TECHNIQUES OF CARIES REMOVAL INTRODUCTION CLASSIFICATION OF TECHNIQUES OTHER TECHNIQUES HAND PIECE ENDOSTEPPER, SMART PREP BURS, FLUORESCENCE HAND EXCAVATION AIR ABRASION AIR POLISHING ULTRASONIC INSTRUMENTATION SONO ABRASION CHEMOMECHANICAL CARIES REMOVAL LASERS CONCLUSION
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TECHNIQUES OF CARIES REMOVAL
INTRODUCTION
CLASSIFICATION OF TECHNIQUES
OTHER TECHNIQUES
HAND PIECE
ENDOSTEPPER, SMART PREP BURS, FLUORESCENCE
HAND EXCAVATION
AIR ABRASION
AIR POLISHING
ULTRASONIC INSTRUMENTATION
SONO ABRASION
CHEMOMECHANICAL CARIES REMOVAL
LASERS
CONCLUSION
TECHNIQUES OF CARIES REMOVAL
INTRODUCTION:
Caries removal or rather treatment of the infected dentine, is best defined
by outcome criteria, i.e., procedures that lead to local arrestment of the carious
process. Traditionally it includes the removal of all soft dentine, but a number of
treatment principles can be employed in order to arrest the disease locally.
The techniques used in carious dentine removal have developed since GV
Black, in 1893, initially proposed the principle of “extension for prevention” in the
operative treatment of carious lesions. He proposed that the removal of sound
tooth structure and anatomical form at sites that might otherwise encourage plaque
stagnation would help minimize caries and its progression. This was based on the
knowledge of the disease process and restorative materials available at that time.
Later, with the advent of adhesive restorative materials, newer techniques for
removal of carious dentine have been developed in an attempt to minimize this
excessive tissue loss.
There are a number of techniques available for cutting tooth tissue.
A classification of these techniques according to Banerjee, Watson and Kidd:
Category Technique
Mechanical, rotary Handpiece + burs
Mechanical, Non-rotary Hand excavators, air abrasion, air polishing, ultrasonics, sono-abrasion
Chemo-mechanical Caridex, carisolv, enzymes
Photo-ablation Lasers
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Other than the techniques mentioned in the above classification, there are
other techniques also, which include,
1) Controlled selective rotary excavation
a. Torque controlled motors
i. Endostepper
ii. Carisolv power drive
b. Polymer burs
i. Smart prep burs
c. Fluorescence aided caries excavation
Handpiece and Bur:
A carious lesion is usually penetrated and extended using ultra high speed
rotary instruments. Penetration through the carious enamel pit and fissure is
accomplished with a click No.1 or No.2 round bur. After exposing the lesion,
removal of the carious dentine progresses from the lateral borders of the lesion to
its center using round steel excavating burs in a low speed contra-angled hand
piece. As firm dentine is reached laterally, it is followed to the central area by
removal of the carious dentine. A sharp round steel bur as large as is suitable for
the size of the lesion is indicated. A positive rake angle would produce a more
acute angle on the edge of the blade (edge angle). Burs with positive rake angles
may be used to cut softer, weaker substances, such as soft carious dentin. If a
blade with a positive rake angle is used to cut a hard material such as sound
enamel or dentin, it would dig in leaving an irregularly cut surface and the cutting
edges of the blade would chip and dull rapidly.
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The steel bur has a greater number of flutes than does the carbide bur.
Hence, a smoother cutting action is achieved by using this bur and the operator is
provided with a better tactile cue. Discrimination between carious and normal
dentin must be made and a light force is applied to the bur using a wiping motion.
When the removal of the carious lesion has been accomplished using the
tactile and visual cues, clinical judgment of the caries removal can be made using
caries detecting dyes. Although, this method is quite efficient for caries removal, it
is still aversive for patients, over preparation of tissues is possible and negative
effects on the pulp could also result.
Controlled selective rotary excavation:
a) Torque controlled motors:
i) Endostepper:
It is that where the computer controlled engine makes possible a digital
attitude to the number of revolutions and torque for each individual instrument.
This system offers a patent twisting function – it is especially helpful while using
files in the root canal, where the file can free itself by an adjustable left right
movements. It causes less vibrations, that the patient hardly feels the treatment.
b) Polymer burs:
Smart prep bur:
It is a round bur made of a polymer that is only hard enough to remove
decayed dentin, stopping at the hard healthy dentin and making for a very
conservative preparation.
