Historically the glide path within the root canal system was enlarged with a series of hand files, but as hand files increase in size the stiffness also increases, thereby making procedural mishaps and ledge formation more likely. Hand files are also relatively inefficient requiring more chair-time to complete the procedure and may result in more postoperative discomfort as debris is expressed out the root apex.1 Mechanical nickel-titanium instruments have evolved to facilitate glide path management. However, until recently these instruments were designed to be used in combination with hand files adding more complexity to the root canal procedure. Hand instruments were used to scout the canal, while the rotary instruments would enhance the shape as a bridge to final instrumentation.
In the ongoing pursuit of predictability, ProTaper Ultimate (Dentsply Sirona) was launched late in 2021. This family of progressively tapered files is designed to create both a mechanical glide path and the final shape within the root canal system. (Fig. 1) Typical molar anatomy will require three or four files to complete all instrumentation. But, unlike previous file systems, the initial file is to be used as a glidepath instrument without the use of any hand files, increasing clinical efficiency.
The glidepath file, known as the Slider, has a tip diameter of 0.16mm and a taper in the apical three millimeters of 2% – the same taper as a traditional hand file. (Fig. 2) The file is manufactured out of M-wire2 and the cross section of the instrument changes from square at the tip to a parallelogram in the coronal half of the file. All files in the ProTaper Ultimate system rotate at 400 rpm. These design features have been incorporated into the Slider file and allow it to safely negotiate canals without the use of any hand instrumentation in most cases. If any hand filing is needed, it is generally minimal and confined to the apical few millimeters of the canal space.
For many practitioners the use of a rotary file prior to scouting with a hand file is considered taboo. This is the result of adhering to antiquated teaching methods and a lack of understanding about modern file design and metallurgy. The Slider design used with the correct cutting action results in a safe and predictable result. It is imperative that all cutting is done with the fluted portion of the file with light lateral pressure and no apical pressure or pushing of the file tip. Any engagement of the tip could lead to ledge formation or worse yet, file separation. However, the mean apical dimensions for root canal systems are significantly larger than the tip dimension of the Slider file, and therefore it should not be necessary to use the tip of the Slider instrument.3
Although the Slider tip is smaller than the apical constriction of the canal, the Slider file won’t always achieve working length. If apical resistance is met it is never wrong to use a #10 hand file to do more traditional instrumentation in the apical few millimeters to achieve apical patency. When in doubt, it is a more prudent choice to incorporate hand files into the procedure than to push the Slider file apically.
With the use of other clinical techniques, the necessity for hand files can be reduced even more. For example, removal of the dentin triangle just below the cementoenamel junction with an orifice opener prior to using the Slider will increase the coronal shape in the canal. This increased coronal shape creates mechanical advantage for the Slider and increases the likelihood the Slider will follow the canal space to the working length without any hand instrumentation. Obviously, this adds another instrument to the procedure, but doing so can result in a more efficient outcome.
Vortex orifice openers (Dentsply Sirona) provide a very effective way to remove the dentin triangle in premolar and molar teeth and they excel at centering the MB2 canal orifice over the body of the root in maxillary molars. (Fig. 3) Vortex orifice openers are active cutting rotary files that spin at 500 rpm. They are best used in a brushing motion out of the canal away from the furcation side of the root. These instruments have a short 11 mm handle to facilitate access into molar teeth in patients with limited opening. The cutting portion of the file is limited to 12 mm. The apical region of the file is tapered to provide access into the canal while the most coronal 4 mm of the file are parallel to prevent over enlargement of the canal.
If removal of the dentin triangle prior to glidepath enlargement doesn’t allow the Slider to reach working length, another alternative to hand filing would incorporate the second file in the ProTaper Ultimate system. The Shaper file will enhance the size of the canal in the midroot, coronal to the point of resistance for the Slider file. The Shaper has a tip diameter of 0.20 mm and a taper of 4% in the apical few millimeters of the file. (Fig. 4) The Shaper is fabricated from gold metal and like the other files in the ProTaper Ultimate system spins at 400 rpm. The Shaper has a maximum fluted dimension of 1.0 mm – identical to the Slider. It is important to limit the use of the Shaper to 1 mm less than the Slider length at this point of the procedure to prevent engaging the tip, which could create a ledge or result in file breakage. For example, if the estimated working length of the canal is 23 mm but the Slider meets resistance at 21 mm, using the Shaper file at 20 mm would enhance the canal shape coronal to the point of resistance for the Slider. This increased shape deeper into the canal will allow room for the Slider to advance past the initial point of resistance at 21 mm. By alternating the Slider and the Shaper (1 mm less than the Slider) these instruments will safely and incrementally advance to the apex without any hand instrumentation. After working length has been achieved with the Slider, the Shaper will follow at working length to further enhance the deep shape within the root canal system, allowing one or two of the finishing files to cut the final shape at root apex. This deep shape allows for debris removal and maximum disinfection of the root canal system prior to obturation.
A proper diagnosis, profound anesthesia, rubber dam isolation and access into the chamber are all needed prior to enlarging the glide path. Coronal access needs to be large enough to allow entry into all canals while preserving maximum tooth structure for restoration and function. In complex anatomies with small, long, and potentially multi-planar canals, it is not possible to immediately pass a 10 file to the root end, but this is not due to apical size.3 Many practitioners will attempt to force smaller files to the apex. However, # 6 and # 8 files are rarely needed to enlarge the glide path to the apex unless it is an extraordinarily difficult case. By removing the dentin triangle and alternating the use of the Slider and Shaper, not only can working length be achieved, but it can also be done without the use of any hand instrumentation in a safe and predictable manner.
