Manual Versus Mechanical Endodontic Glidepath

GLIDEPATH BACKGROUND KNOWLEDGE
In order to answer the question of “manual versus mechanical endodontic Glidepath,” the following observations about root canal system anatomy need to be understood by the dentist:
Observation 1. Most root canal system foramina (or portals of exit [POEs]) are at least the minimal diameter of a No. 15 or more manual endodontic file. Test this yourself by taking extracted teeth and slide a No. 15 file into the apical region POEs. Typically, the file will easily follow up the apical end of the root canal system one to 2 mm. If the file slides 2 mm into the canal, it means the minimal apical POE diameter is larger than a No. 15 file, given the No. 15 file has a 2% taper. This also means that if a No. 10 file is deftly followed through the PT to the RT or slightly beyond in order to preserve POE patency, no damage will occur to the fragile POE anatomy. All of nature’s canals are curved to varying degrees (Figures 1a to 1f).
Observation 2. All root canal systems are different from all other root canal systems. Each and every one of them is individually unique and novel. Each one you encounter is a perfect stranger!
Observation 3. Perhaps as many as 50% of canals are already essentially smooth-walled tunnels, albeit some or parts of them are much narrower than a No. 10 file.
Observation 4. Canals calcify from crown toward apex. After pulpal trauma (impact, caries, caries removal, caries repair, or aesthetic restorative preparation), nature may respond by the dental pulp either becoming necrotic and/or calcific. Nature never finishes the obturation, however! She only starts it. The dentist’s job is to find the entrance of the canal without perforating or unnecessarily removing precious tooth structure. Once the canal entrance is discovered, the Glidepath is made using disciplined endodontic mechanics (Figures 2a to 2n).
GLIDEPATH GUIDELINE CONTROVERSIES
There are 2 Glidepath controversies brewing in endodontics. First, is the Glidepath even necessary? Of course if the Glidepath already exists for a given canal, then creating one is not necessary. The second controversy is, can the dentist immediately start with either full rotary or reciprocation? Reciprocation movement is the mechanical expression of the balanced force motion. The real question is, do you need manual confirmation of the existence of, and if not, the creation of a Glidepath before considering a mechanical Glidepath? How do you find out? In order to answer the Glidepath controversies, 2 questions and their answers, is the subject of this article:

Question No. 1: To Have a Glidepath or Not to Have a Glidepath? “How Do I Choose?”
What to do before a “super loose” No. 10 file? How do you get there? What endodontic mechanics do you need to perform? The key distinction is the notion and skill of “following” (Figures 2a to 2n). Once obvious restrictive dentin is removed either manually or with rotary, it is necessary at some point that the dentist decide that now is the time to follow to the RT. In other words, the clinician certainly can benefit from a “crown-down” preparation approach or “pre-enlargement” or “pre-flaring” or “early coronal enlargement.” All these terms refer to the same goal of removing restrictive dentin whenever present. However, whether pre-enlargement is your preferred protocol or whether you assume you already have enough room to follow to the RT, there is an intentional moment in time to follow a small file to the RT. In the past, this step has been referred to as “length of tooth.” If a No. 10 file easily follows in the coronal one third, I usually make the decision to now follow to the RT, especially if the file follows easily. Think of this as simply “riding” the file to the RT just like a child rides down a slide in the park. No steering; just randomly “going with the flow” of the slide. Since the length of tooth is dynamic and rapidly changes during rotary design, I prefer to simply refer to the “first instrument to the RT.” And the “instrument to the RT and eventually to the PT” will change. Its length will become shorter and should be verified toward the end of shaping using radiographic images to be sure but primarily using the determination and validation of an accurate apex locator reading. The actual last rotary instrument used can be used for the apex locator reference instrument. When the last rotary file resists apical manual progress and the apex locator indicates the PT, then the clinician is now able to measure both the length and minimal apical diameter of the root canal preparation. These measurements are discovered at the end of cleaning and shaping and cannot be determined with the first instrument to the PT since all the measurements will change during radicular shaping.

