Scoutrace

Scoutrace Files

• ScoutRace is a sequence of three instruments with .02 taper and with ISO sizes of 10, 15 and 20
• These are used at 600–800 rpm
• These have extreme flexibility due to 0.02 taper, rounded safety tip for precise guiding, alternating cutting edges to avoid screwing-in effect, sharp edges for best cutting efficiency, and electrochemical polishing for better resistance to torsion and fatigue

Read And Learn More: Endodontics Notes

Group 4 Sonics And Ultrasonics In Endodontics

The ultrasonic instrument was first used in dentistry for tooth preparation with an abrasive slurry. Though it showed low cutting effiency, it had many advantages like improved visualization, a conservative approach, and selective cutting. The concept of using ultrasonics in endodontics was suggested by Richman in 1957.

The pioneering research on endodontics was done by Cunningham and Martin in early 1980. Endodontics is a device which imparts sinusoidal vibration of high intensity to a root canal instrument.

Sonic Handpiece

• Sonic instruments rely on a passage of pressurized air through the instrument handpiece for use operating at 3–6 kHz. Its handpiece is attached to a normal airline, so it uses compressed airline at a pressure of 0.4 MPa (already available in dental unit setup as its source of power)
• It has an adjustable ring to give an oscillating range of 1,500–3,000 cps
• There are two options for irrigating the root canal while using sonic handpieces. Either the waterline of the dental units can be attached to the sonic handpiece or the water can be cut of and the dental assistant can introduce
• sodium hypochlorite from a syringe:
• Sonic handpiece uses the following types of files:
  • Helio sonic (Trio sonic)
  • Shaper sonic
  • Rispi sonic
• All these instruments have safe-ended noncutting tip 1.5–2 mm in length. The sizes for these instruments range from 15 to 40
• The instrument oscillates outside the canal which is converted into vibrational up-and-down movement in the root canal. Sonic instruments are used in step down technique
• To permit the insertion of No. 15 sonic fie, the canal should be initially prepared with conventional hand fies (No. 20). Sonic fie begins its rasping action 1.5–2.0 mm from the apical stop. This length is called as sonic length
• When sonic fie is operated without any constraint, it sets up circular motion characterized by true vertical or longitudinal movement.

Advantages of Sonic Instruments:

• Better shaping of the canal as compared to ultrasonic preparation
• Due to constant irrigation, lesser chances of debris extrusion beyond the apex
• Produces clean canals free of smear layer and debris

Disadvantages of Sonic Instruments:

• Walls of prepared canals are rough
• The chances of transportation are more in curved canals.

Ultrasonic Handpiece:

• Ultrasonic endodontics is based on a system in which sound as an energy source (20–42 kHz) causes three-dimensional activation of a file in the surrounding medium. Ultrasound energy can be produced by magnetostriction; it converts electromagnetic energy into mechanical energy or piezoelectricity principle.
• In this, crystal is used which changes dimension when an electric charge is applied, therefore, the electric current generates a wave in the crystals. This crystal deformation is converted to mechanical oscillation with no production of heat
• Ultrasonic systems involve a power source to which an endodontic fie (K file) is attached with a holder and an adapter. Before a size 15 can be freely used with ultrasonics, the canal must be enlarged with hand instruments to a size Nos. 30–40 fie Irrigants are emitted from cords on the power source and travel down the file into the canal to be energized by the vibrations

Advantages of Ultrasonics:

• Clean canals free of smear layer and debris
• Enhanced action of NaOCl because of increased temperature and ultrasonic energy.

The disadvantage of Ultrasonics:

Causes transportation of root canal if used carelessly.

Mechanism of Action/Biophysics:

• Cavitation

Cavitation is defined as the growth and subsequent violent collapse of a small gas field with pre-existing inhomogeneity in the bulk fluid. When a vibrating object is immersed in a fluid, oscillations cause a local increase (compression) or decrease (rarefaction) in fluid pressure. During the rarefaction phase, at a certain pressure amplitude, the liquid fails under acoustic stress and form cavitation bubbles.

During the next positive pressure phase, these vapor-filled cavities implosively collapse resulting in shock waves. Cavitation has been shown useful in the removal of deposits in scaling procedure, but during its use in root canal regarding the cavitation phenomenon, the following points are to be considered:

• • The threshold power setting at which this phenomenon occurs is beyond the range that is normally used for the endodontic purpose
  • Cavitation depends on the free displacement amplitude of the fie. During root canal therapy, when fie 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. This flow of the 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 stress around the fire, which are more than capable of disrupting most biological material.

