus reducing the chances of oxidation of the
titanium metal/ or the alloy during casting.

•The argon gas which flooded the chamber
during the melting of the alloy was evacuated at
the starting of the casting procedure. This
prevented the inclusion of the argon gas in the
castings leading to “blow-in” porosities in the
cast structures.
•Once the molten metal / alloy dropped in the
mold from the split copper crucible, the argon
gas was again introduced which pushed the
molten metal into the mold.

•Arturo R. Hruska in 1990 introduced the Titan
Decontaminator, a device which decontaminates
the mold before the actual process of casting was
carried out.
•After the wax elimination, the mold was placed
into the Titan decontaminator and sealed with a
thin film of titanium. The air was evacuated with
the vacuum pump and helium was flushed in
with this kind of set up.
•They were able to use centrifugal casting
machines which, according to the authors, was
more, accurate in producing sharp thin margins
and the titanium castings remain uncontaminated.www.indiandentalacademy.comwww.indiandentalacademy.com

•Today there are many new machines based on the
principle of those older machines.
•More than 12 titanium casting units are now on
the market .
•Based on the casting processes utilised, three
different kinds of casting machines are available
today.

• (Centrifugal casting machine)
The alloy is melted in separate crucible by a
torch flame and the metal is cast into the
mold by centrifugal force.
• (High frequency centrifugal casting
machine)
The alloy is melted electrically by a
resistance or induction furnace, then cast
into the mold centrifugally by motor or
spring action.
• (Vacuum pressure casting machine )
The alloy is melted by a torch flame, or,
electrically, and then cast by air pressure
and / or by vacuum.

Methods of Melting the Alloys
Generally two methods are employed for
melting of metal alloy prior to casting:
• Flame / Blow pipe.
• Electrical.

FLAME
The fuel employed in most cases is a mixture
of natural or artificial gas and air, although
oxygen-air and acetylene can also be used.
The temperature of gas-air flame is influenced
by the nature of the gas and the proportion of gas
and air in the mixture. Considerable care should
be taken to obtain a non-luminous brush flame,
with combustion zones clearly differentiated for
melting the alloy .

• ELECTRICAL
There are two methods by which electricity
can be employed to melt the alloy.
• Induction.
• Electric Arc (Resistance).
Both the methods work on same principle i.e.
heat energy is produced when electric current
is passed through a conductor depending upon
the voltage applied across it.

Induction
The apparatus is simple in design
consisting of high frequency induction coil
across which high voltage is applied. This
high frequency coil surrounds the crucible
in which the alloy / metal pellets are
melted.
Two types of crucibles are used in
dentistry:
•Ceramic crucible
•Graphite crucible

Ceramic crucible
• Ceramic is a bad conductor of heat and
electricity.
• The surrounding high frequency coil
induces intrinsic “Eddy Currents” in
the alloy / metal pellets, which are
instrumental in producing heat required
to melt the alloys / metal pellets.
• The ceramic crucibles are generally
used for base metal alloys like nickel-
chrome, chrome-cobalt etc.

Graphite crucible
• Graphite is a good conductor of heat
and electricity.
• It transmits the heat produced by the
high frequency induction coil, to the
metal / alloy pellets in the crucible.
This process is the indirect heating of
the pellets in the graphite crucible.
• Noble metal alloys are generally
melted in graphite crucible.

Electric Arc / Resistance
•This is a crucible free technique where
by the metal / alloy pellet is directly
melted by the heat produced as a result
of resistance offered by it to high voltage
current.
•The apparatus consist of an electrode
and a base plate on which the metal /
alloy pellet is placed….
• The contact between the electrode
terminal and the metal / alloy pellet is in
form of an ‘electric arc’ thus the term
‘electric arc furnace’.www.indiandentalacademy.comwww.indiandentalacademy.com

Contemporary
Dental Casting
Machines

CENTRIFUGAL CASTING MACHINE
This machine utilize the centrifugal force
which is defined as a radical force
radiating outward from the center of
rotation of a body, for casting.