The following are 3 example simulations that will be used to describe the following to the RT skill:
Example 1. Irrigate thoroughly with sodium hypochlorite. Precurve No. 10 file using metal cotton pliers. Follow gently yet intentionally No. 10 file to RT (Figure 2d). Begin smoothing manual motion. Make small, one-mm amplitude coronal and then apical vertical strokes (Figures 2g to 2k). Maintain apical extent of stoke at PT or slightly beyond RT. Do not allow amplitude to increase inside the PT until the file easily moves in and out from slightly past RT to slightly short of PT. Then increase vertical stroke amplitude once smooth Glidepath evolves. Increase vertical amplitude strokes until you can withdraw and follow to RT easily and effortlessly. The Glidepath is complete when the No. 10 file is “super loose.” Begin rotary. If a bigger tunnel is desired, proceed with No. 15 using balance manual motion or series 29 hand files sizes No. 1 to 3 (DENTSPLY Tulsa Dental Specialties) or PathFile sizes No. 13, 16, and 19 (DENTSPLY Tulsa Dental Specialties).
Example 2. Irrigate thoroughly with sodium hypochlorite. Precurve No. 10 file using metal cotton pliers. Follow gently yet intentionally No. 10 file to RT. If No. 10 file does not easily follow to RT, do not follow deeper because you may inadvertently start a dentin mud block or begin an undesirable ledge. What is next? Envelope to the right on a withdrawing stroke, follow deeper and repeat until RT is reached.3 This may take several envelopes, and then follow manual, motions. Once RT is reached begin smooth motion, or “smoothies” as I prefer to call them, until “super loose” No. 10 file with first short vertical strokes and then longer ones until you “own the Glidepath.” Now you are ready for rotary.
Example 3. Same as No. 2, but No. 10 file does not follow to RT after envelope motions. Withdraw file, recurve and repeat No. 1 and repeat again until the RT is reached. Then proceed with “smoothies,” finish Glidepath, and begin rotary.

Question No. 2: Manual Versus Mechanical Glidepath: “How Do I Choose?”
What to do after a super loose No. 10 file? The second debate, or better described as a current trend, is whether to prepare a wider Glidepath manually or mechanically. Again, I define the successful Glidepath as “smooth walls that are created with and measured by a super loose fitting No. 10 endodontic file.” Glidepath validation occurs when the No. 10 endodontic file can be easily used in an in-and-out smoothing motion of increasing amplitudes: first short in and out one mm amplitude smoothing strokes, then several millimeters, and then finally the capacity to slide from midway down the canal to the RT in broad multiple millimeter amplitudes. The No. 10 file can safely and easily pass past the PT since most apical foramina are larger than the diameter of a No. 15 file (Figures 3a to 3d). The purpose of the No. 10 file is to confirm PT patency and then shape with rotary short of the PT. If the No. 10 file is deftly and delicately followed to the RT or a millimeter beyond, no significant change in the delicate foraminal anatomy occurs. At this point, clinicians can usually proceed with rotary using their favorite successful rotary technique. Some colleagues, however, prefer a larger diameter Glidepath in order to increase safety. After all, narrow canals present a greater risk of breakage. It is at this point that many dentists proceed with a No. 15 endodontic file. To me, this is potentially the most dangerous manual file in the world. The reason is that the file tip (DO) is 50% wider in diameter than a No. 10 file. Therefore, the No. 15 file does not easily follow the Glidepath prepared with a No. 10 file. Experience suggests ledges and blocks and even canal transportation occur most often in endodontics with the use of the No. 15 file. There is, however, a safe method to increase Glidepath size by using the “balance” technique.4 This method is extremely efficient and safe. Some dentists, in addition, have been trained that the ideal Glidepath diameter should be a No. 20 file. The problem with the No. 20 endodontic file is that it is the second most potentially dangerous manual file in the endodontic armamentarium. The reason is that the No. 20 file is one third wider at (DO) than the No. 15 file! Once again, there is a significant possibility that the No. 20 file will not easily follow the No. 15 Glidepath and blocking, ledging, and therefore there is continued risk of transporting the canal internally and/or externally. Given that the balance manual motion is used, however, the Glidepath diameter can usually be increased to No. 15 or No. 20 safely and predictably.5,6
Another method to increase Glidepath diameter is to use narrow rotary files such as the newly introduced PathFile (Figures 4a to 4d). These relatively robust instruments, while designed for rotary, can be used manually if the dentist is fearful of breakage (Figures 5a to 5e). However, many endodontists and general dentists are enjoying safe and successful use of the PathFiles.7 These files should not be used for shaping, as the shape is essentially parallel and not funnel-shaped. The finished preparations would be insufficient to evoke the required apical and lateral 3-dimensional (3-D) hydraulics’ successful obturation. It is the continuously tapered funnel preparation that provides the needed space for 3-D cleaning, successful conefit, and 3-D packing of the entire root canal system.