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As these burs are made of a material that is harder than decay yet softer
than healthy dentin, when the bur contacts healthy tissue, it becomes self-limiting.
These burs are available in 3 sizes #2, #4, #6, which seem much smaller than their
carbide round bur counterparts. They should be used at low speed i.e. 500-800 rpm
as suggested by the manufacturer, and without water spray. They should be used
with very light air brush type stroke.
Old restorations, enamel or sound dentin is removed using burs at high
speed followed by smart prep burs at low speed to remove only the decayed
dentin. As soon as the bur hits anything not as soft as decayed dentin such as
healthy dentin, affected dentin, enamel or a restoration the flutes just totally
smossh together and render the bur completely useless.
But there have been also some false positives as well with this bur.
Although the bur had flaked, but upon checking the cavity with a spoon excavator,
there was some decay left.
c) Fluorescence aided caries excavation:
Generally, carious regions can easily be overlooked and deciding whether
excavation is complete or not is often difficult. Changes in tooth fluorescence have
been used to detect early tooth surface caries for some time and is found to be one
of the reliable method.
Lennon et al. in 2002 studied the residual caries detection using visible
fluorescence. Although oral microorganisms themselves are not known to
fluoresce, several oral microorganisms were reported to produce orange-red
fluorophores as byproducts of their metabolism. For this reason, orange-red
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fluorescence in dental hard tissues may be a good marker for the zone of bacterial
invasion in dentine. The rationale for the use of visible orange red fluorescence for
this purpose is that carious dental tissue fluorescences more intensely in the red
portion of the visible spectrum (>540 nm) than the sound dentine.
In this technique, generally a violet light (370-420 nm) will be generated
using a 35 watt xenon discharge lamp and a blue band pass filter with peak
transmission at 370 nm are used. This light will be fed into the fibre-optic slow
speed hand piece so that it is focused onto the operating field during excavation.
The operator can observe the cavity through a 530 nm – high pass filter. Under
such observation, the areas exhibiting orange-red fluorescence indicate the
presence of caries which can be removed by subsequent use of an appropriate size
bur.
Lennon in 2003, conducted a study on fluorescence aided caries excavation
compared to conventional method and concluded that this method is more
effective than conventional caries excavation.
Mechanical Non-rotary:
a) Hand excavators:
Manual excavation of dental caries is done by using spoon excavator. They
are frequently used in conjunction with rotary instruments or can also be used with
other hand instruments such as enamel hatchet. The walls of the cavity should first
be extended using either rotary instruments or enamel hatchet so that the margins
of the carious area may be seen and readily approached. The extent of the lesion
should determine the size of the spoon excavator to be used. The largest excavator
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that will conveniently fit the area is selected. Sharp excavators are effective and
will reduce the force required for caries removal. The sharpened edge of the
instrument should be carefully introduced under the most accessible margin of the
carious area and gently but quickly forced under it avoiding as far as possible
pressure in the direction o the pulp. An effort should be made to lift out the entire
mass with one stroke, following as nearly as possible the hard underlying dentin.
Failing in this, a second or third sweep of the instrument from a different direction
should completely remove it. Following this, any remaining softened matter
should be gently scraped out with the same instruments and the cavity should be
cleaned.
Advantages:
1. Long term observations have shown adequate tissue removal
2. Over excavation is unlikely
3. Accepted procedure especially in pedodontics and anxious patient
4. Does not require any expensive equipment
Disadvantages:
1. High pressure causes pain
Banerjee, Kidd and Watson in 2000 studied the efficiency (time taken) and
effectiveness (quantity of dentine removal) by bur, air-abrasion, sono-abrasion and
carisolv gel compared to conventional hand excavation. From the results, it was
concluded that bur excavation was quickest but overprepared cavities relative to
the autofluorescence test, whereas carisolv excavation was slowest but removed
adequate quantities of tissue. Sono-abrasion tended to underprepare whereas air-
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abrasion was more comparable to hand excavation in both the time and amount of
dentine removed. They concluded conventional hand excavation appeared to offer
the best combination of efficiency and effectiveness for carious dentine excavation
within the parameters used in this study.
b) Air-abrasion or kinetic cavity preparation:
Dr. Robert B. Black was the first to study air-abrasives technology in
dentistry in 1943.
In 1945, he published a series of articles on the use of air-abrasive
technique for cavity preparation and oral prophylaxis.
In 1951, S.S.White introduced the first air-abrasive system – Airdent.
