Written by John West, DDS, MSD Thursday, 06 January 2011 14:11
In the September 2010 issue of Dentistry Today, the first of 3 articles on the endodontic Glidepath entitled The Endodontic Glidepath: "Secret to Rotary Safety" (available for review at dentistrytoday.com) focused on what, how, when, and why endodontic rotary safety is dependent on the clinical skill of endodontic Glidepath preparation.1 The author explored the critical clinical elements of what, why, and how to make a Glidepath.2 The next important endodontic Glidepath questions facing dentists today are when and how should you begin mechanical radicular preparation? How do you choose, when do you choose, and if you choose, how and when do you choose? When is the endodontic Glidepath ready for safe rotary?
In the previous article, the endodontic Glidepath was defined as a "smooth tunnel from the chamber orifice of a canal through its physiologic terminus (PT)." It was suggested that the only way to ensure smooth patency from orifice to PT was to use the radiographic terminus (RT) as the default of home base guideline landmark destination unless clear evidence exists that the PT and RT are more than a millimeter different. If there is a PT/RT difference greater than one millimeter, then discard the RT length and consider the Glidepath length to be one millimeter past PT, as identified with an accurate apex locator reading. While the diameter of an appropriate Glidepath is argued in the literature from sizes ranging from a "super loose" No. 10 endodontic file to a size No. 20 file or bigger, most masterful endodontic clinicians agree that the Glidepath walls should be smooth and biomimetic for rotary success and safety.
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).
|Figures 1a to 1f. Root Canal System Anatomy. (a to e) Note single canals have multiple and different canal curvatures. (f) Each canal in scanned human molar demonstrates that canals do not present as straight, but rather they resemble "banners in the breeze." Appreciation and awareness of the uniqueness of every endodontic canal is the first step toward preparing successful rotary Glidepaths. Source: eHuman.com, a Brown and Herbranson Company.|
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.
|Figures 2a to 2n. Manual Glidepath. (a) Pretreatment of maxillary premolar with tortuous root canal system anatomy and requiring a Glidepath confirmation. (b) Curved file "following" canal toward its radiographic terminus (RT). (c) Apical progress of file slows due to apparent curvature. (d) Envelope out and make different curve on file with metal cotton pliers. (e) Follow deeper as canal permits. (f) File easily follows to physiologic terminus (PT). (g) Follow file to RT. Begin small amplitude vertical strokes at the RT or one mm longer. (h to m) Increase vertical amplitude of "smoothing" motion until you "own the Glidepath." You have complete confidence that you have smooth walls and that the super loose No. 10 file rides up and down the Glidepath walls without restriction. The No. 10 file is completely free. (n) Glidepath is ready for safe rotary. (Note: The author is grateful to Dr. Clifford J. Ruddle for supplying the exceptional graphic animations for Figures 2b to 2n. Please refer to endoruddle.com for exceptional educational resources including computer animation of the still images in this article.)|
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.1
|Figures 3a to 3d. Manual Files and Portals of Exit Diameters. (a) The first 3 manual files of most dentists' armamentarium (the Nos. 10, 15, and 20) have poorly sized progressive tip diameters in terms of successfully preparing a smooth radicular Glidepath for safe rotary. (b) No. 20 files easily inserted in extracted mandibular molar apical foramina. (c) Closeup of Figure 3b. (d) No. 25 files easily inserted into foramina of another extracted mandibular molar, demonstrating further that a No. 10 file could safely pass the foraminal constriction when confirming patency during Glidepath preparation.|
In today's technology the only sure way to determine a Glidepath is if you can "slip and slide" easily from the orifice to the RT with an endodontic file. Some teachers/advocates may suggest to the dentist that no Glidepath is necessary, so begin Glidepath preparation with a rotary instrument. The problem is, they might be right, but they might be wrong. Test this yourself. Take 10 extracted teeth, prepare a proper straight-line access and take your favorite rotary file system and see if you can follow the canals to their POEs without first determining if you can follow to the RT with a manual file. Depending on the age of the teeth at the time of extraction, there may be a wide range of results. If all the teeth are removed for orthodontic reasons, then most of the canals will be large, and a rotary instrument can safely follow to their POEs most of the time. The watchword here is "most of the time." As always, unless a Glidepath exists or is made, rotary and/or reciprocal mechanical endodontics is dangerous. If the teeth you select are adult teeth and particularly if heavily restored, your favorite rotary system may not even fit in the orifices! My experimental testing experience is that I can follow to the terminus of root canal systems 25% to 75% of the time using a ProTaper Shaper 1 (S1) (DENTSPLY Tulsa Dental Specialties) or smallest PathFile (DENTSPLY Tulsa Dental Specialties). The big problem is that the dentist does not know, nor does anyone else, which canals can be initially followed with rotary and which cannot. This is extremely dangerous. If a natural Glidepath is not present, mechanical files will eventually break, block, and shelf. The Glidepath can be lost and impossible to regain. To me, these are very bad odds. "Assuming" or hoping a Glidepath is present is the wrong thing to do. It does not matter who is teaching this. But if you've read this article this far, then you are ready to find out for yourself and run the 10 teeth experiment I have suggested. As you have honestly done the experiment, you will either discover you already have a Glidepath or you will discover you do not have a natural Glidepath. If not, the next step is to carefully prepare one and then begin cleaning and shaping. In summary, the take home message here is: "No confirmed Glidepath, then no rotary." Period.
