HYBRID TECHNIQUE

The Endodontic Glidepath: “Secret to Rotary Safety”

INTRODUCTION
You will do it 5,000 times in your career. Give or take a few…

The ADA estimates that most dentists treat an average of 2 endodontic teeth per week. If we assume there are at least 2 canals per tooth, 47 treatment weeks per year for 25 years, then most dentists will attempt approximately 5,000 Glidepaths in their career: 2 root canals per week x 2 canals per tooth x 47 weeks x 25 years = approximately 5,000 Glidepath attempts.
The amazing fact is that the subject of Glidepath has no formal training in the endodontic curricula of most dental schools. In fact, a PubMed Central search of Glidepath and endodontics reveals 300 references. However, none of them actually describe how to prepare a Glidepath. Most of the references say something like, “Of course you must first make a Glidepath.” That’s all. And so the purpose of this article is to serve as a reference guide for endodontic Glidepath preparation and answer the following questions: What is it? Why is it important? How do you predictably prepare the Glidepath?

Starting with the answer
The purpose of endodontics is to prevent or heal lesions of endodontic origin.1 In order to achieve this purpose, the root canal system must be successfully obturated. In order to be obturated, the root canal system has to be successfully 3-dimensionally (3-D) cleaned and rotary shaped. In order to be 3-D cleaned and rotary shaped, a Glidepath has to be successfully prepared (Figure 1). And so the Glidepath is the answer. It is the starting point of radicular preparations. Without it, cleaning and shaping become unpredictable or impossible because there is no guide for endodontic mechanics.
WHAT IS GLIDEPATH?
The endodontic Glidepath is a smooth radicular tunnel from canal orifice to physiologic terminus (foraminal constriction). Its minimal size should be a “super loose No. 10” endondontic file. The Glidepath must be discovered if already present in the endodontic anatomy or prepared if it is not present. The Glidepath can be short or long, narrow or wide, essentially straight or curved (Figure 2).

WHY IS THE ENDODONTIC GLIDEPATH IMPORTANT?
First, without the endodontic Glidepath, 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.”1 A nonsurgical seal requires first the creation of a radicular path that can be cleaned of viable and nonviable bacteria, vital and nonvital pulp tissue, biofilm, and smear layer; then shaped to a continuously tapering funnel that can be predictably and easily obturated.
Second, the Glidepath is necessary for quality control. Sustainable excellent endodontic obturations are not possible without it.

HOW DOES THE DENTIST PREDICTABLY PREPARE THE GLIDEPATH
In order to answer this question, I first surveyed the American Association of Endodontists (AAE) and reported my findings at the AAE annual scientific meeting in San Diego on April 16, 2010.2 The title of my presentation was “The Magic of Mastering the Glidepath: What Every Endodontist Should Know.” I asked the following 6 questions (Figure 3). The survey results speak for themselves.
What size hand file do you prefer for your Glidepath (Figure 4)?
Do you use straight manual files or do you curve them (Figure 5)?
Do you “go to length immediately” or do you do “early coronal enlargement” (Figure 6)?
When making the Glidepath, what is your preferred irrigating solution (Figure 7)?
How do you determine your Glidepath length (Figure 8)?
When making the Glidepath, what hand motion do you use (ie, “watch/wind,” “push/pull,” or other) (Figure 9)?

The fourth skill for consistent Glidepath preparation is to understand and master the 4 manual motions to prepare the rotary Glidepath.
1. “Follow.” Identify the entrance to the canal and remove any dentin or enamel triangles that are preventing straight-line access. Irrigate thoroughly with sodium hypochlorite before gently “slipping and sliding” down the canal (Figure 14). If a plug of dentin covers the orifices that have been identified using ultasonics, high-speed burs, or Mueller burs, first agitate chamber sodium hypochlorite using EndoActivator (DENTSPLY Tulsa Specialties). Then dense orifice dentin will be removed or softened, and small files can penetrate easily and the “following” motion can begin. Take the smallest file that fits the canal easily, and slightly precurve the apical a few millimeters using metal cotton pliers. If you are using a microscope, hold the handle of file with cotton pliers so your fingers do not block the line of sight to the orifice. Once the file can stand upright in the canal on its own, “follow” the file down the canal. Allow it to go whatever direction it wants. Be intentional about reaching the RT but stop attempting to “follow” short of maximum resistance and implement the No. 3 motion called “Envelope” (described below). When following to the RT, use watchwords such as gentle, caress, slip and slide, stroke, trail, and restraint. If RT is reached easily with the first “follow,” identified with apex locator and validated with radiographic or digital image, then proceed with manual motion No. 2: “Smooth.”