Air abrasion is not a complete replacement for the dental hand piece with
burs, it is merely an adjunct. Its use is limited to areas that can be easily seen and
kept free from moisture. Desired cavity details can be obtained when the technique
is augmented with hand instruments.
The principle employed by the airdent unit utilizes kinetic energy or inertia
as a rapid and not unpleasant means of removing tooth structure by incorporating a
fine abrasive material in a high velocity gaseous propellent.
Air abrasion is not a completely painless method of cavity preparation;
however it eliminate the objectionable features of vibration, bone-conducted noise,
pressure and heat. The traumatic influence on tooth structure and periodontal
tissue is reduced to a minimum.
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Bur Air abrasive
Vibration
Bone-conducted noise
Temperature rises
Pressure – 2 pounds
No vibration
No bone conducted noise
Just 1 or 2F
10 – 14 gm
In cases where the tooth is hypersensitive, pulpal stimulation may be
experienced in various degrees. Such stimulation may be controlled by reducing
the pressure of the propellant or by reducing the amount of abrasive mixed with
the propellant or both.
AIR ABRASIVE SYSTEM:
It consists of a unit, foot control and hand piece. Hand piece consists of a
handle, a shaft – an adjustable contra-angle (ball and socket) and a tip or nozzle in
a 90 relationship to the shaft.
Basic principles of air-abrasive:
Air abrasive depends for its action on a fine stream of suitable gas carrying
a controlled quantity of small abrasive particles.
Abrasive Materials:
Al2O3 – For cutting tooth substance
CaMgCO3 – Dolomite – oral prophylaxis
Studies (1950), have shown a potential of inhalational problems by air-
abrasive particles.
At present, the air-abrasive technique has US FDA approval for clinical use
of 27.5 alumina particles which has very little health hazard, both to the patient
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and the dentist. It possess a hardness of 9 on Moh’s scale and its particles possess
sharp edges and pointed corners when properly prepared.
Other materials:
Polycarbonate resin
Alumina – hydroxyapetite
Propellants:
Although compressed air may be used as a propellant, CO2 was found to
possess certain advantage for this purpose. It is,
Practically free from moisture
Non-toxic in low concentrations
Convenient and almost universally available
The pressure of the liquid CO2 varies from 700 to 1300 pounds per square
inch. This pressure is reduced to approximately 115 pounds in the line and further
reduced within the range of approximately 80 to 45 pounds at the nozzle.
Character of the abrasive stream:
The abrasives escapes from the nozzle in a cone-shaped stream, the walls of
which diverge from its long axis at an angle of approximately 3 ½ degrees. The
particles of abrasive in the stream travel at speeds in excess of 1000 feet per
second, which is well into the realm of supersonics.
In order to use the air abrasive system properly, the operator should first
understand the relation which exists between the distance at which the nozzle tip is
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held from the tooth surface and the angulation of the nozzle with respect to the
proposed cavity.
It is noted that with a nozzle tip distance of 1mm the angulation is zero. At
2 mm total angulation 0.45 it is 7. At 5mm it is 13. At 10 mm it is 23 and at
15mm it is 35.
Peruchi et al. in 2002 evaluated the cutting patterns produced by air
abrasion system with an 80 nozzle angle, 50 abrasive particle size and 80 psi air
pressure. The effects of 0.38 or 0.48 mm inner tip diameter at 2 or 5 mm from tip
to the tooth surface and 15 or 30 sec of application time on cutting efficiency were
evaluated. Statistical analysis revealed that the width of the cuts was significantly
greater when the tip distance was increased. Significantly deeper cavities were
produced by a tip with a 0.48 mm inner diameter. The application time did not
influence the cuts. They concluded that precise removal of enamel is best
accomplished when a tip with a 0.38 mm inner diameter is used at a 2mm
distance.
Cutting Speed:
There are certain influencing factors which affect the cutting speed, they
include the nature of the instrument – bur or diamond point it diameter, speed in
rpm and pressure applied.
Conversely the action of air abrasive is influenced by factors such as
propellant pressure, type and particle size of the abrasive used, abrasive mixture,
nozzle bore and length, nozzle distance from the enamel surface and nozzle
angulation.
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Studies have shown that an ordinary no.561 chrome plated dental bur is
capable of removing approximately 6mg of enamel in 30 sec at 1725 rpm when
applied with the pressure of 2 pounds. Whereas using aluminium oxide with a
propellant pressure of 80 pounds per square inch, a nozzle of 0.018 inch inside
diameter and nozzle tip distance of 7 to 13 mm with an angle of 90, air abrasive is
capable of removing 30 mg of enamel in 30 seconds.
