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Rotary NiTi instruments have revolutionised endodontics, allowing even the less experienced dentist to create perfectly truncated-conical shaping in harmony with the original anatomy. However, in clinical practice these instruments risk breaking if excessive strain accumulates. Strain is the result of two stresses: flexural stress and torsional stress^1-2. Flexural stresses are probably those most responsible for the breakage of rotary NiTi instruments and, as they are produced by the original anatomy of the root canal, the dentist can do little to reduce them^3-4.
If torsional stresses exceed the elastic limit of the NiTi alloy, they produce plastic deformation of the instrument, which immediately breaks². The dentist’s dexterity and the instrumentation technique used, are of primary importance in preventing the excessive accumulation of torsional stresses. Three main factors are responsible for torsional stresses: excessive pressure on the hand-piece⁵; excessive instrument blade-to-canal wall contact area^6-7. The third factor comes into play when the canal section is smaller than the tip of the instrument; this is inactive and thus incapable of cutting the dentine^6-7 and the result is known as “taper lock” and is followed by plastic deformation and instrument breakage⁸. This can be avoided by applying correct coronal enlargement^9-10 and appropriate pre-flaring. It aims to create a “glide path” before using any rotary NiTi instrument^11-12, thus the canal must be enlarged to the foramen to a diameter greater than or at least equal to the tip of the first rotary NiTi instrument that will be used^11-12. It is important to remember that all rotary NiTi instruments available on today’s market have inactive tips that are thus not capable of cutting dentine efficaciously.

Creation of the glide path is the last manual phase of the shaping sequence. It is the most difficult, especially for the general practitioner, and is the phase in which the most serious errors can occur, which; therefore, can cause the entire treatment to fail (steps, false paths, dentine plugs).

Fig 1: PathFile™ NiTi rotary instruments (DENTSPLY Maillefer). PathFile™ 1 (violet) tip, PathFile™ 2 (white) tip 16, PathFile™ 3 (yellow) tip 19. taper .02. Endodontic engine setting: 300 rpm, torque 5-6 N/cm.

The PathFile™ system comprises 3 rotary NiTi instruments, available in lengths 21, 25, and 31 mm (Fig. 1). The taper of all the instruments is .02 and the tip diameters are: PathFile™ 1 (violet) tip ISO 13, PathFile™ 2 (white) tip ISO 16, PathFile™ 3 (yellow) tip ISO 19.

The most significant features of these revolutionary new instruments are as follows:

Strength: the great strength is due to the square section and the very slight taper, only .02. The square section, which is easy to manufacture, has long been tested successfully for application to endodontic instruments, for example the K-files. The .02 taper ensures great resistance to cyclic fatigue, which is indispensable in the early phase of treatment when the canal curves are still virgin13, 14, 15, and 16.

Flexibility: flexibility is ensured by the NiTi alloy as well as by the taper of .02. This enables the original anatomy to be followed and maintained during the delicate phase of creating the glide path (Fig. 2). It also avoids the inexpert general practitioner having to use the rigid steel K-files that are frequently the source of errors, including irreparable ones such as steps, false paths, dentine plugs and transportation of the canal and of the apical foramen (Fig. 3, 4).

Fig 2: Endodontic treatment of tooth 16. The PathFilesT produce perfect pre-flaring in a few seconds, in harmony with the endodontic anatomy including in very difficult cases like this one.

Fig 3: Creating the glide path in the 2 mesio-vestibular canals of tooth 16 using steel K-files would have been very difficult, if not impossible. The risk of making irreparable errors such as steps, stripping, dentine plugs or foramen transportation is very high even for an expert endodontist, when tackling such difficult anatomy. The PathFiles™ were determinant in solving the case.

Safety: the working length is undoubtedly one of the most important aspects of the entire endodontic treatment. In the early phases the working length may change as the canal is enlarged and, in consequence, the radius of the curves is increased. The PathFiles™ are instruments that forgive these initial errors since they have the advantage of not creating steps if the working length is too short, and of not causing transportation of the foramen if the working length is too long (Fig. 5).

