by Richman in 1957. The pioneer research on endosonics was done by Cunningham and Martin in early 1980. But these machines showed lots of problems like tip design of instrument was such that it could not be used along with sodium hypochlorite as an irrigant because machines used to get blocked due to crystallization of NaOCl in irrigation lines. Since then a lot of changes have been made in endosonics for example tip design has been specifically turned for endodontic use, etc (Fig. 12.54).
Fig. 12.54: Endosonic files
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Fig. 12.58: Acoustic streaming
2. Ultrasonic endodontics is based on a system on which sound as an energy source (at 20 to 42 kHz), activates an endo-dontic file resulting in three-dimensional activation of the file in the surrounding medium.
3. The ultrasonic systems involve a power source to which an endodontic file is attached with a holder and an adapter.
4. Ultrasonic handpiece uses K-file as a canal instrument (Fig. 12.55). Before a size 15 can fully function, the canal must be enlarged with hand instruments to a size 20.
5. The irrigants are emitted from cords on the power source and travel down the file into the canal to be energized by the vibrations (Fig. 12.56).
Advantages of Ultrasonics
• Clean canals free of smear layer and debris
• Enhanced action of NaOCl because of increased temperature and ultrasonic energy.
Type of Ultrasonics They are two types:
Magnetostrictive: It needs water coolant because it generates more heat. It is expensive, more clumpsy and less powerful.
Piezoelectric: Since, it generates less heat, it does not require water as coolant. It is used for location of calcified canals, retrieval of broken instrument and root-end preparation.
Mechanism of Action
Cavitation and Acoustic Streaming
Cavitation is defined as the growth and subsequent violent collapse of a small gas filled pre-existing inhomogeneity in the bulk fluid. This motion results in development of shock wave, increased temperature and pressure and free radical formation in the fluid (Fig. 12.57). Cavitation has been shown useful in removal of tooth deposits in scaling procedure but during its use in root canal regarding cavitation phenomenon, following points are to be considered:
• Threshold power setting at which this phenomenon occurs is beyond the range that is normally used for endodontic purpose.
• Cavitation depends on free displacement amplitude of the file. During root canal therapy, when file movement is restricted, this phenomenon is impossible to achieve.
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 (Fig. 12.58). This flow of liquid has 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 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 endodontic file the greatest shear stresses around the points of maximum displacement, such as the tip of file and the
Fig. 12.55: Diagrammatic representation of endosonic files
Fig. 12.56: Irrigants get energized with ultrasonic vibrations
Fig. 12.57: Cavitation
antinodes along its length in the canal, therefore it may be of benefit to preheat the irrigant in the reservoir within the endosonic unit.
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Uses of Endosonics Access Enhancement
Performing access preparation with burs can lead to gauging of the pulpal floor and sides of the chamber. But use of round or tapered ultrasonically activated diamond coated tips has shown to produce smooth shapes of access cavity (Fig. 12.59).
Orifice Location
Ultrasonic instruments are very useful in removal of the chamber calcifications as well as troughing for canals in isthmus and locating the canal orifices.
The troughing concept involves using an endodontic tip in back and forth brushing motion along a groove in the pulpal floor. By troughing there is better removal of tissue in the isthmus between the canals, and conservation of the tooth structure.
Irrigation
Studies have shown that use of endosonics have resulted in cleaner canals. There is a synergetic action of the physical action of the tip along with the chemical action of the sodium irrigant.
Acoustic streaming forces within the irrigant together with the oscillation of the instrument are useful for dislodging out the debris out of the canal.
Sealer Placement
One of the method of sealer placement is by using an ultrasonic file which runs without fluid coolant. A recent study found ultrasonic endodontic sealer placement significantly superior to hand reamer placement. 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.
Gutta-percha Obturation
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.
MTA Placement
MTA is a wonderful material with many uses. But its placement is difficult because of its sandy consistency. Low powered ultrasonics can be used to vibrate the material into position with no voids.
Endodontic Retreatment (Fig. 12.60) i. Intraradicular post removal
Teeth that present with intraradicular posts and periapical infections can be difficult to retreat from a coronal approach. Many techniques have been devised to aid in removal of posts from root canal spaces, of which 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 buildup 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.
Fig. 12.59: Diamond coated ultrasonic tips Fig. 12.60: Removal of post using ultrasonics
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Fig. 12.63: Hand spreader
ii. Gutta-percha removal
Studies have shown that ultrasonic instrumentation alone or with a solvent is as effective as hand instrumentation in removing gutta-percha from root canals. Although ultrasonic instrumentation requires 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.
iii. Silver point removal
A conservative approach for removing defective silver points has been suggested 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. Ultrasonics with copious water irrigation along with gentle up and down strokes is quite effective in not only removing silver points and broken files, but spreader and burs tips as well.
It is apparent that no automated device will answer all needs in cleaning and shaping. Hand instrumentation is essential to prepare and cleanse the apical canal, no matter which device, sonic and ultrasonic is used later. Both ultrasonics and sonics will be a useful adjunct in endodontics if their limitations and characteristics are fully understood.
INSTRUMENTS USED FOR