Ultrasonic and sonic instrumentation are techniques used in endodontics that involve imparting sinusoidal vibrations to endodontic files at ultrasonic or sonic frequencies. While both techniques activate files vibrationally, they differ in power source, frequency, handpieces, and files used. Studies have found that while ultrasonics can efficiently remove dentin, controlling file position makes it difficult for precise root canal shaping, especially in the apical region. In contrast, sonics may offer superior efficiency due to its longitudinal oscillatory pattern that is less impeded in narrow canals. Both techniques show promise but proper understanding and use of their characteristics is important to avoid risks like ledging, perforation or

1. SONICS AND ULTRASONICS
IN ENDODONTICS
INDIAN DENTAL ACADEMY
Leader in Continuing Dental Education
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2. CONTENTS
INTRODUCTION
EVOLUTION
AN INSIGHT
The Physics behind Ultrasonics
The Physics behind Sonics
BIOPHYSICAL EFFECTS OF ENDOSONICS
Cavitation
Acoustic Streaming
IRRIGANTS
ULTRASONICS
SONICS
A COMPARATIVE ANALYSIS
Shaping of Root Canals
Canal Debridement
Root end Preparation
Endodontic Re-treatment
Intraradicular Post Removal
Silver Point Removal
Gutta Percha Removal
Sealer Placement and Gutta Percha Obturation
CONCLUSION
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3. EVOLUTION
Ultrasonic instrumentation was first introduced into dentistry in the form of a drill (Ctuna,
1953; Balamuth, 1967)
Such instruments were used with abrasive slurry for the preparation of tooth cavities prior
to restoration
This technique however was superseded by the advent of the high-speed hand piece and
a further development took place when Zinner (1955) recorded the use of an ultrasonic
instrument to remove deposits from the tooth surface
Johnson and Wilson (1957) improved upon the instrumentation and the ultrasonic scalar
became established in the removal of dental plaque and calculus
The idea of utilizing ultrasound in Endodontic therapy was suggested in 1957 by Richman
This was not fully developed until 1976, when Martin developed a commercial system
harnessing the properties of ultrasonic energy in the preparation and cleaning of the root
canal
Tronstadt et al in 1985 were the first to report on the use of a sonic instrument for
Endodontics
These techniques were termed as Endodontics by Martin and Cunningham and have now
become a well recognized endodontic procedure.
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4. AN INSIGHT
Endosonics denotes a device, which imparts sinusoidal vibration of high intensity to a
root canal instrument
The range, which is either or above that of audible perception, i.e. at ultrasonic
frequencies (20-42 kHz)
Both ultrasonic and sonic instruments are, however, similar in design, in that they consist
of driver, at the end of which is clamped an endosonic file usually at an angle of 60 to 90
to the long axis of the driver
It is the oscillatory pattern of the driver that determines the nature of movement of the
attached file
Endosonic instrumentation differs from hand and rotary instrumentation since the cutting
of dentin is facilitated by a mechanical device that imparts a sinusoidal motion to the
instrument by the transfer of vibrational energy along the shaft.
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5. The Physics behind Ultrasonics
There are two basic methods of producing ultrasound
The first is Magnetostriction, which converts electromagnetic energy into mechanical
energy
A stack of magnetostrictive metal in the handpiece is subjected to a standing and
alternating magnetic field, as a result of which, vibrations are produced
The second method is based on the Piezo-electric principle
A crystal is used which changes dimensions when an electrical charge is applied
This crystal deformation is converted to mechanical oscillation with no production of heat
The magnetostrictive units have the disadvantage, when compared with the
Piezo-electric, that the stack generates heat and must be cooled
This means tubing is required to carry water to the hand piece, and if the irrigant is
sodium hypo chloride, then the water has to be led away by more tubing, after cooling the
stack
A separate source by more tubing carries the sodium hypochlorite to the head of the
hand piece
Both these types work at ultrasonic frequencies and exhibit similar patterns of the
oscillation
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6. At the ultrasonic frequencies used, the main driver oscillates in a true longitudinal
manner, and as it moves back and forth a transverse wave is generated along the length
of the endosonic file
This transverse oscillation is characterized by a series of Nodes and Antinodes along the
length of the file, the nodes representing sites of minimum oscillation of displacement of
the file and the antinodes representing sites of maximum oscillation or displacement
The tip of the file that is totally unconstrained will oscillate with the greatest displacement
from rest
It is this motion of the file that almost certainly causes abrasion (filing) of the canal walls
when the instrument is moved vertically within the canal
The energy contained in the transverse oscillation of the file is low, however, compared
to that of the driver
Consequently, if the file is constrained within a tightly fitting canal the oscillatory pattern
will be reduced or even eliminated
This is inefficient and more likely to occur in curved canals than straight ones
It is apparent that transverse oscillation is not a particularly effective mode of movement
for an endodontic procedure, as it may result in irregular cutting of dentin or uncontrolled
filing in the apical third of the root canal – dependent upon whether the file is constrained
or free with the canal
A true longitudinal action of the file would be an advantage, as this would enable a filing
action to take place along the total length of the root canal.