• The machine works on ‘broken-arm’
principle where the crucible is
attached to the broken-arm, which
accelerates the effective initial
rotational speed of the crucible and
casting ring thus increasing the
linear speed of the liquid casting
alloy as it moves into and through
the mold.
• To counter the weight of the molten
metal in the crucible and castingwww.indiandentalacademy.comwww.indiandentalacademy.com

•The metal / alloy pellets are heated in the crucible
with the flame/blowpipe and the casting ring is
positioned with the snout of the crucible fitting the
space left by the crucible former in the casting
ring.
•Once the alloy / metal is in a molten form, the
casting ring and crucible in position, the flame is
removed and the broken-arm is released and the
hand is withdrawn immediately to prevent
accidents. The broken-arm sets in rotation and
pushes the molten metal / alloy into the mold by
centrifugal force.www.indiandentalacademy.comwww.indiandentalacademy.com

•Once the metal fills the mold there is a
hydrostatic pressure gradient developed along
the length of the casting.
• The pressure gradient from the tip of the
casting to the button surface is quite sharp and
parabolic in function, coming to zero at the
button surface.
•Because of this gradient there is also a gradient
in the heat transfer rate, such that the greatest
rate of heat transfer to the mold is at the high
pressure end of the gradient (i.e. the tip of the
casting).
•Therefore, solidification progresses from tip to
the button side.

• The arm should be stopped with brake lever
only when it gets slowed down naturally, to
avoid accidents.
• The basic design of this machine is very
simple and is easy to operate. The resulting
castings are sufficiently accurate without
much defects.

Fundor T Casting machine (BEGO)
Features:
• Casting of all dental alloys (except
titanium).
• Rugged, maintenance free motor with
long service life.
• Double-jointed arm enables constant
casting quality.
• Infinitely variable starting speed.
• Quick-clamping device for fast and
secure insertion of crucibles and moulds.

•High degree of safety, by virtue of cover lock.
•High degree of stability.
•Infinitely variable mould holder.
•Automatic gas lighter as accessory simplifies
handling of the melting torch significantly.

High Frequency Centrifugal Casting
Machines
• Degutron (Degusa)Degutron (Degusa)
• The energy required here to melt the alloy is
supplied by a high frequency generator.

• The melting crucible is placed in a pivoted
centrifuge arm ,which during the melting
process is surrounded by the high frequency
generator induction coil.
• The alloy is melted by induction in a
ceramic/graphite crucible
• When the alloy has been melted ,the induction
coil is lowered and the centrifuging process is
initiated.
• The molten alloy is then forced into the
casting mold located behind the melting
crucible by means of centrifugal force.
• Oscillator and induction coil are water
cooled.www.indiandentalacademy.comwww.indiandentalacademy.com

•The casting unit is continuously cooled by the
water cooling system consisting of water tank and
an electric pump, which pumps the water from
tank into the unit via hose and sequentially water
exits the unit and flows back into the tank.
•This continuous water cycle helps in cooling the
unit which gets heated up due to high power input
thus enabling the machine to be used again and
again consecutively.

• Multicast Compact (Degusa)
Features
• Electronically – controlled starting.
• Controlled starting acceleration.
• Optimized geometry of the centrifugal arm and
distribution of weight.
• Controlled pivoting movements of the
centrifugal arm.
• Preselectable final speed.
• Quick filling of the casting mold.
• Use of all investment compounds.
• Can be used for all precious metal and Co-Cr
alloys.

Fornax G (Bego)
Features
• The only casting machine with the
superior tilting crucible system for
extremely rapid filling of the mould
cavities.
• The universal centrifugal arm : Offers a
tilting crucible for high casting quality of
precious alloys with low melting point.
And,
a normal crucible for high casting quality
of alloys with high melting point.www.indiandentalacademy.comwww.indiandentalacademy.com

•The infrared temperature limitation
system provides security when melting
precious metal alloys and helps to
avoid over heating.
•Reliable casting of alloys with
casting temp. upto 1550° C.
•Speedy casting sequence at 2min
intervals: upto 40 castings in
succession.

•Electrical and mechanical interlocks
prevent improper operations and
handling that would cause accidents.
•The induction coil cannot be raised
during the centrifugal process.
•The cover cannot be opened until the
centrifugal arm has come to a complete
stop.