The glide path does not need to be manufactured within the root canal system. It is pre-existing within the root. The glide path is nothing more than the natural space occupied by the one-time healthy dental pulp. Because of anatomical variability, especially in the apical one third of the root, the glide path may be irregular in many teeth and great care must be taken to follow the natural path of the canal. A proper glide path will allow rotary nickel titanium instruments to shape to the apical terminus of the root canal while minimizing the risk of instrument breakage.4 Fabricating a “white line” to the root apex by channeling through the root structure and creating a canal will not result in proper disinfection of the root canal system.
Endodontic success is dependent on a variety of interrelated factors, but removal of bacteria to treat apical periodontitis is the ultimate goal. A common misconception about root canal treatment is that the procedure somehow changes depending on anatomical complexity of the tooth, but this is not the case as the fundamentals remain constant. Obviously, some canals are more difficult to locate or negotiate and it is imperative that all canals are shaped to the root apex to achieve maximum disinfection. The key to success is to utilize simple and reproducible techniques early in the procedure to transform complicated root canal anatomies into predictably manageable cases, resulting in efficiency for both the clinician and patient.
- Coronal access needs to be large enough to uncover anatomy and facilitate cleaning of the canals but should also be as conservative as possible for restoration and resistance to fracture.
- Inadequate access and trying to force files apically are common causes for procedural mishaps.
- Never engage the tip of any file–hand or mechanical. All instrumentation must be done using the flutes of the file against the canal wall with lateral, not apical pressure.
- The glide path should be established in the presence of sodium hypochlorite to prevent blockage of small canals with pulp or dentin debris and to initiate the disinfection of necrotic teeth.
- Remove the dentin triangle with a Vortex orifice opener or the ProTaper Ultimate SX file.
- Alternate the Slider and Shaper (1 mm short of Slider) until working length is achieved.
- Canal anatomy at the apex can be irregular and care must be taken to follow the natural pre-existing glide path. It is never wrong to use hand files, but with new technologies it may no longer be necessary in the vast majority of cases.
1-3. 63-year-old female with necrotic tooth 1-4. Pulp chamber is constricted near the restoration, but canals are straight. The Slider was able to enlarge the glide path to the 23 mm working length with no hand instrumentation or orifice modification. The post-operative images reveal a lateral canal in the apical third of the root and the two canals joined at the apex to form a single space.
1&2. 42-year-old male with deep caries and symptomatic irreversible pulpitis tooth 1-7. A Vortex orifice opener (20.08) was used in the three main canals allowing the Slider to achieve the 22 mm working length without hand instrumentation. A #10 hand file was used to slightly enlarge the MB-2 canal prior to use of the Slider. The MB and MB-2 canals joined in the apical half of the root and microanatomy is apparent on the final obturation.
1&2. 56-year-old male with spontaneous pain and a necrotic pulp tooth 3-6. A Vortex orifice opener (20.08) was used to facilitate entry of the Slider. The Slider was able to achieve the 21 mm working length in the larger distal root. Alternating the Slider and Shaper was needed in the smaller mesial canals, but no hand instrumentation was required.
1&2. 17-year-old female with a previous pulp exposure tooth 3-6. With the larger canals no orifice modification or hand instrumentation was needed to follow the glide path. A SureFil SDR was placed over the chamber as a secondary orifice seal prior to temporization. The mesial canals join at the apex and a lateral canal is visible on the furcation side.
1-3. 39-year-old female with spontaneous pain and pressure symptoms from necrotic tooth 2-6. A Vortex orifice opener (20.08) was used in the three main spaces allowing the Slider to achieve working length in the DB and palatal roots. The Slider and Shaper were alternated to achieve working length in the MB canal. A #10 hand file was used to slightly enlarge the MB-2 canal orifice and the Slider was able to connect the MB-2 with the main MB space in the apical half of the root.
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- Pasqualini D, Mollo L, Scotti N, Cantatore G, Castellucci A, Migliaretti G, Berutti E. Postoperative Pain after Manual and Mechanical Glide Path: A Randomized Clinical Trial. J Endod 2012;38:32-6.
- Johnson E, Lloyd A, Kuttler S, Namerow K. Comparison between a novel nickel- titanium alloy and 508 nitinol on the cyclic fatigue life of ProFile 25/.04 rotary instruments. J Endod 2008;34:1406–9.
- Morfis A, Sylaras SN, Georgopoulou M, Kernani M, Prountzos F. Study of the apices of human permanent teeth with the use of a scanning electron microscope, Oral Surg Oral Med Oral Pathol 1994;77:172-6.
- Patino PV, Biedma BM, Liebana CR, Cantatore G, Bahillo JG. The influence of a manual glide path on the separation rate of NiTi rotary instruments. J Endod 2005;31:114–6.
About the Author
David Landwehr earned his D.D.S. at the University of Minnesota. He received an M.S. degree and certificate in oral and maxillofacial pathology at The Ohio State University, followed by specialty training in endodontics at the University of Michigan. Dr. Landwehr has been a private practice clinician for more than twenty years. Dr. Landwehr was the Chief of Endodontics for the Meriter Hospital general practice residency for over ten years. Dr. Landwehr authored the chapter “Lesions That Mimic Endodontic Pathosis” for the most recent edition of Cohen’s Pathways of the Pulp. His teachings focus on techniques used daily in his clinical practice that are efficient, predictable and evidence-based