2. “Smooth.” Once RT file position has been validated, make short amplitude vertical stokes until the file is loose. This may mean a half a dozen strokes or it may mean 100 strokes. Whatever it takes, do it. If the file is at first too tight to easily make short strokes, ie, the file is apparently binding against 2 or more walls, then wiggle the handle left and right without any up or down motion. This simple, safe nuance will wear away the small amount of restrictive dentin and free the file for the smoothing motion. The minimal Glidepath file size for safe rotary shaping is a loose No. 10 file. While many endodontists prefer a larger file (55%, as noted in my spring AAE 2010 survey), every increase in size while making a theoretically bigger pilot hole for rotary, also risks creating a shelf in the radicular dentin wall. Rotary files rarely glance over shelves or ledges and must be meticulously removed before proceeding.4 An excellent series of manual files for smooth and progressive Glidepath enlargement are the ProFile Series 29 invented by Schilder (DENTSPLY Tulsa Specialties) (Figure 15).
3. “Envelope.” If the file does not easily “follow” to the RT, stop short of maximum resistance. You now have 2 choices: force or remove. If you force, you may block or ledge. So, DO NOT FORCE or PUSH. The proper 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 4 manual motions that removes dentin on the outstroke. The other 3 motions require that the file is moving in an apical motion in order to execute. This is a subtle motion and gives the impression that you are wasting your time because nothing is happening. But remember, endodontics is not a big job, it is a little job. The amount of tooth structure that is removed compared to coronal enamel and dentin preparations is minuscule. Endodontics is, however, a smart job. The “envelope motion” is a smart and efficient motion. Test it out yourself and experience that suddenly, effortlessly, and even miraculously the previous file “follows” deeper. You will experience a newfound freedom and control of the evolving radicular shape which, unfortunately, cannot be observed directly like all other restorative. Your unimpeded files are your eyes in endodontics. Now “follow” to the RT with your smallest file, smooth, and finish Glidepath. If you cannot “follow” to RT, you will almost always at least “follow” closer toward the RT. Envelope again and repeat until you reach RT, smooth, and finish the Glidepath.
4. “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. If you want to have a smooth No. 15 as your Glidepath size, for example, then use balance motion. It is safe and predictable. Originally this motion was referred to as Balanced Force or the Roane Technique, named after Dr. James Roane, the first person to describe this manual motion.6 Simply put, 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. During the clockwise motion, the file blades cut into the dentin; during the apical counterclockwise motion, the dentin is collected into the file’s flutes. This can be repeated several times as the file is “balanced” apically. The file is then turned clockwise and removed having carved a wider Glidepath. That same file is then used in a “smoothing” motion and the Glidepath is once again finished and ready for rotary shaping.
A new approach to increasing Glidepath size is mechanically vs. manually. One recent and successful method is the introduction of 3 PathFiles (DENTSPLY Tulsa Specialties) (Figure 16). When properly used, these robust and efficient rotary Glidepath files can take even further risk out of rotary shaping. As with every dental instrument, the dentist must precisely follow the manufacturer’s directions for use.

SUMMARY
The endodontic Glidepath is the secret to radicular rotary safety. This article has offered a definition of Glidepath, explained why it is important in producing optimum endodontic mechanics, and described how to prepare a Glidepath for radicular shaping. Four obstacles to Glidepath preparation have been identified along with the solution for each one. Four manual motions have been distinguished that, if used properly, will produce a safe rotary result and an endodontic experience that you truly control.

images for reference..

