The Endodontic Glidepath: “Secret to Rotary Safety”

GLIDEPATH TECHNIQUE
There are 4 skills that you need to know in order to produce consistent Glidepaths for safe rotary. First, find the canal. When beginning an endodontic procedure, it is useful to know the number of canals typical to a particular tooth. It is also useful to know the typical anatomic variations of the specific tooth you have scheduled to treat (ehuman.com/products/3d-tooth-atlas-6). When reviewing ToothAtlas teeth, the first realization is the typical root canal system anatomy of a specific tooth is not typical at all. None are the same and that is the lesson: always expect the unexpected; no 2 root canal systems are the same—root canal systems are literally like “banners in the breeze.” They are complicated and curved, their canal walls vary from smooth to rough, from wide to narrow, or from patent to clogged with pulp, necrotic debris, or calcifications. Once you know the typical number of canals for a particular tooth and you understand some of the anatomical possibilities, then magnification and illumination are essential to finding canals. Any dentist serious about endodontic treatment should be trained in the use of the operating microscope. With an aging population and therefore aging teeth with their root canal systems, normal calcific degeneration occurs and when these pulps become nonvital, the canals are smaller and more difficult to find without magnification and illumination (Figure 10).
Second, “follow” the canal to its radiographic terminus (RT). While the RT is always some distance past the physiologic terminus, the RT is the best default or home base position (Figure 11). By “following” to the RT, the clinician guarantees foraminal patency, which is prerequisite for a successful Glidepath. The technique is to clean to the RT and then shape inside using a wide variety of physiologic terminus location methods such as apex locator, paper point determination, different angle radiographs or digital images, and, finally, patient response to an endodontic file passing through the foraminal constriction where a lesion of endodontic origin exists and anesthesia is not being used or wearing off at the end of a visit.

Figure 10. Severely calcified canal (left) can be successfully “followed” using microscope and color differentiations. Note canal patency (right) did not occur until a few millimeters from the canal terminus and yet the procedure was entirely safe and minimal tooth structure was removed.

Figure 11. Physiologic Terminus may actually have different lengths. The walls of the canal on the left are the same, while the walls of the canal on the right have a longer one and a shorter one. Canal length determination is not an exact science; it is an art form. What the rationale of endodontics requires is the entire length of the root canal system be cleaned and shaped. Glidepath is perquisite to this mechanical objective.

Figure 12. Four reasons a file will not “follow” to its terminus: (1) Canal is blocked (2) File curvature does not replicate canal curvature (3) Diameter of file is too wide at its tip (4) Diameter of file is too wide in its shaft. (Often, a combination of reasons one to 4, or all 4 are the situation.)

Third, understand the 4 possible reasons (or a combination of these 4 reasons) why you may not be able to easily follow to the RT (Figure 12).
1. The canal is clogged or seemingly blocked by dense collagen or necrotic debris. This is the fatal flaw of Glidepath preparation. Solution: irrigate thoroughly with sodium hypochlorite, make an abrupt apical curve on smallest file in your armamentarium (typically a size No. 6 or No. 8 file), imagine successfully reaching the RT (actually imagine seeing the file at the RT while examining the pretreatment radiograph or digital image), “follow” gently to and touch the blockage, remove the file, irrigate, re-curve the last millimeter of the file and repeat until the file moves deeper into the canal (Figure 13). Extreme restraint is required here and, at the same time, extreme intention. If you are patient and delicate enough, and if you do not put a time limit on this essential skill, I promise you that you will eventually “follow” successfully to the RT!
2. The angle of access and the angle of incidence are not the same. In other words, the file curvature and the canal curvature do not mimic each other. Solution: The key here is randomization. Rather than think “the canal goes left,” or “the canal is coming toward me,” instead simply allow the file to “follow” to the RT with little or no concern which direction it curves apically. Your only concern or outcome is to reach the RT. So, if you do not reach the RT with the first apical curve that you make, make a different curve and “follow” with that file. Then, if you do not reach the RT, make another different curve, and so on. Maybe multiple apical curves will be the answer. The guideline again is patience, restraint, and gentleness. NEVER FORCE OR PUSH! NEVER, EVER! Forcing is a natural response and must be resisted for Glidepath success. Being aware of the tendency and immediate normal reaction to push when you encounter resistance is the first step to overcoming making the “fatal flaw” worse. Relax; take your time. Once you successfully reach the RT, the rest is easy; simple mechanics. How you manage this moment in Glidepath preparation is the difference that makes the difference.
3. The diameter of the file is too wide for the canal that it is following. In other words, the file does not fit. Solution: Easy. Choose a smaller file. At no time do you know what solution will be the answer. You use all the solutions 1, 2, and 3 all at once. Be delicate. Change the curve. Go to a smaller file. You do not care what the solution is; you only care that you reach the RT.
4. The shaft of the file is too wide for the canal. In other words, the file cannot “follow” deeper into the canal because restrictive coronal dentin will not allow it. Remember, pulps not only inflame and necrose coronal-apically, they also calcify coronal-apically. Solution: Sometimes changing to a smaller file with a narrower coronal diameter will allow the file to “follow” deeper. A second method to remove restrictive dentin is to mechanically remove the restrictive dentin using Gates Glidden drills or nickel titanium rotary files short of the depth followed by the manual file. Historically, this approach has been referred to as early coronal enlargement. Progresssively tapered files (such as ProTaper Universal [DENTSLPY Tulsa Specialties]), used in a brushing motion, are particularly effective and efficient for restrictive dentin removal through the technique. A third method for restrictive dentin removal is the “envelope of motion” manual motion which is described below.
Seemingly, while all 4 Glidepath “following” skills are separate, they are not. Often combinations of the 4 conditions exist, requiring a combination of solutions. For example, a canal might be packed apically with necrotic debris, have restrictive dentin, and you may choose a file that is too wide. Without being delicate, removing restrictive dentin and choosing a narrower file all at the same time is a recipe for failure to follow to the RT, which is the critically essential step of a successful Glidepath.
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.”

Figure 13. “Follow” files are more effective when curved. First squeeze cotton pliers against file shaft at right angles and sweep the cotton pliers toward the tip (left). The resulting file (right) has a gentle and continuous curve to and through its tip.

Figure 14. Glidepath “following” requires optimum tactile sense. Loose gloves do not enable the dentist to feel the file handle (left). Gloves must fit tight so that the balls of the fingers together allow the finest possible touch and delicacy (right).

Figure 15. ProFile Series 29 files (DENTSPLY Tulsa Specialties). These files offer the finest manual transition between Glidepath files because of their constant and appropriate size increases.

Figure 16. New PathFile rotary Glidepath files (DENTSPLY Tulsa Specialties). These robust files, when used properly, can prepare a Glidepath that is safe and precise. While a manual Glidepath is still recommended, the PathFile is an excellent way to increase rotary shaping safety.

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. 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.