|Year : 2016 | Volume
| Issue : 2 | Page : 32-37
What is a glide path?
Sachin Passi1, Nisha Kaler2, Nandini Passi3
1 Department of Conservative Dentistry and Endodontics, SriSukhmani Dental College and Hospital, Dera Bassi, Mohali, India
2 Department of Dentistry, Civil Hospital, Phase-6, Mohali (SAS Nagar), India
3 Department of Prosthodontics, SriSukhmani Dental College and Hospital, Dera Bassi, Mohali, Punjab, India
|Date of Web Publication||15-Mar-2017|
Civil Hospital, Phase-6, Mohali, Punjab
Source of Support: None, Conflict of Interest: None
Three-dimensional cleaning, shaping, and obturation of root canal system can be considered as foundations for a predictable endodontic success. One guiding strategy that has emerged as a critical part of endodontic success is the creation and maintenance of a glide path. Without it, cleaning and shaping become unpredictable because there is no guide for endodontic mechanics. Thus, a smooth glide path is the secret to safe and successful rotary shaping. However, this subject of glide path has no formal training in the endodontic curricula in most of the dental schools worldwide. The purpose of this review article is to serve as a reference guide for endodontic glide path preparation. Knowing what to do is only half of the job, implementing different skills in day-to-day clinical practice will accomplish the job fully, ensuring successful endodontic treatment outcomes.
Keywords: Glide path, physiologic terminus, radiographic terminus, rotary NiTi
|How to cite this article:|
Passi S, Kaler N, Passi N. What is a glide path?. Saint Int Dent J 2016;2:32-7
Over the four decades ago, Schilder outlined the principles of three-dimensional (3D) cleaning, shaping, and obturation of root canal system, which can be considered as foundations for predictable endodontic success. The preparation of root canal system remains one of the most difficult tasks in endodontic treatment due to the complex anatomy of root canals, with their irregular, noncircular cross-sections, multiplanar curves, bifurcations, trifurcations, lateral canals, accessory canals, apical ramification, fins, and cul-de-sacs. Further adding to this complexity, subsequent iatrogenic mishaps such as apical ledges, canal transportations, instrument separation, or the packing of dentinal debris, may further jeopardize the apical patency.
Thus, for a successful 3D obturation, root canal system has to be three dimensionally cleaned and shaped. One guiding strategy that has emerged as a critical part of endodontic success is the creation and maintenance of a glide path. Without it, cleaning and shaping become unpredictable because there is no guide for endodontic mechanics. The glide path confirms a sufficient existing space available for the next larger instrument for root canal preparation. Especially, when using rotary NiTi files, creation and maintenance of glide path are necessary because many available NiTi rotary instruments have nonend cutting tips  and because of their extreme flexibility, they cannot initially negotiate the root canals. Glide path also gives you an idea regarding the root canal curvature by carefully visualizing the file after it is withdrawn from the canal [Figure 1].
Glide path ultimately follows and replicates the original canal path to preserve position of nature's portal of exit location.
This subject of glide path has no formal training in the endodontic curricula in most of the dental schools worldwide. PubMed Central search of glide path and endodontics reveals more than 300 references. However, none of them actually describe how to prepare a glide path. Thus, the purpose of this review article is to serve as a reference guide for endodontic glide path preparation.
| What Is Glide Path?|| |
The endodontic glide path is a smooth radicular tunnel from canal orifice to physiologic terminus (foraminal constriction). Its minimal size should be a “super loose No. 10” endodontic file. The glide path must be discovered if already present in the endodontic anatomy or prepared if it is not present. The glide path can be short or long, narrow or wide, essentially straight or curved.
| Why Is the Endodontic Glide Path Important?|| |
First, without the endodontic glide path, the rationale of endodontics cannot be achieved. The rationale states that “any endodontically diseased tooth can be predictably saved if the root canal system can be nonsurgically or surgically sealed, the tooth is periodontally sound or can be made so, and the tooth is restorable.” A nonsurgical seal requires the creation of a radicular path that can be cleaned of viable and nonviable bacteria, vital and nonvital pulp tissue, biofilm, and smear layer and then shaped to a continuously tapering funnel that can be predictably and easily obturated.