Properties of an Irrigant?
To effectively clean and disinfect the root canal system, an irrigant should be able to disinfect and penetrate dentin and
its tubules, offer long-term antibacterial effect (substantivity), remove the smear layer, and be nonantigenic, nontoxic
and noncarcinogenic. In addition, it should have no adverse effects on dentin or the sealing ability of filling materials.7
Furthermore, it should be relatively inexpensive, convenient to apply and cause no tooth discoloration.7 Other desirable
properties for an ideal irrigant include the ability to dissolve pulp tissue and inactivate endotoxins.13
What are the Types, Advantages and Disadvantages of Current Irrigants?
The irrigants that are currently used during cleaning and shaping can be divided into antibacterial and decalcifying
agents or their combinations. They include sodium hypochlorite (NaOCl), chlorhexidine, ethylenediaminetetraacetic
acid (EDTA), and a mixture of tetracycline, an acid and a detergent (MTAD).
Sodium Hypochlorite (NaOCl)
Sodium hypochlorite (household bleach) is the most commonly used root canal irrigant. It is an antiseptic and inexpensive
lubricant that has been used in dilutions ranging from 0.5% to 5.25%. Free chlorine in NaOCl dissolves vital and
necrotic tissue by breaking down proteins into amino acids.14 Decreasing the concentration of the solution reduces its
toxicity, antibacterial effect and ability to dissolve tissues.14 Increasing its volume or warming it increases its effectiveness
as a root canal irrigant.14
Advantages of NaOCl include its ability to dissolve organic substances present in the root canal system and its affordability.
The major disadvantages of this irrigant are its cytotoxicity when injected into periradicular tissues, foul
smell and taste, ability to bleach clothes and ability to cause corrosion of metal objects.15 In addition, it does not kill all
bacteria,12,16-18 nor does it remove all of the smear layer.19 It also alters the properties of dentin.20,21 The results of a recent
in vitro study show that the most effective irrigation regimen is 5.25% at 40 minutes, whereas irrigation with 1.3% and
2.5% NaOCl for this same time interval is ineffective in removing E. faecalis from infected dentin cylinders.22 Based on
the findings of this study, the authors recommend the use of other irrigants to increase the antibacterial effects during
cleaning and shaping of root canals.
Sodium hypochlorite is generally not utilized in its most active form in a clinical setting. For proper antimicrobial
activity, it must be prepared freshly just before its use.23,24 In the majority of cases, however, it is purchased in large
containers and stored at room temperature while being exposed to oxygen for
extended periods of time. Exposure of the solution to oxygen, room temperature
and light can inactivate it significantly.24
Extrusion of NaOCl into periapical tissues (Figures 5a and 5b) can cause
severe injury to the patient.25,26 To minimize NaOCl accidents, the irrigating
needle should be placed short of the working length, fit loosely in the canal
and the solution must be injected using a gentle flow rate. Constantly moving
the needle up and down during irrigation prevents wedging of the needle in
the canal and provides better irrigation. The use of irrigation tips with sideventing
reduces the possibility of forcing solutions into the periapical tissues.
Treatment of NaOCl accidents is palliative and consists of observation of the
patient as well as prescribing antibiotics and analgesics.
Chlorhexidine
Chlorhexidine gluconate has been used for the past 50 years for caries prevention,
27 in periodontal therapy and as an oral antiseptic mouthwash.28 It has a
broad-spectrum antibacterial action, sustained action and low toxicity.14 Because of these properties, it has also been recommended
as a potential root canal irrigant.14,27 The major advantages of chlorhexidine over NaOCl are its lower cytotoxicity
and lack of foul smell and bad taste. However, unlike NaOCl, it cannot dissolve organic substances and necrotic tissues present
in the root canal system. In addition, like NaOCl, it is unable to kill all bacteria and cannot remove the smear layer.29,30
Ethylenediaminetetraacetic Acid (EDTA)
Chelating agents such as ethylenediaminetetraacetic acid (EDTA), citric acid and tetracycline are used for removal of the
inorganic portion of the smear layer.7 NaOCl is an adjunct solution for removal of the remaining organic components. Irrigation
with 17% EDTA for one minute followed by a final rinse with NaOCl is the most commonly recommended method
to remove the smear layer.14 Longer exposures can cause excessive removal of both peritubular and intratubular dentin.31
EDTA has little or no antibacterial effect.32
MTAD
An alternative solution to EDTA for removing the smear layer is the use of BioPure™
MTAD™ (DENTSPLY Tulsa Dental Specialties, Tulsa, Okla.), a mixture of a tetracycline isomer,
an acid (citric acid) and a detergent.33 MTAD was developed as a final rinse to disinfect
the root canal system and remove the smear layer. The effectiveness of MTAD to completely
remove the smear layer (Figure 6) is enhanced when a low concentration of NaOCl (1.3%) is
used as an intracanal irrigant before placing 1 ml of MTAD in a canal for 5 minutes and rinsing
it with an additional 4 ml of MTAD as the final rinse.33 It appears to be superior to CHX in
antimicrobial activity.30 In addition, it has sustained antibacterial activity, is biocompatible and
enhances bond strength.14 Table 1 shows the advantages and disadvantages of current irrigants
utilized during root canal

