evolution of casting machines final /orthodontic courses by indian dental academy

Evolution Evolution of of

casting casting machinemachine

INDIAN DENTAL ACADEMYLeader in continuing Dental Education

www.indiandentalacademy.comwww.indiandentalacademy.com

TABLE OF TABLE OF CONTENTSCONTENTS

•Introduction

•Timeline of casting technology

•Different Kinds Of Casting Machines

•Contemporary Dental Casting Machines

•Summary And Conclusion

•Referenceswww.indiandentalacademy.comwww.indiandentalacademy.com

INTRODUCTIONINTRODUCTION


With a history set in motion With a history set in motion before the dawn of man, before the dawn of man, metal casting was the very metal casting was the very cornerstonecornerstoneof humankind’s emergence of humankind’s emergence from the Dark Ages and its from the Dark Ages and its continued prosperitycontinued prosperity today today

.


Timeline Timel ine

of of

cast ing 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.www.indiandentalacademy.comwww.indiandentalacademy.com

•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.

.www.indiandentalacademy.comwww.indiandentalacademy.com

•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.www.indiandentalacademy.comwww.indiandentalacademy.com

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.www.indiandentalacademy.comwww.indiandentalacademy.com

•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. www.indiandentalacademy.comwww.indiandentalacademy.com

•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. www.indiandentalacademy.comwww.indiandentalacademy.com

•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.www.indiandentalacademy.comwww.indiandentalacademy.com

• (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. www.indiandentalacademy.comwww.indiandentalacademy.com

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 .www.indiandentalacademy.comwww.indiandentalacademy.com

• 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.www.indiandentalacademy.comwww.indiandentalacademy.com

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 casting

ring, balancing arm is provided with

the balancing weights.


•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.www.indiandentalacademy.comwww.indiandentalacademy.com

•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.www.indiandentalacademy.comwww.indiandentalacademy.com

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.www.indiandentalacademy.comwww.indiandentalacademy.com

•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.


SUMMARY SUMMARY

AND AND

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.www.indiandentalacademy.comwww.indiandentalacademy.com

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