MEGAPULS 3000
•Compact, easy to operate.
•Ideal for use in smaller commercial as well as
private laboratories because it can be operated
manually and has a variable heating control.

•High melting capacity with low energy
consumption.
•Homogenous melting and casting.
•Reduction in the amount of finishing required.
•Easy maintenance.
•The machine operates using high frequency
electromagnetic waves and should not be
operated by anyone with a heart pacemaker.

VACUUM PRESSURE CASTING
MACHINES
•Combilador CL-G 77 (Heraeus Kulzer)
Features
• Recommended for casting all types of crown
and bridge work in precious metal alloy.
• Electronic temperature control with digital
display.
• Max.temp. upto 1450°C.

•Larger melting crucible with prolonged
lifetime.
•Higher power for melting upto 100g alloy.
•Thermocouple fitted to avoid overheating

TITEC F210 M (OROTIG)

•It is a semi automatic titanium casting machine
where by the amount of vacuum, Argon-gas
saturation and over pressure levels as well as the
delivery of energy to electric arc to melt the
metal are automatically performed in a sequence
once the machine is started.
•Although, the decision to halt the process on the
spot and implement corrections before starting
the process again are in operators hands.www.indiandentalacademy.comwww.indiandentalacademy.com

•The rotation of the melting / casting chamber
from horizontal to vertical position for the
casting to take place, when the metal (titanium)
melting point has been optimally reached, is also
in the operators hand.
•Therefore, both the automation of the machine
and the operators skill go hand in hand to achieve
excellent results constantly.

•The basic advantage of this type of machine is
that it employs 2 vacuum sessions. The first
one enables to evacuate the gases from the
mold and thus prevents contamination of the
cast metal. The second which starts just prior to
casting prevents the inclusion of the Argon-gas
into the castings leading to “blow-in”
porosities.

•Once the molten metal is dropped in the
mold, by changing the position of the
chamber from horizontal to vertical position,
the argon gas is flooded inside the chamber.
The over pressure of 3.5 bar of Argon-gas
pushes the molten metal into the mold.

SUMMARYSUMMARY
ANDAND
CONCLUSIOCONCLUSIO
NNwww.indiandentalacademy.comwww.indiandentalacademy.com

•The beginning of the use of dental casting
procedures dates back to the early
civilizations of Mesopotamia, Egypt and
China.
•Since then history has witnessed numerous
milestones in the field of casting
technology….from the days of use of steam
pressure casting techniques, invention of
compressed air pressure casting machine by
Taggart to the modern day sophisticated
casting machines, which are based on the
principles of centrifugal force and vacuum
pressure.www.indiandentalacademy.comwww.indiandentalacademy.com

•Different manufacturers have claimed,
time to time, that their machines are
superior to the others
•A variety of casting machines with their
characteristics have been reviewed by
academicians and research scholars.
•Yet there is little practical difference seen
in the properties on accuracy of casting
made by different casting machines.
•The choice of one amongst the other is
purely a matter of personal preference.

REFERENCES
• Anusavice “Skinners science of dental
materials”. Tenth Edition.
• Asgar K., Arfaei A.H. “Castability of crown
and bridge alloys”. J Prosthet Dent 1985; 54:
60-63.
• Donovan T.E., White T.E. “Evaluation of an
improved centrifugal casting machine”. J
Prosthet Dent 1985; 53: 609-612.
• Eames B.W. “Evaluation of casting machines
for ability to cast sharp margins”. J Oper
Dent 1978; 3: 137-141.
• Hamaka H., Doi H., Yoneyama T., Okuno O.
“Dental casting of titanium and Ni-Ti alloys
for a new casting machine”. J Dent Res
1989; 68: 1529-1533.www.indiandentalacademy.comwww.indiandentalacademy.com

• Hruska A. “A novel method of vacuum
casting titanium”. Int J Prosthodont 1990; 3:
142-145.
• Laboratory manual of the requirements used
for casting – BEGO, DENTAURUM,
OROTIG,MEGAPULS 3000.
• Michael J. Lessiter, Ezra L. Kotzin, Timeline
Summer 2002,www.castsolutions.com.www.indiandentalacademy.comwww.indiandentalacademy.com

Thank you

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