Second, the glide path is necessary for quality control. Sustainable excellent endodontic obturations are not possible without it.
| Glide Path Controversy: Can We Do Without It?|| |
Initially, when rotary was introduced, clinicians believed in beginning the canal preparation directly with rotary instruments. However, now most of the researchers agreed that “getting to the apex” or “slipping and sliding to the physiologic terminus” represents the most important factor in root canal preparation. Creating a smooth glide path to physiologic terminus resembles a child riding down a slide in the park, randomly going down with the flow of the slide. Regardless of how efficient, safe, or simple system one is using, if a glide path is not present, mechanical files will eventually break. Blum et al. suggested that a glide path should be initially created with small flexible stainless steel hand files, to ensure that there will be sufficient space available for the rotary instrument to follow in the root canal. Berutti et al. recommended manual preflaring of the root canal to create a glide path before using NiTi rotary instrumentation and reported reduced torsional stress and increased the lifespan of rotary NiTi instruments. Patiño et al. also reported that the separation rate of the rotary NiTi instruments was significantly reduced when their use was preceded by glide path preparation. Undoubtedly, “crown-down” preparation technique or “pre-enlargement” or “preflaring” or “early coronal enlargement” allows removal of restrictive coronal dentin and provides a better access to the apical third part of the canal. Once the glide path has been created, this canal path is much more likely to be maintained with the larger instruments. Since most of the canals are large in young adults, a rotary instrument can safely follow to the physiologic terminus. As age increases, particularly if teeth are heavily restored, the rotary system may not even fit in the canal orifices. Scientific literature and clinical experience clearly show that successful outcomes will be more likely and iatrogenic mishaps will be minimal when instrumentation follows a designated route, a reproducible glide path.
| Glide Path Instruments and Preparation Technique|| |
While it is acknowledged that creating a reproducible glide path is essential, but an appropriate instrumentation is necessary to achieve the desired result. According to West, there are four skills that one should know to produce a consistent glide path:
- To find the canal - It is an important factor that one should address carefully before starting with the root canal preparation. Magnification and illumination are useful elements in locating the root canals
- To follow the canal to its radiographic terminus (RT) - Next important factor is to reach the RT. RT guarantees foraminal patency, which is prerequisite for a successful glide path
- Third important factor is to understand why one may not be able to easily follow to the RT. The four possible reasons responsible for this may include:
- Canal is blocked
- File curvature does not replicate canal curvature
- Diameter of file is too wide at its tip
- Diameter of file is too wide in its shaft.
- The fourth skill for consistent glide path preparation is to understand and master the four manual motions to prepare the rotary glide path.
- “Follow”- Identify the entrance to the canal and remove any restrictive dentin or enamel triangles that are preventing straight-line access. Irrigate thoroughly with sodium hypochlorite before gently “slipping and sliding” down the canal. Use the smallest file that fits the canal easily, and slightly precurves the apical few millimeters before insertion. Once the file can stand upright in the canal on its own, “follow” the file down the canal [Figure 2]
- ”Smooth” - Once the physiologic terminus has been reached, make short amplitude vertical stokes until the file is loose. If initially, the file is too tight to easily make short strokes, i.e. the file is apparently binding against two or more walls, then wiggle the handle left and right without any up or down motion. This simple motion will wear away the small amount of restrictive dentin and free the file for the smoothing motion, the minimal glide path file size for safe rotary shaping is a loose No. 10 file. If endodontists prefer a larger file, every increase in size will make a theoretically bigger pilot hole for rotary, thus risks of creating a shelf in the radicular dentin wall
- ”Envelope” - If the file does not easily “follow” to the physiologic terminus, stop short of maximum resistance. If one force, one might create a block or ledge. So, DO NOT FORCE or PUSH. The next step is to remove the file using the “envelope of motion.” The envelope will wear away restrictive dentin by withdrawing and carving to the right, or clockwise, direction. Envelope is the only motion of the four manual motions that removes dentin on the outstroke [Figure 3]. If one cannot “follow” to physiologic terminus, one should at least “follow” closer toward the physiologic terminus. Envelope again and repeat until physiologic terminus is reached
- ”Balance” – Sometimes, a file size larger than a super loose No. 10 is desired. The dentist may feel safer with a larger size, or the walls may not feel as smooth as possible, then balance motion is used. It is safe and predictable. Simply insert the instrument in the root canal, turn the handle of the file clockwise, and then turn it counterclockwise using slight apical pressure so that the file will not “unscrew” its way out of the canal. This can be repeated several times as the file is “balanced” apically. The file is then turned clockwise and removed after having carved a wider glide path.
