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1. HIGH SPEEDS IN DENTISTRY
Dental handpieces and their associated equipment such as burs and
stones, are precision – manufactured instruments used for cutting, grinding, and
polishing procedures in the dental operatory as well as in the dental laboratory.
History:
Evidence of dental treatment dates back to 5000 BC.
The history of the early development of rotary instruments is incomplete
and contradictory. The development of rotary equipment was an evolutionary
process until 1946.
By the middle of the seventeenth century hand instruments were
supplemented with steel burs of various upto shapes and sizes. These were
rotated with the thumb and forefinger. The design of the interchangeable burs
with its long, straight bur were developed from this beginning, two basic
designs of handpieces and cutting instruments, straight and angle have become
standard equipment in the dental office.
The old spinning wheel and sewing machine properly inspired the
development of dental toot engine as a source of power around 1871 Rotation
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2. of cutting instrument was made possible by a long belt running over a series of
pulleys to the back of a straight hand piece.
One of the most significant advancement in the early history of
handpiece equipment was the adoption of the electric motor as a power source
in 1874. It was incorporated into a dental until in 1914. handpiece equipment
and operating speeds. Maximum of 5000 revolutions per minute remained
virtually unchanged until 1964.
Progress in dental cutting procedures was delayed by a lack of
instruments that could effectively remove hard tooth structure. The steel burs
that were used at the time could not cut enamel effectively even with
application of great force. Silicon carbide points, sometimes called
carborundum stones, were not hard enough and lost their shape rapidly.
Diamond cutting instruments were developed in Germany around 1935 but
with the outbreak of World War II and the accompanying scarcity of labour
and materials. Very few of these instruments were produced for the duration of
the war.
In a 10 year period which started in the latter part of 1946 cutting
techniques were revolutionized Diamond instruments were produced
commercially and were joined a year later by tungsten carbide burs.
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3. In 1949 it was reported that speeds of 60,000 Rpm and above were more
effective for cutting tooth structure.
From the late 18th
century many ingenious systems were devised to drive
dental rotary cutting instruments. Amongst these was the first fluid given dental
molar patented in 1865 by George F. Green. As a pneumatic tooth bur drill.
The success of Green’s pneumatic drill was relatively short lived and develops
turned their attention towards alternative power systems. In 1871 Green
himself developed the first electrically driven dental drill. Rotary power from
electric engine is transferred to the straight hand piece by belt that runs over a
series of pulleys and a three piece extension cord arm. A variable rheostat sits
on the floor and is operated by the foot to control the speed of the hand piece.
Inspite of the attention being given to foot treadle and electrically driven
engines, some interest in development of fluid driven motors was maintained in
1974, Straus patented a design for system driven by compressed air, steam or
other elastic fluid in motion in dental use by air blown from mouth through the
flexible or gum elastic tube and mouth piece.
A dental engine similar in some respects to that of Straus but powered
by water was patented by Wilkerson in 1877. This design made provision for a
fine steam of water to be directed on to the cutting instrument as the coolent.
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4. Another patented turbine hand piece with further improvement was that
of Laurence 1879. This incorporated a transmission cloth, a rotatable hand
piece sheath and a revised mechanism for the attachment of cutting
instruments. All the dental turbine described above were directly attached to
the hand piece and in use their weight would have been born by the dentist
hand.
S.S. White company later illustrated in on of their publications (1944)
avoided his problem by having its motor on a floor. It was immediately evident
that diamond and carbide instruments performed best at the highest speeds
available and increased speeds were needed for more effective cutting. The
Belgian dentist Emil Huet (1974-1944) is throughout to have been the first to
recognize the benefits of higher rotary instruments speeds. In 1911 he
developed an electric engine which reputedly achieved rotation rates of upto
10,000 Rpm. Huets engine however, proved to be unsuccessful because of over
heating and Seizure of the hand piece bearings.
In 1941 John W. Iseman was granted a patent for his design of a turbine
driven hand piece which when supplied with compressed air at 45 psi (310 kpa)
was claimed to rotate at about 25,000 rpm whereas 6000 rpm was the speed
reportedly achieved by cord driven hand piece at a time.
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5. The air abrasive techniques was available to the dental profession in
1951. The principle involves the used of powdered abrasive particles and
kinetic energy. The air abrasive techniques never became popular with the
dental professions for a number of resions.
Another non rotatory industrial cutting method known as ultrasonics
was adopted for dental use around 1952 certain disadvantages prevented
ultrasonics from becoming popular as a method for cutting tooth structures.
In 1952 Francis Callaghan was granted a patent for a design of a dental
hand piece. Which with its turbine positioned inside the hand piece head, was
distinctly different from previous fluid driven dental cutting equipment.