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7. The Physics behind Sonics
Sonic instruments rely on the passage of pressurized air through the instrument hand
piece in order to use, operating at either or around 3-65 kHz
The sonic instruments have a main driver, which in contrast to the ultrasonic driver
produces an elliptical pattern of oscillation during activation
When the attached file is operated in air without any physical constraint, it sets up a
circular motion characterized by single antinodes at the tip and a node near the driver
The action of the driver imparts both a vertical and lateral component to the action of the
file
When the file is constrained is essentially eliminated, and a true vertical or longitudinal
file movement remains
This difference is oscillatory pattern may explain the reportedly superior efficiency of the
sonic instrument during clinical use.
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8. BIOPHYSICAL EFFECTS OF ENDOSONICS
Cavitation
Cavitation is defined as the growth and subsequent violent collapse of a small gas filled
pre-existing in homogeneity in the bulk fluid
When a vibrating object is immersed in a fluid, oscillations are set up in the fluid, which
cause local increases (compression) and decreases (rarefaction) in fluid pressure
During the rarefaction phase, at certain pressure amplitude, the liquid can fail under
acoustic stress and form cavitation bubbles
During the next positive pressure phase, these primarily vapor filled cavities implusively
collapse, producing radiating shock waves
Cavitation has been shown to be useful in the removal of tooth deposits during operation
of the ultrasonic scaler, as the scaler has a larger surface area and displacement
amplitude, and thus is able to generate the threshold acoustic pressure amplitude
necessary to induce cavitation
Although it is theoretically possible that cavitational activity occurs also around the
oscillating endosonic file, it is highly unlikely that a confined area such as a root canal
would increase the probability of cavitation inception.
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9. There are several reasons for this:
The threshold power setting at which this phenomenon would occur is beyond the range
that is normally used for endodontic purposes
Cavitation inception depends on free displacement amplitude of the file. This would be
impossible to achieve during instrumentation, as damping of the displacement amplitude
is inevitable when the file contacts the canal walls
The conditions under which a boundary would enhance acoustic cavitation is one in
which there would be a reflection of acoustic energy from the boundary with such a phase
change as to lead to generation of standing waves within the volume of the liquid being
examined
Since it is necessary for such a boundary to be at least one half wavelength away, and
the wavelength of sound in water at a frequency of 25 kHz is 6 cm, the production of
standing waves (and thus cavitation enhancement due to doubling of the acoustic
pressure amplitude) would not be possible within a root canal
A root canal has thus to be at least 6 cm in diameter for standing waves to form, which
one does not encounter clinically
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10. Acoustic Streaming
Acoustic streaming is defined as the generation of time independent, steady
unidirectional circulation of fluid in the vicinity of a small vibrating object
When a vibrating file is immersed in a fluid, the file is observed to generate a streaming
fluid comprising two components:-
The primary field consisting of rapidly moving eddies in which the fluid element
oscillates about a mean position
Thesuperimposed secondary field consisting a patterns of relatively slow, time I
ndependent flow
Characterstically the fluid is transported from the apical end to the coronal end
These flows of liquid have a small velocity, of the order of a few centimeters per second,
but because of the small dimensions involved the rate of change of velocity with distance
from the file is high
This results in the production of large hydrodynamic shear stresses around the file, which
are more than capable of disrupting most biological material
In a endosonic file the greatest shear stresses will be generated around points of
maximum displacement, such as the tip of the file and the antinodes along its length and
it is probable that will also be important in moving the associated irrigant around the canal
so that maximum benefit is achieved from the chemical irrigant
Although either type of endosonic instrument (sonic and ultrasonic) is capable of
producing acoustic micro streaming, the clinical efficiency of such forces will be
dependent upon the amount of file constraint that occurs – especially in tight or curved
canals.