Uses of Endodontics:

Access enhancement:

The use of round or tapered ultrasonically activated diamond-coated tips has been shown to produce smoother shapes of access cavities.

Orifie location:

Ultrasonic instruments are very useful for the removal of chamber calcifications, troughing for canals in the isthmus, and locating the canal orifices.

Irrigation:

Endosonics results in the activation of the irrigating solution in the canal by cavitation and acoustic streaming. This combined with the oscillation of the instrument results in cleaner canals.

Sealer placement:

Sealer is placed using an ultrasonic fie which runs without fluid coolant.

Gutta-percha obturation:

Moreno first suggested the technique of plasticizing gutta-percha in the canal with endodontics. Gutta-percha gets plasticized due to friction being generated. Final vertical compaction is done with hand or finger pluggers.

MTA (Mineral Trioxide Aggregate) placement:

Low-powered ultrasonics can be used to vibrate the material into position with no voids.

Endodontic retreatment:

• Intraradicular postremoval:

Ultrasonics help in the removal of the post by activating tip of the ultrasonic instrument against the metal post. The ultrasound energy transfers to the post and breaks down the luting cement resulting in the loosening of the post

• Gutta-percha removal:

Endosonics alone or with solvent helps in removing gutta-percha from canals

• Silverpoint removal:

Krell introduced a conservative approach for the removal of silver points. In this, a fie H-fie is placed into the canal alongside the silver point. The file is then activated by the ultrasonic tip and slowly withdrawn. Ultrasonics with copious irrigation along with gentle up and down strokes is quite effctive in the removal of silver points, separated files, burs tips, etc.

Instrument Deformation And Breakage

An unfortunate thing about NiTi instruments is that their breakage can occur without any visible sign of unwinding or permanent deformation, that is, visual examination is not a reliable method for evaluation of any NiTi instrument. There are two modes of rotary instrument separation, namely, torsional fracture and flexural fracture.

Torsional Fracture:

A torsional fracture occurs when the torque limit is exceeded. Term torque is used for forces which act in a rotational manner. According to Marzouk, torque is the ability of the handpiece to withstand lateral pressure on a revolving tool without reducing its speed or cutting effiency. The amount of torque is related to the mass of the instrument, canal radius, and apical force when worked in the canal.

As the instrument moves apically, the torque increases because of the increased contact area between the fie and canal wall. Theoretically, an instrument used with high torque is very active, but the chances of deformation and separation increase with high torque. Thus, as the fie advances further into the canal, pressure should be reduced to decrease torque.

Depending on the manufacturer and condition of the handpiece, each handpiece has a different degree of effctiveness depending upon the torque values.

Role of Handpiece:

Handpiece is a device for holding instruments, transmitting power to them, and positioning them intraorally. Both speed and torque in a handpiece can be modified by the incorporation of a gear system. Various types of gear systems can be incorporated in the handpiece but the gearing is limited by the need to maintain the drive concentrically through the handpiece and the head.

Torque control motors allow the setting of torque produced by the motor. In low torque control motors, torque values set on the motor are less than the value of torque at the deformation and separation of the instruments. Whereas in high torque motors, torque value is higher as compared to torque at deformation and separation of the rotary instruments.

During root canal preparation, all the instruments are subjected to different levels of torque. If the torque level is equal or greater than the torque at deformation, the instrument will deform or separate. Thus, with low torque control motors, the motor will stop rotating and may even reverse the direction of rotation when the instrument is subjected to a torque level equal to the torque value set at the motor.

By this, instrument failure can be avoided. In high-torque motors, instruments may deform or separate before the torque value of the motor is achieved. So, we can say that torque control is an important factor to reduce NiTi fracture.

Flexural Fracture:

When an instrument rotates in a curve, it gets compressed on the inner side of a curve and stretched on the outer side of the curve. With every 180° of rotation, the instrument flexes and stretches again and again resulting in cyclic fatigue and subsequent fracture of the instrument.

In large-size fields because of more metal mass, more of tensile and compressive forces occur resulting in early fatigue of the instrument. Elastic and fracture limits of NiTi rotary instruments are dependent on the design, size, and taper of the instrument. This to prevent instrument deformation and fracture, the right torque value for each instrument should be calculated.

