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1. SPEED IN DENTISTRY
INTRODUCTION
The development of speeds in dentistry has come a long
way right from about 100A.D. fine trephine to modern ultra high
speed hand pieces. Rotary instruments are the most universally
used instrument for gross remova of tooth structure.
One of the most significant advancements was the
introduction of electric motor as a powder source in 1874. It was
incorporated into a dental unit in 1914. The initial handpiece
equipment and operating speeds remained virtually unchanged
until 1946.
With the help of variable speeds in dentistry it is possible
to perform better dentistry in less time with reduced fatigue for
both the operator and patient.
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2. HISTORY
The development of rotary equipment was an evolutionary
process up until 1946. most of the development of method for
preparing teeth has occurred within the last 100 years and
effective equipment for removal of enamel has been available
only since 1947. When speeds of 10000 rpm were first used
along with newly marketed crossbite burs and diamond
instruments.
Since 1953 continued improvements in design and
materials of construction of both hand pieces and instruments
have resulted in equipment that is efficient as well as
sterilizeable, much to the credit of manufacturers and the
profession like.
The most significant dates instruments and approximate
maximum speeds of rotation are as follows:
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3. Date Instrument Speed
1728 Hand driven instrument 300rpm
1871 Foot driven engine 700 rpm
1874 Electric engine 1,000 rpm
1914 Dental unit -
1942 Diamond cutting instrument 5,000 rpm
1946 Old units connected to increased speed 10,000 rpm
1947 Tungsten carbide burs 12,000 rpm
1951 Air abrasive Non-rotary
1952 Ultrasonics “
1953 Ball bearing handpiece 25,000rpm
1955 Water driven turbine handpiece 50,000rpm
1957 Air driven turbine angle handpiec with
ball bearing
2,50,000 rpm
1961 Air driven turbine straight handpiece 25,000rpm
1962 Air driven turbine angle handpiece with 8,00,000rpm
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4. airbearing (experimental)
1994 Contemporary air turbine handpiece 3,00,000 rpm
CLASSIFICATION
To classify and simplify terminology speed ranges
available for dental purpose are classified as follows:
a. Ultra-low speed (300-3000rpm).
b. Low speed (3000-6000 rpm).
c. Medium high speed (20,000, 45,000 rpm).
d. High speed (45,000 – 1,00,000rpm).
e. Ultrahigh speed (1,00,000 rpm and more).
f. Ultrasonic 20,000 – 25,000 rpm and sonic instruments
45,000 – 65,000.
g. Air abrasive cutting instruments.
h. Laser equipment.
Low speed cutting is ineffective, time consuming and
requires a relatively heavy force application. This results in head
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5. production at the operating site and produce vibrations of low
frequency and high amplitude of the cavity preparation and mar
the proximal margin or tooth surface.
At high speed the surface speed needed for efficient cutting
can be attained with smaller and more versatile cutting
instrument. This speed is used for tooth preparation and
removing old restorations.
Advantages are:
→ Diamond and carbide
cutting instrument remove tooth structure faster with
less pressure, vibration and heat generation.
→ The number of rotary
cutting instruments needed is reduced because smaller
size are more universal in application.
→ Instrument lasts longer.
→ Patients are generally less
apprehensive because assaying vibration and operating
time are decreased.
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6. → Several teeth in the same
arch can be treated at the same appointment.
The ultrasonic and sonic instruments:
Those are new generation of instruments that depend on the
vibrational action of energized instruments.
The ultrasonic systems is based on a system in which
sound is used as an energy source which activates the instrument
in surrounding medium. The sonic systems produce vibrations in
the available frequency range by means of compressed air, which
activates a rotor and shaft assembly as a source of vibration.
Air abrasive cutting instruments
In mid 1950’s air abrasive cutting was tested, but there
were several clinical problems that precluded general acceptance.
Now air abrasive equipment (e.g. KCP 2000) is being promoted
for stain removal and debriding pit and fissure prior to sealing
and micro-mechanical roughening of surface to be bonded.
Laser equipment
Lasers are devices which produce beams of very high
intensity, light. A large number of current and potential uses of
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7. lasers in dentistry have been identified that involve the treatment
of soft tissues and the modification of hand tooth structure. A
crystal or gas is excited to omit light photons of a characteristics
wavelength that are amplified and filtered to make a coherent
light beam.
The lasers range from long wavelength (Infra red) through
visible wave lengths, to short wave lengths (ultra violet).
Excimers are special ultraviolet lasers. At present time CO2 and
Nd:YAG lasers have shown the most promise.
Thus variable speeds and its control makes the handpiece
more versatile. This allows the operator to easily obtain the
optimal speed for the size and type of rotating instrument at any
stage of specific operation.
Biological consideration
Along with many advantages of improved equipment and
increased speeds, there are also hazards. Trauma is associated
with all operative procedures and includes not only the tooth, but
also the dental pulp, the patient and the dentist. The dentist has
the responsibility of keeping informed of the biologic as well as
mechanical aspects of dentistry.
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8. Pulp reaction to rotary cutting instrumentation
The normal human dental pulp is a highly resistant organ.
The pulp chamber is surrounded and protected by dentin and
enamel which are good insulators. As the thickness of remaining
dentin is reduced to less than 2mm, the pulp response is
increased. The closer to the pulp, the more severe the reaction
and less chance there is for recovery.
Of all operative procedures, the greatest amount of trauma
to the pulp occurs during cavity preparation. The heat generated
during the removal of tooth structure generally has been accepted
in the part as the major cause of pulp injury.