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11. IRRIGANTS
The four goals of irrigation that one must take into account are lavage of debris, tissue
dissolution, antibacterial action and lubrication
Although preliminary debridement is accomplished with hand instruments irregularities
with debris and pulp tissue that current endodontic instrumentation could not be removed
One must therefore rely on lavage and some means of chemical dissolution of the
remaining tissue
Consequently, the ability of the irrigant to act as an effective organic solvent is of clinical
importance
This enhancing feature of the irrigant is one dimension of the improved physic chemistry
of irrigation within the multi dimensional endosonic system
There are several important aspects of irrigating root canals they use are the types or
irrigant used, the quantity of irrigant, temperature of the solution and its shelf life
The type of irrigant that should be used is agreed by most authorities to be Sodium
hypochlorite. It fulfils most of the requirements of an ideal irrigant by being bactericidal
and capable of dissolving organic debris
An agreement has not been reached on the optimum concentrations, although Martin and
Cunningham have recommend 2.5 per cent. Yet, it remains the most recommended
irrigant due to its synergistic effect with Endosonics.
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12. The phrase ‘copious irrigation’ is often found in the literature, yet this can be misleading,
as it is the quantity of irrigant that circulates to and from the apical limit of the root canal
that is important.
It has been found that with an irrigant flow of 20 ml per minute, it takes around 30
seconds for the irrigant to reach the most apical extent of the canal space.
Thus, an irrigant with solvent qualities used in large volumes and enhanced by ultrasonic
activation and mechanical energizing will be superior to conventional irrigant action
The temperature of the sodium hypochlorite is relevant because if it is heated from 21 to
37C its ability to dissolve collagen is enhanced
It has been pointed out that with continuous irrigation there is no heating effect in the
canal, therefore it may be of benefit to preheat the irrigant in the reservoir within the
endosonic unit
However sodium hypochlorite warmed to 37C remains stable for no longer than 4 hours
before breaking down
The shelf life of NaOCl varies with the concentration being employed
For example it has been found that the stable shelf life of 5.25% NaOCl is 10 weeks,
whereas 2.6% and 1.0% remain stable for only 1 week after mixing with water
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13. ULTRASONICS
Ultrasonic Endodontics is based on a system in which sound as an energy source (at 20
to 42 kHz), activates an endodontic file resulting in three dimensional activation of the file
in the surrounding medium
The ultrasonic systems (Magnetostrictive and Piezo-electric) involve a power source to
which an endodontic file is attached with a holder and an adapter
Ultrasonic handpieces use K-files as a canal instrument
Beginning at ISO size 15, they range upto size 40
Before a size 15 can fully function, however, the canal must be enlarged with hand
instruments to a size 20
Martin also designed a stiff, non-end cutting diamond file to be used in the straight part of
the canal
The irrigants are emitted from cords on the power source and travel down the file into the
canal to be energized by the vibrations.
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14. SONICS
The only similarity between the ultrasonic and sonic instruments is in imparting vibrational
type of movement for the root canal instrument, which they activate
The rest of the features such as the source of power, frequency of vibration, type of
handpiece and root canal instruments used are all different
Further more, unlike Ultrasonics, sonic system does not require special connections, as it
involves only a hand piece
Sonic instruments use compressed air line at a pressure of 0.4 MPa, which is already
available in the dental unit setup, as its source of power
There are two options for irrigating the root canal while using sonic handpieces
Either the water line of the dental units can be attached to the sonic handpiece, or the
water can be cut off and the dental assistant can introduce sodium hypochlorite from a
syringe
Sonic handpieces impart vibrations usually in the frequency of 1.5 – 3 kHz with provision
for adjusting the frequency, in the form a ring on the handpiece.
The root canal instruments which sonic handpieces use are specially designed and are
unique.
The three choices of files that are used with sonic handpieces are the Rispi sonic, Shaper
sonic and the Helio sonic
The Rispi sonic file resembles a rat-tail file and was developed by Dr.Retano Spinal
The Shaper sonic files were developed by Dr.J.M.Laurichesse and resemble a husky
barbed broach The Helio sonic file is otherwise known as Trio sonic or Triocut file and
resembles a triple helix Hedstrom file
All these instruments have safe ended non-cutting tip 1.5 – 2.0 mm in length
The ISO sizes of these instruments range from 15 to 40
As the graduated size instruments have varying shaft sizes, the instrument must be tuned
with the unit’s tuning ring to optimum tip amplitude of 0.5 mm.