|Figures 4a to 4d. Mechanical Glidepath. (a) New PathFiles (DENTSPLY Tulsa Dental Specialties). (b) Closeup of tip of PathFile. (c) Square cross section of PathFile gives it good strength. |
(d) Cutting blades.
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.
This article, the second in a series of 3 articles on the endodontic Glidepath beginning with the September 2010 issue of Dentistry Today (archived articles can be found at dentistrytoday.com), represents an inquiry into the critical distinctions of the endodontic Glidepath. First, we reviewed the need for a confirmed and reproducible Glidepath as prerequisite to rotary or reciprocal shaping. In order to be safe, before rotary shaping, the dentist must always discover that a Glidepath already exists or that one needs to be created.
Second, an emphasis was placed on a "finishing checklist" for Glidepath preparation for safe and successful rotary. The checklist is 2 parts: (1) minimum super loose No. 10 file sized k tunnel is verified; (2) the super loose No. 10 file sized tunnel must run from canal orifice through the canal PT to the RT. In this way, patency is preserved and yet the delicate and often fragile cemental anatomy remains undamaged and unchanged, therefore meeting Schilder's8 fourth mechanical objective of "keeping the foramen as small as practical."
Third, we discussed that the question should not be "manual versus mechanical" but rather "manual, then mechanical." Always measure the existence of a Glidepath with manual before mechanical.
The key elements for improving your performance of Glidepath mastery include a clear intention of what needs to be accomplished and yet at the same time, restraint; gentleness; copious irrigation with sodium hypochlorite; curved files; randomness; discovery; expecting the unexpected and surrendering to, honoring, and respecting the delicate anatomical structure called the root canal system. After all, nature has been demonstrating how to make a Glidepath for a long time, but we have not been paying attention. We have been too heavy-handed, we have pushed, we have forced, and we have not always been good stewards of nature's fragile framework. She has been giving us and teaching us the Glidepath answer all along. Listen to Mother Nature as she sends her legacy to us: "You have never seen a canal like me before. I am full of curves and booby traps. Treat me gracefully—I know that may sound corny—and respect my delicate tissues and structures. I am waiting for you. All you have to do is follow me to my end. Make me smooth and big enough for safe rotary and you can have your way with me. Once cleaned, shaped, and packed, I will reward you with the gift of healing."
In an upcoming issue of Dentistry Today, I will present useful guidelines for implementation of the endodontic Glidepath. Remember, knowing what to do is only half the answer to mastering elegant, artistic, and successful Glidepaths. The other half is to be able to bring these skills into the everyday clinical practice; implementation is often the missing link. In order to do this, you will need a plan to design a culture, environment, and ergonomics in your office that will allow the time and energy to do it right.
- West JD. Endodontic Glidepath: "Secret to Rotary Safety." Dent Today. 2010;29:86-93.
- West J. The Magic of Mastering the Glidepath: What Every Endodontist Should Know. Paper presented at the American Association of Endodontists Annual Session; April 16, 2010; San Diego, Calif.
- Machtou P, Ruddle CJ. Advancements in the design of endodontic instruments for root canal preparation. Alpha Omegan. 2004;97:8-15.
- West J, Roane J. Cleaning and shaping the root canal system. In: Cohen S, Burns RC. Pathways of the Pulp. 7th ed. St. Louis, MO: Mosby Year-Book; 1998:203-257.
- West J. Endodontic predictability–"Restore or remove: how do I choose?" In: Cohen M, ed. Interdisciplinary Treatment Planning: Principles, Design, Implementation. Chicago, IL: Quintessence Publishing Co: 2008:123-164.
- West J. Endodontic Update 2006. J Eshtet Restor Dent. 2006;18:280-300.
- Berutti E, Cantatore G, Castellucci A. Use of nickel-titanium rotary PathFile to create the glide path: comparison with manual preflaring in simulated root canals. J Endod. 2009;35:408-412.
- Schilder H. Cleaning and shaping the root canal. Dent Clin North Am. 1974;18:269-296.
Disclosure: Dr. West is co-inventor of ProTaper and Calamus Technologies.
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