When the force on the cutting instrument is directed
downward towards the pulpal floor, more heat is produced in the
dentin which is closer to the pulp than when the cutting proceeds
towards the lateral walls.
Scientific investigators who have way research facility at
their disposal are in agreement that minimal pulp response to
cutting procedures is produced by a combination of increased
speeds, light pressure and adequate coolant.
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9. Mechanical injury to soft tissue
The lips, tongue and cheek of the patient are the most
frequent areas of soft tissue injury.
With air turbine handpiece, the rotating cutting instrument
does not stop immediately when the foot control is released. The
operator either must wait for the instrument to stop or be
extremely careful while removing the handpiece from the mouth
so as not to lacerate the soft tissue.
Air contamination
Another occupational hazard in the dental office is the
potential of cross infection that is always present when
individuals would closely together. Infectious disease such as
common cold, infectious hepatitis and tuberculosis are examples.
During, cutting procedures at increased speeds, the coolant spray
combines with the patients saliva, tooth debris and
microorganisms to form a around that is projected into the
atmosphere. Larato et al reported that large numbers of such
microorganisms are present in the air for 30 minutes.
The wearing of a surgical mark is the most effective way to
protect the patient as well as the dentist.
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10. Noise
Various sounds are known no affect people in different
ways. Soft music or rainfall usually has a releasing and sedative
quality.
High noise levels are analyzing and potentially dangerous.
Sound conditioning is just important as air conditioning or any
other aspect of the total operation.
Eye protection
The operator, assistant and patient should wear protective
glasses to prevent eye damage from flying particles during
operative procedure when cutting at ultra speeds particles at old
restoration and tooth structure are discharged at a high rate of
speed from the patients mouth.
Speed of rotation
When a dentist is cut by rotary instrument at various
speeds, an odontoblastic reaction will occur, the injury varies in
degree only. The greatest amount of odontoblastic damage occur
at speeds upto 50,000 rpm, with both belt driven and turbine
driven instruments. The least amount of damage occurs at speeds
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11. of 1,50,000 rpm to 2,50,000 rpm, protected in at a coolant is used
properly. Horsland and Shovelton (1957) and Langeland (1961)
reported that very low speeds (300-500rpm) produce an absence
of or a reduction in odontoblastic reaction.
Nature of cutting Instrument
Increase of rotational speeds and pressure by various types
of rotary cutting instruments like carbide burs, steel burs and
diamond stones cause tooth temperature increases. Apparently,
increased bur pressure also may cause displacement of
odontoblastic nuclei into the dentinal tubules.
Size of wheels and burs
The larger sizes produce greater pulp damage, owing to
increased heat generation. The peripheral speed of large disks is
significantly higher than that of a small disk at the same rpm.
Coolants
In order to reduce or eliminate the heat generated by
cutting procedures, coolants must be employed. The coolants in
use are an air spray, a combination of water and air, as a water
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12. spray, water applied through a hollow bur and water and jet
stream.
Rebound response
Bernier and Knapp (1958) described pulp injury (which
they called the rebound response) attributable to the high energy
which is released by ultrasonic cutting or by ultra-high speeds.
They said, when a cavity is prepared on one side of a tooth
reaction occurs on the opposite side. However as discussed by
Stanley (1961) and Longeland (1961), some controversy exists
about the actuality of the occurrence of rebound phenomenon.
The exact cause remains conjectural.
Recent Advancements in Speeds
Heat sterilization of handpieces has caused considerable
degeneration of handpieces moving parts and reduction in use
life. The problem of handpiece breakdown is so prevalent that
several companies have entered dental market with self repair
kits.
Oiling handpieces is suggested by most handpiece
companies to allow handpieces to function better and longer life.
But when oil is sprayed they contaminate the surgical wear
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13. impregnating tooth surface with oil debris. But to overcome this
problem Star Dental Corporation produced handpiece that do not
require oiling.
The lighting of handpieces was a development welcomed
with enthusiasm by dentists. Kavo America Corp. used Quarta
rods to light handpieces which do not degenerate heat.
Swivels were welcomed when introduced. This reduces
torque on handpiece and allows more central and precision in
cutting.
Disposable for turbine handpiece was introduced in late
1993 by oral safe Inc. CA, USA and feather touch Inc. FL, USA.
There handpieces are each within the size range of conventional
handpieces, they are manufactured from moulded plastic.
The disposable handpieces are very light compared with
conventional types.
Oral safe – 12g
Feather touch – 15.5g
Standard handpieces – 45-80gm
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14. Care and maintenance of rotary equipment
Proper handpiece maintenance
A sterilized, well running handpiece is one of the most
essential instruments dentists use. Proper handling, before and
after sterilization is outlined to ensure patients safety.
After sterilization, dry the handpiece in a water containing
sterilizer. Do not leave the handpiece in the sterilizer for a long
time. Always store the dry handpiece in a vertical position with
the head down. This insures lubricant remains in the head-
bearing areas and reduces drainage of contaminants back into the
hose.
Most handpieces can withstand temperature upto 275°F.
Steam autoclaves and chemical vapour sterilizers are commonly
used.
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15. CONCLUSION
High speed handpieces are perhaps the most important
piece of equipment in dental office. They have provided more
than 40 years of great services. However, handpieces lack of
ability to withstand the heat involved in sterilization has caused
significant problems for practitioners. Improvements and changes
are needed immediately. (Manufactures, the profession needs
your help).
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