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15. COMPARATIVE ANALYSIS
Shaping of Root Canals
High efficiency of Ultrasonics in dentin removal with reduced operator fatigue raised the
hope that it would be an ideal power driven device for root canal preparation
However, the results achieved by the ultrasonic units have ranged from outstanding to
disappointing
The explanation for such wide variance in results lies in the difficulty of controlling the
exact position of the tip and also the vibration of the file inside the canal curtails its hope
as a precise tool for root canal preparation, particularly the apical part
One of the uncharted problems with the ultrasonic units is their choice of enlarging
instrument – the K file
These files are made to function best in a push-pull, in and out motion
The action of the ultrasonic units, however, is an oscillating side-to-side, transverse
motion
Walmsley and Williams suggested that the devices would work much better if the
transverse motion could be changed to an up and down, longitudinal oscillation
May be rather than change the configuration of motion, the problem would be better
solved by changing thte canal instruments into a shape that functions better in an
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16. Ultrasonics will be of use in root canal preparations of its limitations and characteristics
are fully understood. Improper use of Ultrasonics may cause straightening or excessive
removal of the canal wall, ledging or perforation
In curved canals, only size 15 files can be used
Sizes 20 and above have been shown to cause straightening of the canal and apical
transportation
In the mesial roots of molars proper care should be shown as Ultrasonics may cause strip
perforations
It has been reported that many factors such as power setting, the interfacial force
between the file and dentin, direction of file oscillation, root canal geometry, type of
irrigant and the super imposition of operator assisted movement of the file may affect the
final shape of the preparation
Hence, using exclusively Ultrasonics for the preparation of root canal may not be a
predictable procedure
However, if used judiciously along with hand instruments, Ultrasonics may be a useful
adjunct for root canal preparations
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17. The unique oscillatory pattern of sonic files has made them a powerful root canal shaping
device
As with the ultrasonic canal preparations, these instruments must be free to oscillate in
the canal, to rasp away at the walls and to remove necrotic debris and pulp remnants
To accommodate the smallest instrument, size 15, the canal must be first hand
instrumented upto size 20
The sonic instruments, with their 1.5-2.0 mm safe tips, begin their rasping action this far
removed from the CDJ. This is known as the ‘Sonic Length’. As the instrument becomes
loose in the canal, the next size instrument is used thus developing a flaring preparation.
The Rispi sonic and the Shaper sonic files are more effective in canal shaping than the
Helio sonic
Bolanos et al found that the Shaper files left the least debris in the apical third and the
Rispi sonic the least in the middle and coronal thirds. Hence, it is recommended that the
Shaper sonic files be used first and that the remaining two thirds of the canal be finished
with the Rispi sonic.
The Sonics also cause least amount of straightening of canals when compared with the
Ultrasonics. The sonic technique also extrudes the least amount of apical debris when
canals merely irrigated during preparation and those canals prepared and then followed
by 3 minutes of ultrasonic instrumentation with a No.15 file and 5.25% NaOCl
The antibacterial efficacy of irrigants in Endosonics was further proved when the viable
counts of bacteria dramatically rerduced when water as an irrigant was replaced by
NaOCl.
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18. Root end Preparation
Although conventional endodontic therapy has been shown to be successful in 90% of
cases, a surgical approach is frequently indicated when a treatment through the canal is
not possible
Root end preparation and retrograde filing are commonly performed during endodontic
therapy when the quality of the apical sealing is doubtful
Thus, root end preparation is one of the most crucial factors in achieving success in
surgical endodontics
Recently, Ultrasonic retro preparation technique was devised to address the major
shortcomings of conventional rotary bur type of preparations
They are increasingly becoming popular and appear to have many advantages, such as
more conservative preparations, less need for beveling the root tip (decreasing the
chances of micro leakage), the the ability to prepare the canal farther in a coronal
direction from the apex with parallel walls for better retention
The dentin walls are also cleaner with less debris and smear layerThese special retro tips
are only 1/4mm in diameter, 3 mm in length, and about 1/10th the size of a conventional
micro head handpiece
Placing them in the long axis of the canal and then activating the ultrasonic unit use
them. It vibrates in the range of 30-40 kHz and a root-end cavity is prepared with parallel
walls 2.5 to 3 mm in depth
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19. Continuous irrigation cools the surface and maximizes cutting and debridement
Although Ultrasonics have made retro preparation of root apex simpler, easier and more
effective, long term clinical studies are warranted
Retro preparations tips specially designed for periapical surgeries are also available for
sonic handpieces
They are available in three standardized sizes (#35, #45, #55) and in two different lengths
(2mm, 3mm)
Although they are versatile in their angulations and can adapt to the various
configurations of the root apex, they are not very effective when compared to the
ultrasonic retro preparation tips.
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20. ENDODONTIC RE-TREATMENT
Intraradicular Post Removal
Teeth that present with intraradicular posts and periapical infections can be difficult to
retreat from a coronal approach
A traumatic and efficient post removal is essential for optimal non-surgical clinical
management.