Several authors have recommended using stainless steel K-files for preparing the glide path.,, There are several advantages for using stainless steel K-files as they have excellent tactile sensation and low potential for file separation. Very often the K-file has an impression of the canal when it is removed from the canal, thereby guiding the operator to the curvatures present in the canal. The stiffness of hand steel files also aids in negotiating blockages and calcifications. In 2006, West recommended using a K-file with an initial watch-winding motion to remove restricted dentin in very narrow canals, followed by a vertical in and out motion with a 1 mm amplitude and gradually increasing the amplitude as the dentin wall wears away and the file advances apically. However, it has also been observed that because of the relative stiffness of stainless steel files, there is a risk of canal transportation, which may lead to perforation, ledging, or apical zipping.,
In 2008, Kinsey and Mounce described a technique using a reciprocating handpiece attached to small size K-file for glide path preparation. The main advantages of using the reciprocating handpiece are to reduce glide path preparation time and hand fatigue as compared to the conventional manual technique. In this technique, initially canal patency is established with 8 or 10 K-file and working length is determined. Select the smallest size K-file that fits tightly into the root canal (say 8 K-file). Precurve the tip of the file and work the file down the canal up to working length using a “watch-wind” motion. Attach the M4 reciprocating handpiece (Kerr) to the handle of the file. While keeping the file at working length activate the handpiece. Let the handpiece “watch-wind,” the K-file for 5–10 s until the clinician feels that the file becomes loose in the root canal. Keeping the handpiece activated, withdraw the file approximately 0.5–1 mm from canal and move it back to length. If the file cannot be moved back to length, the handpiece must be removed and the file manually taken to length before proceeding. This process can be repeated until the file can be withdrawn and moved back to length over a distance of 3–3.5 mm. Repeat the procedure with 10 K-file and 15 K-file, withdraw the file 3–5 mm from working length. A successful glide path preparation is confirmed when the file can travel 5 mm in the root canal without any obstruction.
Recently, PathFile NiTi rotary files (Dentsply Maillefer) have also been introduced in the market for glide path enlargement. The system consists of three rotary instruments that can be used for glide path enlargement after initial negotiation and establishment of a glide path with a number 10 K-file., PathFile number 1 (purple) has an ISO 13 tip size, PathFile number 2 (white) has an ISO 16 tip size, and PathFile number 3 (yellow) has an ISO 19 tip size [Figure 4].
After a successful glide path has been established, PathFile No. 1 (0.13 mm) is introduced into the root canal at a rotation speed of 300 rpm in a delicate in and out movement until working length is reached (3–5 s). In canals that demonstrate accentuated curves in the apical third of the root canal system, it is also recommended to recapitulate with the size 10 K-file by hand to ensure complete patency of the root canal. PathFile No. 2 (0.16 mm) is then introduced followed by PathFile No. 3 (0.19 mm) following the same protocol.
The glide path can also be prepared using Xplorer instruments (Clinical Research Dental, London) rotating in an electric handpiece at 400 rpm [Figure 5]. The first instrument in this series is #15 file with a 0.01 taper.
When 0.02 taper instruments are used, then the transition from a #10 file to a #15 is often very difficult as there is a 50% increase in tip diameter. However, the Xplorer 15/0.01 is half the taper of a #15 hand file and has a triangular cross-section for added flexibility, so will glide down a canal, even with severe curvature, with relative ease if the #10 file has gone to length initially. If any resistance is encountered, the file should be withdrawn, and patency should be reestablished with a #10 file. The next file is the Xplorer 20/0.01 instrument with square cross-section, followed by a size 20/0.02 taper (also with square cross-section). One additional design feature is that there is a limited 10 mm cutting zone. This limits canal engagement and reduces instrument fatigue. Thus, it results in an efficient, predictable glide path to a size 20/0.02 taper.