A belt driven angle hand piece called page – hayes become available in
1955. it was the first angle hand piece to operate successfully at speeds of
10,000 rpm and was attached to a conventional dental unit with an electric
motor as a source of power.
The most significant event in high speed development of this century
was the production. In 1957 of the first commercially viable high speed air
turbine hand piece which had been developed by J.V. Borden in 1959 a turbine
hand piece with reduced heal size (Alston mini head) was advertised in the
(UK) in 1960 the Borden Airotar ‘60’ m12 was introduced.
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6. Turbine supplied on air bearings were introduced the early 1960’s three
different models of dental air bearing hand pieces were available by 1964.
In 1991 star dental introduced the lube free hand piece incorporating
ceramic bearings which are said to require no lubrication.
Air driven hand pieces have been and continue to be the most popular
type of hand piece equipment because of the over all simplicity of design ease
of control and patient acceptance.
Gear driven hand pieces
One of the oldest and largest group of hand pieces is made up to what is
known generally as the conventional type.
Three standard designs based on use a straight hand piece, contra angle
hand piece and prophylaxis hand piece.
Rotary power is transferred to the straight hand piece by a belt that runs
from an electric over a series of pulleys and a three pieces extension cord arm.
Rotary cutting instruments are inserted in to a chunk at the front of the hand
piece. The desired angle hand piece for operation. Rotary power is transferred
from the straight hand piece by a shaft and gears inside the angle section.
Conventional hand pieces are designed to operate at speeds under 5,000
rpm. Many now have improved bearing surfaces that allow greatly increased
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7. speeds. A long sheated contra angle helps to reduce vibration. By the use of
several speed increasing transmissions it is possible to obtain speed of 1,00,000
rpm with a gear driven angle hand piece that has an automatic lubricating
system.
The most recent addition of the gear driven type of equipment is hand
piece. That has an attached miniature electric motor. The unit is light weight
has high torque and variable speeds upto 20,000 rpm.
Water driven hand pieces
In 1953 a hydraulic driven turbine hand piece was reported to operate.
Satisfactory at 60,000 rpm two year later the first commercial model called a
Turbo-Jet become available improved units have both straight and angle hand
pieces which will operate at speeds upto 1,00,00 rpm. The Turbojet is designed
as a compact mobile unit required to operate the unit water is conveyed to and
from the hand piece by a coaxial type plastic tubing. The small inner tube
caries water under high pressure to rotate a turbine in the hand piece head and
the larger outer tube returns the water to the reservoir.
Speed ranges and uses
The speed at which an instrument is rotated is referred to as revolutions
per minute of equal importance and often over looked in rotational speeds is
the diameter of the cutting instrument and width of the cut.
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8. Since 1946 continues increases in operating speeds have given rise to
large number of contradictory and confusing definitions of the various speeds
available. There speed ranges are generally available low or slow speeds
(below 6000 rpm) medium or intermidiate speeds (6000 to 1,00.000 rpm) and
high or ultra high speeds (above 1,00,000 rpm).
Low speed: Although the low speed ranges is no longer used for most type of
cavity preparation it seems logical that there will always be a need for speeds
below 6000 rpm for such operations as cleaning the teeth excavating caries,
refining cavity preparations marinating gold restorations.
Medium speed: The medium speed range 6000 to 1,00,000 rpm can be used
for cavity preparation, finishing procedures such as placement of retentive
grooves and bevels.
High speed: At speeds above 100000 rpm smaller and more versatile cutting
instruments can be used. This speed range is desirable for operations. Such as
removing old restorations obtaining form and reducing cusps.
Advantages of increased speeds
Although tooth structure can be removed by an instrument rotating at
low speeds. It is a traumatic experience for both. The patient and dentist low
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9. speed cutting is in effective and time consuming and requires relatively heavy
force of application of 2 to 4 pounds. This result in heat formation.
The main resions for increasing the speed of rotating instruments is to
increases its cutting efficiency.
1. The operator has better control and greater ease of operation.
2. Instruments lasts longer.
3. Patient are generally less apprehensive because annoying vibrations and
operating time are decreased.
4. Several teeth in the same arch can and should be treated at the same
appointment.
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10. speed cutting is in effective and time consuming and requires relatively heavy
force of application of 2 to 4 pounds. This result in heat formation.
The main resions for increasing the speed of rotating instruments is to
increases its cutting efficiency.
1. The operator has better control and greater ease of operation.
2. Instruments lasts longer.
3. Patient are generally less apprehensive because annoying vibrations and
operating time are decreased.
4. Several teeth in the same arch can and should be treated at the same
appointment.
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