The type and size of abrasive will affect the coarseness of the abraded
surface. The larger the size and harder the particles, the greater is the transferred
kinetic energy to the surface and thus the rougher the final finish.
Primary considerations relative to the use of air-abrasive hand piece:
Hand piece Control:
The operator must develop close co-ordination between the eye, hand and
foot. Because there is no tactile relation between the instrument and tooth being
operated on, the operator must rely solely on his visual sense. Thus, good eye sight
and good lighting are imperative for this technique.
Hand piece grasp:
Unlike the rotary hand piece, an air abrasive hand piece is always held
lightly in the pen grasp in as much as the reaction force resulting from the abrasive
stream which is only 10 to 14 gm. In accomplishing the cutting action, the
instrument is merely pointed. No pushing or pulling is ever necessary and the 3 rd
or 4th finger is generally used not as a brace but as a rest for steadying the
instrument.
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Nozzle angulation:
Nozzle angulation must be correlated with nozzle tip distance. Generally
speaking, the greater the nozzle tip distance the greater will be the angulation.
Peruchi et al. in 2001 evaluated the effect of nozzle angle and the tip
diameter on the cutting efficiency of an air abrasion system. They worked with
prep star microabrasion machine using a hand piece with either 80 or 40 nozzle
angles with 0.38 or 0.48 mm tip inner diameter. The parameters which were held
constant were abrasive particle size – 27 , air pressure – 80 psi, distance – 2mm
and duration – 15 sec. Statistical analysis revealed that the width of the cuts was
significantly greater when the cavities were prepared using the 45 nozzle angle.
Significantly deeper cavities were produced with the 80 nozzle angle. The nozzle
diameter influenced the cutting efficiency in softer substrates, dentin and
cementum. They concluded that precise removal of hard tissue is best
accomplished using the 80 angle nozzle tips for all types of surfaces, enamel,
dentin and cementum.
Basic types of cuts:
Regardless of the type, size or location of the cavity being prepared, the
principles involved for the establishment of cavity walls and floor do not vary.
There are two basic types of cuts using air abrasive hand piece.
1. Straight line cut
2. Angle cut
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1. Straight line cut:
It is employed where high degree of definition is desired. This type of cut
utilizes close nozzle distances and is precise and narrow.
2. Angle cut:
The angle cut employs the use of greater nozzle distance, together with the
required nozzle angulation. As the nozzle distance from the substance being cut
increases, the angle of the walls increases proportionately.
The advantages afforded by the employment of the angle cut are – a)
greater cutting speed and b) less visual interference.
Although there are advantages of using air-abrasion system, there are
certain limitations.
1. The nozzle of the air-abrasive instrument does not come into actual contact
with the tooth, providing no tactile guidance.
2. In case of secondary caries, it is difficult to remove the existing restoration.
3. High cost
4. When the abrasive particles strikes the surface of the mirror, it becomes
frosted.
5. Might damage the cavosurface sound tooth enamel.
Goto and Zhang in 1996, conducted a study to establish a protective
method for cavo surface sound tooth enamel during air abrasive cavity preparation
using protective varnish. Varnish was applied to the tooth surface in single, double
and triple coats. Class V cavities were then prepared on the border area of varnish
coated and intact tooth surface. The varnish was then washed off and the enamel
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margins were observed through SEM. They found that tooth surface enamel which
was coated with varnish appeared intact and the cavo-surface margin remained at a
right angle, whereas, the tooth surface enamel without varnish coating appeared
rough and the cavo-surface margin exhibited a round shape.
Waveren and Andersen in 2000 studied the quantification of surface enamel
loss and a comparison of shear bone strength. Enamel loss was determined for 2
enamel conditioning methods: acid etching with 37% phosphoric acid and sand
blasting with 50 aluminium oxide. The results showed that the enamel loss
associated with sand blasting is equal to or smaller than that resulting from acid
etching. The results also showed that the bond strength of the sandblasted groups
was significantly lower than that of the etching groups. This indicates that
sandblasting is not an alternative for the acid-etching technique currently used.