The purpose of this article is to correlate the importance of irrigating with chelating agents (and their chemical reaction in eliminating the debris from between the flutes of separated nickel titanium files), with the ability to retrieve and/or bypass instruments separated within the root canal system.

Several methods and techniques have been advocated over the years for the removal of solid objects such as silver points and fragments of endodontic instruments that have been separated. If the coronal aspect of the fragment to be removed is accessible, it has the ability to be withdrawn from the canal by a variety of instrument systems. Examples of such systems include but are not limited to the Masseran™ Endodontic Kit (Micro-Mega, Lynnewood, Washington), the Cancellier Instrument Removal System™ (SybronEndo, Orange, CA) and the Ruddle IRS™ (Dentsply, Tulsa, OK). Recently, the use of piezoelectric ultrasonic units with their numerous compatible tips have facililated the incremental removal of dentin surrounding separated instruments as well as their vibratory removal. The use of a chelating agent will be shown to facilitate the removal and/or the dissolving of the debris trapped between the instrument flutes and the debris caught between the instrument itself and the dentinal wall.

Materials and Methods
The irrigation protocol used in this clinical study included the alternating use of a citric acid “50%” chelating solution, distilled water and chlorhexidine 0.12 or 0.2%.

One of the most important factors prior to instrument removal is the creation of a reservoir coronal to the separated fragment in order to receive the liquid.

This reservoir can be created with the use of modified gates glidden drills, #1 and #2 sectioned at their maximum cross-sectional to obtain a flat end and a predictable caliber (gg1=50, gg2=70), and an LA access bur (Sybron Endo) of appropriate size. The objective here is to create straight line access to the coronal aspect of the separated fragment for predictable removal as well as to provide a reservoir to hold an adequate volume of solution.

Sodium hypochlorite is probably the most widely used irrigant for root canal preparation.

For this procedure sodium hypochlorite is not recommended because this irrigant targets organic tissue and not the inorganic tissue that is meant to be demineralized in this situation. Citric acid has been recommended as a canal irrigant because of its ability to demineralize and to remove the smear layer6 which is thought to be mostly inorganic. Wayman et al.6 showed that 10,25, and 50% solutions of citric acid were all effective in removing calcium when used as a root canal irrigant. The demineralization effect of citric acid is apparently very rapid. Using dentinal discs, it has been shown that a 6% solution of citric acid required only 5s to remove much of the smear layer and exposed the orifices of the dentinal tubules. The distilled water is used to wash out the citric acid and the chlorhexidine acts as an antimicrobial agent.

The stropko™ Irrigator (Sybron Endo, Orange, CA) (Fig. 1) is also a very handy instrument to dry out the canal.

Once the reservoir has been created coronal to the separated fragment, a 50% solution of citric acid is used to fill it. The solution is brought in close contact with the fragment and the dentinal wall with a small caliber hand files such as a #06 or #08. The citric acid is then activated with a #15 ultrasonic file. This sequence is repeated frequently and small caliber precurved files are used in order to assure a good penetration of the irrigant and to try to create a path between the broken file and the dentine wall. This will allow the irrigant to be worked further apically and the fragment to be bypassed.
With the use of the dental operating microscope identification of the broken file separate from the dentinal wall and obturation material will become much clearer. Ultra sonic tips can be very useful in retrieving the separated instruments. The ultra sonic (piezoelectric) tips that are most useful are 4 Series (SybronEndo) consisting of three tips. The CT4 tip is the most robust tip and can be used at the highest levels, the UT4, a tip of medium thickness can be used at medium levels, and the SJ4, the finest tip, and should be used at the lowest power levels (Fig. 2).