Fig. 5: Treating tooth 16 endodontically. Note the 90° curvature in the apical third of the disto-buccal canal is perfectly maintained. PathFilesT are at present the only instruments capable of creating the glide path in such complex anatomies rapidly and without risk because, before use, they only require the canal to be probed to the apex with a K-file # 08 or # 10.

Fig 4: Treating tooth 16 endodontically. In this case to the PathFiles™ were found to be determinant for success. 

Efficiency: the efficiency is given by the instrument’s four blades, which provide optimal cutting capability. This enables the PathFiles™ to be used at a speed of 300 rpm, and a very high torque value, in the range 5-6 Ncm (maximum torque available with the X-Smart™ endodontic engine, DENTSPLY Maillefer).

Simplicity of use: the enormous advantage that the PathFiles™ possess is that they only require the dentist to probe the canal to the foramen with a #10 K-file before use. It is intuitively obvious that with such a thin and flexible hand instrument it will almost always be possible to reach the end of the canal without difficulty. Even the least expert general practitioner can thus eliminate the last manual phase, in which training and skill in using endodontic instruments is fundamental to avoid errors which can be irreparable (Fig. 6, 7). The PathFiles™ will provide the expert endodontist with trusty friends capable of transforming a complex endodontic anatomy into a simple case that can be treated almost entirely with rotary NiTi instruments.

Fig. 6: Treating tooth 27 endodontically. The double curvature of the mesio-vestibular canal was perfectly conserved.

Fig. 7: Treating teeth 26 and 27 endodontically. The use of hand stainless steel K-files up to # 20 to create the glide path in such complex anatomies carried a risk of altering the original anatomy that could have serious consequences. On the contrary, in a few seconds Pathfiles™ have prepared the canal for the subsequent rotary NiTi instruments that, with their increased taper, completed the shaping.

The PathFiles™ were subjected to trials to evaluate their efficacy as soon as they become available. The research by Berutti, Cantatore, Castellucci and co-workers, recently published in the Journal of Endodontics17 is one such significant study. The study compared changes to canal curvature and incidence of canal aberrations after preflaring with hand K-files or with nickel-titanium rotary PathFiles™, in S-shape Endo Training Blocks. The influence of the operator’s expertise was also investigated. One hundred training blocks were coloured with ink and pre-instrumentation images were acquired digitally. Preflaring was performed by an endodontist with PathFile (group 1) and with hand stainless steel K-files #10-15-20 (group 2); an inexpert clinician performed preflaring with PathFile (group 3) and with hand stainless steel K-files (group 4). Pre-instrumentation and post-instrumentation images were superimposed to evaluate the outcomes investigated (Fig. 8).

Fig. 8: Superimposition of pre-instrumentation and post-instrumentation images (plastic blocks). (A) Group 1, PathFile™/expert; (B) Group 2 K-files/expert; (C) Group 3, PathFile™/inexpert; (D) Group 4 K-files/inexpert.

The mean radius of curvature pre- and post-instrumentation for each sample was measured. The variation of the radius of curvature is a significant parameter to verify the instrumentation’s ability to maintain the original anatomy. To avoid measurement mistakes, the percentage of increase between pre- and post-instrumentation radii was calculated. A high percentage means a significant alteration of the original anatomy, whereas a low percentage means a shape in harmony with the original anatomy.

Differences in canal curvature modification and incidence of canal aberration were analysed with the Kruskall-Wallis plus post hoc tests and by the Monte Carlo method, respectively (P < .05). The PathFile™ groups demonstrated significantly less modification of curvature (P < .001) and fewer canal aberrations (P < .001). No expertise-related difference was found within instrument groups (P > .05), whereas the inexpert clinician produced more conservative shaping with Pathfiles™ than did the expert with manual preflaring (P < .01).

Fig. 9: Percentage variations of the apical and coronal radii. Using PathFiles™ an inexpert operator can maintain the original anatomy better than an expert operator using hand stainless steel K-files.

Fig. 10: Penetration of the radiopaque irrigant into the canals of two mandibular molars after probing with a K-file 10 (left) and with a PathFile™ 1 (right). After the PathFile™ 1 the irrigant has already reached the apical third of all the canals.