Arzu and Osman in 2004, studied the effect of air-borne particle abrasion
on the shear bond strength of four restorative materials to enamel and dentin. The
control group specimens were treated with silicon carbide paper. Restorative
materials tested were composite, compomer, GIC (L) and GIC. They concluded
that the use of air-borne particle abrasion increased the shear bond strength of
restorative materials tested to enamel and dentin.
c) Air-polishing:
It is the process by which water-soluble particles of sodium bicarbonate and
tricalcium phosphate (0.08% by weight) – to improve the flow characteristics are
applied onto the tooth surface using air pressure, shrouded in a concentric water
jet. This is the important difference between this technique and that of air-
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abrasion. As the abrasive is water soluble it does not escape too far from the
operating field. The bombardment of the hard tooth surfaces by these particles
results in a continuous mechanical abrasive action which removes surface
deposits.
Razoog and Koka in 1994, noted that increasing the air-pressure beyond 90
psi actually reduced the abrasiveness of the microprophy system. This was due to
a phenomenon found in one-dimensional, two phase fluid dynamics – choked
flow. In this phenomenon, as the air pressure exceeds the critical pressure, the
mass flow of particles will reduce thus limiting the system’s abrasiveness.
The commercially recommended use of this technique is to remove surface
enamel stains, plaque and calculus well away from the gingival margins of healthy
teeth. However, overzealous use could easily remove a considerable amount of
healthy tooth structure especially at the cervical margin. It has also been suggested
that air-polishing could be used for the removal of carious dentine at the end of
cavity preparation.
Bester et al. in 1995 studied the effect of air polishing on the dentin smear
layer and dentin. The purpose of this study was to determine the most effective
period by which the smear layer can be removed by air-abrasive polishing without
totally exposing the dentinal tubules and the effect air polishing has on dentin at
different experimental application periods with regard to the appearance of the
dentinal tubules (open or obliterated) and the amount of tissue loss from the
dentinal surface. SEM observation showed smear layer removal as an immediate
effect of air polishing. Application times of longer than 5 sec showed obstruction
of dentinal tubule opening, possibly a result of abrasive powder residue.
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Therefore, they concluded that air polishing removes the smear layer and the
amount of dentine removed corresponded to the time of application.
d) Ultrasonic instrumentation:
Nielson et al. in 1950s, indicated the possibility of using an ultrasonic
instrument to cut tooth tissue. He designed a Magnetostrictive instrument with a
25 kHz oscillating frequency. This is used in conjunction with a thick aluminium
oxide and water slurry, created by the cutting action, the mechanism of which was
the kinetic energy of water molecules being transferred to the tooth surface via the
abrasive through the high speed oscillations of the cutting tip.
It was found that the harder the tissue, the easier it was to cut. Soft, carious
dentine apparently could not be removed, but the harder, deeper layer was more
susceptible.
There are many parameters that could potentially be adjusted to alter the
cutting characteristics and Nielsen attempted to analyse the results from altering
the pressure applied, the length of use of the instrument, the powder water ratio in
the slurry, the nature of the material cut and the type of abrasive used. However,
due to the erratic and unpredictable performance of this instrument, his results
were inconclusive. Even though this method was developed only to a preliminary
stage, it was used on forty patients in a clinical trial where they found the
technique to be favorable in terms of the reduced vibration and sound generated
when compared with the dental drill.
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e) Sono-abrasion:
Further development from the original ultrasonics is the high frequency,
sonic, air scalers with modified abrasive tips – a technique known as Sono-
abrasion. The Sonicys micro unit designed by Drs Hugo is based upon the sonic
flex 2000 L and 2000 N air-scaler hand pieces that oscillate in the sonic region
(<6.5 kHz). The tip describe an elliptical motion with a transverse distance of
between 0.08 0 0.15 mm and a longitudinal movement of between 0.55 –
0.135mm. These tips are diamond coated on one side using 40 grit diamond and
are cooled using water irrigant at a flow rate of between 20-30 ml/min. The
operational air pressure for cavity finishing should be around 3.5 bar. There are
currently three different instrument tips: a lengthways halved torpedo shape (9.5
mm long, 1.3 mm wide), a small hemisphere (1.5 mm diameter) and a large
hemisphere (2.2 mm diameter). The torque applied to the instrument tips should be
in the region of 2N. If the applied pressure is too great, the cutting efficiency is
reduced due to damping of the oscillations. This technique was initially developed,
using different shaped tips, to help prepare pre-determined cavity outlines
(Sonicys) but also works well in removing hard tissue when finishing cavity
preparation.
Yozici et al. in 2002 conducted an SEM study on different caries removal
techniques on human dentine. The carious tissue was removed by hand