The 4 Series tips are used in sequence a crown down manner from large size to medium size and then finally to small size. They should be introduced into the canal in contact with the broken file, activated for one or two minutes. They should be handled with a light touch and always kept in close contact with the exposed tip. Neither push pull movement nor excessive force should be applied as the objective is only to transmit vibration to the separated fragment so that it may be dislodged or further fragmented. This maneuver can be repeated several times, until the canal space is cleared. The first step is time-consuming and may need twenty to thirty minutes depending on canal configuration, canal length and position of the broken file. This technique is used in the straight coronal portion of the canal. If the separated fragment is located apical to the curve, and straight line access can’t be achieved then adequate vibrations can’t be delivered. In these cases, we often must be content by bypassing the separated instrument if it’s possible. The use of the dental operating microscope with fibreoptic illumination is very crucial for maximum predictability.

figures..

 The mechanical objectives for endodontic canal preparation were brilliantly outlined almost 40 years ago.¹ When properly performed, these mechanical objectives promote the biological objectives for shaping canals, 3-dimensional (3-D) cleaning, and filling root canal systems (Figure 1).² During the following decades there has been the emergence of a staggering number of file brands, sequences, and hybrid techniques advocated for shaping canals. However, recent advances for endodontic canal preparation have focused on the concept "less is more."³ This article will describe a single-file technique for shaping the vast majority of canals, regardless of their length, diameter, or curvature.

ROTATION VERSUS RECIPROCATION 
By far, the greatest number of commercially available files utilized to shape root canals are manufactured from nickel-titanium (Ni-Ti) and are mechanically driven in continuous rotation. On the other hand, reciprocation, defined as any repetitive back-and-forth motion, has been clinically utilized to drive stainless steel files since 1958. Initially, all reciprocating motors and related handpieces rotated files in large equal angles of 90° clockwise (CW) and counterclockwise (CCW) rotation. Over time, virtually all reciprocating systems in the marketplace began to utilize smaller, yet equal, angles of CW/CCW rotation. Today, the M4 (SybronEndo), Endo-Eze AET (Ultradent Products), and Endo-Express (Essential Dental Systems) are examples of reciprocating systems that utilize small, equal30° angles of CW/CCW rotation.

When shaping canals, it should be appreciated that there are both advantages and disadvantages associated with utilizing continuous rotating versus a reciprocating movement. The greater tactile touch and efficiency gained when continuously rotating Ni-Ti files in smaller-diameter and more curved canals must be balanced with the inherent risks associated with torque and cyclic fatigue failures. Fortunately, these risks have been virtually eliminated due to continuous improvement in file designs, Ni-Ti alloy, and emphasis on sequential glide path management (GPM).⁴ Compared to reciprocation, continuous rotation utilizing well-designed active Ni-Ti files requires less inward pressure and improves hauling capacity augering debris out of a canal.⁵

On the other hand, a mechanical reciprocating movement has merit because it somewhat mimics manual movement and reduces the various risks associated with continuously rotating a file through canal curvatures. However, current motors that drive reciprocating shaping files through equal forward and reverse angles generally require multifile sequences to adequately prepare a canal. Further, systems that utilize small, equal CW/CCW angles have recognized limitations, including decreased cutting efficiency, more required inward pressure, and a limited capacity to auger debris out of a canal.⁶ As such, there has been a genuine desire to rethink reciprocation and optimize the motors and files that utilize this concept. 

Serendipitously, in about 1998, Dr. Ben Johnson and Professor Pierre Machtou co-discovered the unmistakable advantages of reciprocating Ni-Ti files utilizing unequal bidirectional movements. Subsequently, in the late 1990s, Professor Machtou and his endodontic residents extensively analyzed this novel unequal reciprocating movement using the entire series of not-yet-to-market ProTaper files. Starting with the end in mind, Dr. Ghassan Yared, a former student of Professor Machtou, performed exhaustive work to identify the precise unequal CW/CCW angles that would enable a single reciprocating 25/08 ProTaper file to optimally shape virtually any canal.⁷ Although this specific reciprocation technique stimulated considerable interest, this file was never designed to be used in this manner. Yet, Dr. Yared’s work rekindled interest to take this single-file concept closer to its full potential.