At the last National Congress of the S.I.E. (Italian Endodontics Society) which was held in Turin, Italy on 13-15 Nov. 2008, Greco and Cantatore presented an interesting study that evaluated in vitro “the difference in penetration ability of radiopaque irrigant solutions between a pre-flaring method with conventional hand stainless steel instruments (steel K-files # 10, 15 and 20) and rotary instruments in NiTi (PathFiles™)”¹⁸. The results showed a statistically-significant difference in the penetration of the irrigant in the middle and apical thirds of the canal using the first two PathFiles™ compared to manual instrumentation with steel K-files # 10 and 15. The significance disappeared with the last and largest instruments: PathFile™ 3 and steel K-file # 20. The authors of the study concluded that mechanical pre-flaring would appear to facilitate the flow of the irrigant solution compared to the use of hand stainless steel K-files. This research throws light on a new characteristic of the PathFiles™: their ability to remove the content of the root canal together with the detritus produced while working. This highly important characteristic is common to all rotary NiTi instruments and is also responsible for the almost complete lack of extrusion of detritus beyond the apex while using the PathFiles. It should be remembered that the PathFiles™ are used after having probed the canal only with a K-file # 10. With this hand file it is almost impossible to create periapical problems.
By eliminating this last manual phase, using the PathFiles™ to create the glide path, post-operative pain can also be reduced. Thus two goals are achieved: greater comfort for the patient and the possibility of performing treatment in a single session, which has been shown to carry a higher success rate¹⁹. In this connection, Berutti, Castellucci, Cantatore and co-workers have begun a study to verify the incidence of post-operative pain in patients after the glide path has been created with PathFiles™ vs. manual stainless steel K-files. Statistical significance has not yet been achieved, probably because the series is still very small at this early stage of the study, but the trend is towards a lower incidence of post-operative pain in patients in whom the PathFiles™ are used.²⁰

It may be concluded that PathFiles™, the new rotary NiTi instruments, open up a new era in the instrumentation of root canals enabling the glide path to be created easily and safely including by the less expert general practitioner. They are also a valid help to the expert endodontist who, by using PathFiles™, can easily treat even a complex canal anatomy.

Abstract

Rotary NiTi instruments have revolutionised endodontics, enabling even the less expert dentist to perfectly and speedily shape the root canal in harmony with the original anatomy. All the NiTi rotary systems available today consist of instruments whose tips are relatively inactive, a design feature whose aim is to avoid drawbacks such as steps, false paths or foramen transportation. Thus an initial manual phase is indispensable to enlarge the canal at least to the size of the tip of the first rotary NiTi instrument that will be used. This pre-flaring is fundamental to avoid torsional breakage of the rotary NiTi instruments. This last manual phase, for which stainless steel K-files are used, is the most difficult and delicate stage of the entire treatment and one in which errors, sometime irreparable ones, can easily be made.
The new rotary NiTi instruments PathFile (DENTSPLY Maillefer) have been designed so that pre-flaring can be achieved in a few seconds and in absolute safety, creating the so-called glide path, before using any type of rotary NiTi system. The PathFile system consists of three rotary NiTi instruments with the following characteristics:
taper: .02
lengths available: 21, 25, 31 mm
PathFile 1 (violet) tip 13
PathFile 2 (white) tip 16
PathFile 3 (yellow) tip 19
endodontic engine setting: 300 rpm. torque range: 5-6 N/cm
Before using the PathFiles it is only necessary to check that the canal is passable with a K-file # 08 or # 10. Clearly with thin hand instruments such as a K-file # 10 it is impossible even for the least expert dentist to make mistakes.

For more information of Pathfiles™, or to place an order, please contact your local DENTSPLY dealer or representative on +44 (0) 1932 853422.

*Berutti Elio MD DDS: Full Professor of Endodontics, Turin University, Italy 00390114346846 E-mail elioberu@tin.it

**Cantatore Giuseppe MD DDS: Associate Professor of Endodontics, Verona University, Italy 0039065135082 E-mail cantatore@mac.com

***Castellucci Arnaldo MD DDS: Contract Professor of Endodontics, Florence University, Italy, 0039055577400 E-mail castellucci@dada.it

References

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