Ultrasonics are highly efficient as post removal can be achieved with minimal loss of
tooth structure and decreased risk of other root damage
Ultrasonic instrumentation for post removal typically involves removing coronal cement
and build up material from around the post, then activating the tip of the ultrasonic
instrument against the metal post
The ultrasound energy transfers to the post and breaks down the surrounding cement
until the post loosens and is easily removed. Sonic instruments are ineffective at
removing cemented posts
It is possible that the frequency or amplitude of the vibrations play a key role in removing
the posts
Regardless of the method of sonic vibration, these instruments cannot be recommended
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21. Silver Point Removal
The tightly fitted, well cemented silver cone that is flush with the canal orifice is a
challenge to remove
In such cases, removal is enhanced through the use of ultrasonic devices
A conservative approach for removing defective silver points has been advocated by Krell
In this technique, a fine Hedstrom file is placed down into the canal alongside the silver
point
The file is then enervated by the ultrasonic tip and slowly withdrawn. A number of tries
are usually necessary before the silver point is loosened and retrieved.
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22. Gutta Percha Removal
Many endodontist believe that endodontic success depends more on what is taken out of
the canal (i.e. bacteria and necrotic tissue) than on what is put in it
The same is true for endodontic re-treatment. It is important to remove as much sealer
and gutta percha as possible in order to uncover remnants of necrotic tissue or bacteria,
which may be responsible for the endodontic failure
Ultrasonic instrumentation alone or with a solvent is as effective as hand instrumentation
in removing gutta percha from root canals
The ultrasonic-chloroform technique may produce residual slurry that may coat the canal
wall
In contrast, when halothane is employed it results in quick retrieval of the bulk of the filling
material and leave minimal residual debris
Although ultrasonic instrumentation require less time than hand instrumentation to attain
the working length, it uses significantly more solvent (chloroform or halothane) because
the solvent not only acts as an irrigant but also gets volatilized
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23. Sealer Placement & Gutta Percha Obturation
The significance of sealer consistency and placement has not been fully appreciated by
the practicing clinician
They constitute one of the most important variables, which determine the success of
Endodontic therapy
A novel method of sealer placement is by using an ultrasonic file – run without fluid
coolant, of course
A recent study found ultrasonic endodontic sealerplacement significantly superior to hand
reamer placement
They found the lateral and accessory canals well filled, with a proper coverage of the
sealer upto the apical orifice but not beyond
A common problem encountered with this technique is the “whipping up” of the cement in
the canal and causing it to set prematurely
This problem can be solved to an extent by replacing the ZnO-Eugenol sealer with a resin
sealer like AH-26
The Helio Sonic files are also equally useful for coating the canal wall with sealers and for
placing calcium hydroxide pastes
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24. Moreno’s Procedure
Moreno first suggested the technique of plasticizing gutta percha in the canal with an
ultrasonic instrument
His technique advocated the placement of gutta percha points to virtually fill the canal.
The attached endodontic instrument is then inserted into the mass and the ultrasonic
instrument is then activated
The gutta percha gets plasticized by the friction being generated
Final vertical compaction is done with hand or finger pluggers
A variation of this technique is in not attempting to plasticize the gutta percha
Ultrasonic energy is used only to condense the gutta percha mass with a spreader
This energized spreading technique leads to a more homogenous compaction of percha
with less stress and microleakage
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25. CONCLUSION
In an ultrasonic instrument the main driver oscillates in a true longitudinal manner, and as
it moves back and forth a transverse wave is generated along the length of the file with
the formation of a series of Nodes and Antinodes along the length of the file
However, in a sonic instrument a circular motion characterized by single antinodes at the
tip and a node near the driver is generated
The action of the driver imparts both a vertical and lateral component to the action of the
file
Thus, when the file is constrained within a root canal, this lateral component is essentially
eliminated, and a true vertical or longitudinal file movement remains
This difference is oscillatory pattern may explain the reportedly superior efficiency of the
sonic instrument during clinical usage
Contrary to earlier reports, it is highly unlikely that a confined area such as a root canal
would increase the probability of cavitation inception
Recent research has shown that the hydrodynamic shear stresses caused by the
acoustic streaming fields are responsible for many of the beneficial effects attributed to
the use of Endosonics
Irrigants play a crucial role in both short and long term success of endodontics through
their debriding and antimicrobial action. Sodium hypochlorite when activated with
Endosonics makes a potent synergistic combination for the efficient debridement of the
pulp space.
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