Sotokowa’s classification of instrument damage:

• Type 1: Bent instrument
• Type 2: Straightening of twisted flutes
• Type 3: Peeling of metal at blade edges
• Type 4: Clockwise twist (partial)
• Type 5: Cracking of instrument along its long axis
• Type 6: Full fracture of instrument

Prevention of Breakage of Instruments when using Nickel–Titanium Rotary Instruments

• Use only torque-controlled electric handpieces for rotary instruments
• A proper glide path must be established before using rotary files, that is, getting the canal to at least size 15 before using them
• Use crown down method for canal preparation. By this apical curves can be negotiated safely
• Frequent cleaning of flies should be done as it reduces the chances that debris will enter the microfractures and result in the propagation of the original fracture and finally the separation
• Do not force the file apically against resistance. The file should be moved smoothly with 1–2 mm deep increments relative to the previous instrument
• Canals should be well lubricated and irrigated to reduce friction between the instrument and dentinal walls
• Dentin mud collected in the canal increases the risk of fracture, it should be cleared of by frequent irrigation
• Discard a fie if it is bent, stretched, or has a shiny spot
• Do not use rotary nickel–titanium files to true working length especially in teeth with S-shaped canals, canals with multiple and sharp curves, and if there is difficult access of orifice because it can place stresses on the instrument which will cross the breaking torque value. In such cases, the apical portion of the canal should be prepared by hand fies
• A fie should be considered disposable when
  • It has been used in curved canals
  • Despite an excellent glide path, it does not cut dentin properly

Two things can be done to reduce the risk of NiTi fracture:

1. Examine the file every time before placing it into the canal
2. Bend the file to at least an 80° angle, every time before placing it into the canal, to see if it will fracture

Instruments Used For Filling Root Canals

Spreaders and pluggers are used to compact the guttapercha into the root canal during obturation. In 1990, ISO/ADA Endodontic Standardization Committee recommended the size of 15–45 for spreaders and 15–140 for pluggers.

Hand Spreader:

• It is made from stainless steel and is designed to facilitate the placement of accessory gutta-percha points around the master cone during the lateral compaction technique
• Hand spreader does not have a standardized size and shape
• It is not used routinely because excessive pressure may cause a fracture of the root.

Finger Spreader

• They are shorter in length which allows them to afford a great degree of tactile sense and allows them to rotate freely around their axis
• They are standardized and color-coded to match the size of gutta-percha points
• They can be manufactured from stainless steel or nickel-titanium
• Stainless steel spreaders may pose difficulty in penetration in curved canals and may cause wedging and root fracture if forced during compaction. They also produce great stress while compaction
• NiTi spreaders are recently introduced spreaders which can penetrate curved canals and produce less stress during compaction. But they may bend under pressure during compaction.
• So, we can say that combination of both types of spreaders, that is, stainless steel and NiTi, is recommended for compaction of gutta-percha, NiTi spreaders in the apical area and stainless steel in the coronal part of the root canal

Hand Plugger:

• The hand plugger has a diameter larger than the spreader and have a blunt end
• It is used to compact the warm gutta-percha vertically and laterally into the root canal
• It is also be used to carry small segments of gutta-percha into the canal during the sectional filing technique
• Calcium hydroxide or MTA-like materials may also be packed into the canals using a hand plugger

Finger Pluggers :

They are used for vertical compaction of gutta-percha. They apply controlled pressure while compaction and have more tactile sensitivity than hand pluggers. Care should be taken with spreaders and pluggers while compacting the gutta-percha in canals.

They should be cleaned prior to their insertion into the canal; otherwise, the set sealer from the previous insertion may roughen their surface and may pull the cone outside the canal rather than packing it. Also, one should discard the instrument when it has become bent or screwed to avoid instrument separation while compaction.

Lentulo Spiral

• Lentulo spirals are used for applying sealer to the root canal walls before obturation
• Available in lengths of 17, 21, and 25 mm
• It has left-handed screw threading so that the sealer flows down to the tip when rotated in low speed.

Endodontic Instruments Conclusion

Since ages, many areas offer many exciting research possibilities to further increase the performance of endodontic instruments by increasing flexibility, bending, and torsional strength of files without compromising the cutting efficiency.

In the case of rotary NiTi instruments, the use of the right speed and torque are stressed for controlled instrumentation. One should not use rotary NiTi files overenthusiastically without a complete understanding of the physical and mechanical properties of NiTi instruments.