MICRO-MEGA (France) has introduced two new rotary NiTi instruments, the G-Files™ [Figure 6]. The G-File™ NiTi instruments are machined into a narrow diameter (12 and 17) with a slight 0.03 taper. The superior cross-section of the G-File™ combines efficiency and safety. The G-File™ has cutting edges on three different radiuses, creating a large and efficient area for upward debris removal. The angular offset of the cutting edges also creates a different pitch along the length of the blade, avoiding any screwing or engaging effect into the walls of the canal. The nonworking (safety) tip is asymmetrical which helps the instrument safely move forward; this is also facilitated by the high degree of flexibility resulting from the small diameter.
The G-Files™ are electropolished, which improves their mechanical properties, particularly by releasing internal stresses which develop during machining, thereby increasing the flexibility of the G-File™. It also increases the efficiency in apical progression of the G-File™ while aiding in debris removal. The G-Files™ are available in 21, 25, and 29 mm.
Some clinicians also prefer Mtwo NiTi rotary instruments (Sweden and Martina, Padua, Italy: #10/04, #15/05, and #20/06) for the same purpose of creating an initial glide path mechanically. It has an S-shaped cross-section, a nonworking tip, a positive inclination angle, two cutting edges, and different tapers which prevent fracture and the transportation of debris toward the apex. Each instrument creates an access way for the next sequential instrument in the apical region, and all instruments are used till the working length. Plotino et al. (2006) concluded that the Mtwo rotary instruments might be used safely under clinical conditions in molars with severe curvatures.
Scout RaCe (engine-driven; FKG Dentaire, La Chaux-de-Fonds, Switzerland; #10 [0.02, 0.04], #15 [0.02], and #20 [0.02]) instruments are also used to prepare the glide path after initially scouting the canal with #8 stainless steel K-file. Ajuz et al. reported that NiTi instruments are suitable for adequate glide path preparation because they promoted less deviation from the original canal anatomy when compared with hand-operated instruments and also Scout RaCe showed an overall significantly better performance than PathFile (engine-driven; Dentsply Maillefer, Ballaigues, Switzerland).
| Manual Versus Mechanical Glide Path: “how Does One Choose”?|| |
Actually, the question should not be “manual verses mechanical” but rather “manual then mechanical.” Initially, one should always confirm the existence of a glide path manually. After establishing the glide path with a super loose No. 10 K-file, instead of using size 15/0.02 taper K-file and with a file tip 50% wider in diameter than a 10 K-file, other alternatives such as PathFiles and Xplorer files should be used. There is a significant possibility that size 15/0.02 taper K-file will not easily follow the size 10 K-file glide path and might result in ledging and apical transportation of the canal internally/externally. Schäfer et al. and Berutti et al. reported that when Mtwo and PathFile files were used without prior manual preflaring or coronal enlargement and were applied up to the working length, the initial files would come across greater friction in the canal, which could lead to a greater chance of instrument fracture.
| Postoperative Pain After Manual and Mechanical Glide Path|| |
The great elasticity of the NiTi alloy has permitted the increasing use of mechanical instruments for root canal shaping. NiTi instruments enable a more centered canal preparation with less transportation and incidence of canal aberrations. Instrumentation techniques involving a sort of rotational action usually cause less extrusion of debris than manual techniques with a linear filing movement. The amount of debris from the apical foramen produced with step-back technique instrumentation (2.58 mg) was greater than debris produced with other instrumentations such as NiTi rotary instrumentation (<0.50 mg). Thus, the glide path prepared with NiTi rotary instruments leads to less postoperative pain and faster symptom resolution.
| Conclusion|| |
West has rightly said “The endodontic Glide path is the secret to radicular rotary safety.” A confirmed and reproducible glide path is a prerequisite to rotary or reciprocal shaping. To be safe, before rotary shaping, the dentist must always discover manually whether a glide path already exists or needs to be created. The mechanized files will help in achieving this important step in endodontic procedure and provides the clinician with more confidence to prepare more complex and challenging endodontic cases. Knowing what to do is only half of the job, implementing these above-mentioned skills in day-to-day clinical practice will accomplish the job fully, ensuring successful endodontic treatment outcomes.
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Conflicts of interest
There are no conflicts of interest.
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