Oral Health Group
Feature

How Apical Enlargement Facilitates Irrigation

May 1, 2011
by Justin Kolnick, DDS


INTRODUCTION
Instruments shape and irrigants clean, right? That may sound good as an advertising slogan but we have to dig a bit deeper for the whole truth.

There is a widely held belief that most endodontic failures are caused by inadequate cleaning, debridement and disinfection, especially when it occurs in the apical third of the canal. Baugh and Wallace extensively researched the literature on this topic and concluded that larger apical preparations result in better canal debridement and reduced bacterial count.1 The degree of cleanliness of “smaller” preparations when compared to “larger” preparations is at best, equal, but most studies show it is worse. Yet our tradition is to keep preparations as “small” as possible to: a) avoid iatrogenic errors; b) accommodate certain obturation techniques; and c) save time. In doing so we depend heavily on irrigation (more so than instrumentation) to render canals clean.

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How efficacious are our irrigation and instrumentation techniques when it comes to cleaning canals?

There are many studies that show irrigation cannot often overcome inadequately instrumented canals. Allen showed that when canals were underprepared, irrigation did not render them clean in the apical third – 97% of the time.2 Similarly, Siqueira et al and Hülsmann et al in a series of studies compared various instrumentation techniques and found that none could adequately debride the main canal of the root canal system.3,4 Peters et al compared four NiTi preparation techniques and found that up to 40% of canal surfaces were untouched by mechanical instrumentation, regardless of the technique used.5

While rotary Ni-Ti files have made our instrumentation techniques easier and faster, debris frequently remains in the apical one-third after instrumentation and irrigation. Part of the challenge could be that irrigant may not reach the apical few millimeters. Chow demonstrated that the irrigant does not travel much further apically than the end of the irrigation needle tip.6 In most cases when we perform endodontic treatment, needle penetration is well short of the WL, mostly as a result of under-preparation of the root canal system. While this is helpful in minimizing the risk of an irrigation accident, it prevents effective delivery of the irrigant to the apical third of the canal. In addition, Tay et al confirmed that an apical vapor lock (air bubble) resulting from tissue dissolution by NaOCL prevents irrigant from reaching full WL.7 These two factors greatly inhibit our ability to adequately clean the apical third of the canal by way of irrigation irrespective of how much irrigant is used.

To summarize, there are at least three reasons why we cannot rely on irrigation to adequately clean canals in the apical few millimeters: 1) the needle is too large or we purposefully keep it short to avoid an accident; 2) positive pressure can’t push the irrigant much further then the tip of the needle itself, and; 3) an air pocket can keep the irrigant from reaching WL.

DO LARGER PREPARATION SIZES RESULT IN MORE FFECTIVE IRRGATION? 
The need for adequate enlargement of root canals to improve irrigation efficacy was recognized by Grossman many years ago.8 Falk demonstrated that irrigation was significantly less effective in canals prepared to size #36 compared to those prepared larger.9 Brunson demonstrated that canals instrumented to larger sizes resulted in a statistically significant increase in the volume of irrigant delivered.10 Clearly, when it comes to canal cleaning, a greater volume of irrigant passing through the canal system is more desirable than less irrigant. Of the two choices (small vs. large), it appears that larger preparations facilitate more effective debridement, irrigation and disinfection.

To achieve larger apical preparations, safely, I have found LightSpeedLSX (Discus Dental LLC, Culver City, CA) to be invaluable. In its original form (stainless steel and hand-driven), Canal Master was developed by Drs. E. Steve Senia and William Wildey at the University of Texas Health Science Center at San Antonio in the late 1980s (Figs. 1a&b). In its present form, LightSpeedLSX (NiTi rotary), evolved throughout the 1990s and 2000s from improvements made to earlier versions. LightSpeedLSX has a very short cutting blade, a non-cutting pilot tip and a smooth flexible taperless shaft (Fig. 2a). This affords it maximum flexibility to negotiate curves and cut dentin from canal walls maintaining canal anatomy without the need for excessive mid-root or coronal over-enlargement (Fig. 2b). Tactile feel is unequaled because only the very tip of the instrument comes in contact with canal walls. LightSpeedLSX is extremely safe due to its safety release feature which causes the instrument to separate at the handle instead of at the tip when excessive twisting forces are encountered (Fig. 3).

LightSpeed’s instrumentation concept is simple. Each canal is custom prepared to a size based on its pre-instrumented anatomy. In other words, large canals are prepared large with large instruments and small canals are prepared small with small instruments. The differences that set LightSpeedLSX apart from the rest are: a) its unique design allows for very accurate determination of the canal’s apical diameter (size), called the Working Width (WW); b) its ability to prepare canals to much larger sizes, safely; and, c) the risk of overpreparing the coronal aspect of the canal, ledging, transporting, and breaking are minimized due to its non-cutting tip, short cutting blade and taperless non-cutting extremely flexible shaft.

The concept of Working Width (WW) was first described by Dr. Jou in the April 2004 publication of Contemporary Endodontics: Dental Clinics of North America. A canal’s Working Width is its horizontal width (diameter) just coronal of its apical constriction, roughly 1 to 2mm short of the foramen. Being three-dimensional, canals have both a length (Working Length) and also a width (Working Width). Both are equally important, but for the most part the WW has been ignored because measuring it accurately has been problematic.

Most canals are oval, even in the apical third, and therefore they have both a short and a long diameter (Fig. 4). The concept of preparing canals to the correct WW is new to most dentists. Basically, canal preparation should continue to a size large enough to scrape debris from all canal walls (its circumference) – effectively turning the original oval shaped canal into a round canal (in the cross-section view) (Figs. 5a&b). It is the long diameter that approximates the correct WW. Clinically speaking, the proper WW is achieved when reaching an LSX instrument large enough to fully engage the canal’s circumference, 4mm (or further) short of WL, and a firm push is required for the instrument to reach full WL (Fig. 6). The LightSpeedLSX instrument which accomplishes complete debridement of the apical third is called the Final Apical Size (FAS) (Fig. 7). Typical Working Width sizes reported in the literature are illustrated in Figures 8a&b. Using extracted teeth for practice, this technique is quickly learned and the results can be visualized by simply cross-sectioning roots after instrumentation.

A common criticism of the system is that it uses more instruments than most other systems. We know that canals vary widely in diameter in the apical third. A large canal, size #70, cannot be thoroughly debrided with a #30 size instrument! Other systems simply ignore this fact or suggest the use of hand instrumentation to finish the job. Conversely, the LightSpeedLSX system includes all the instrument sizes needed to address nearly 100% of canal Working Widths and thus it appears that more instruments are needed. I have found that it takes very little time to prepare canal correctly (to Working Width) with LightSpeedLSX compared to leaving canals under prepared in the apical third when using other tapered NiTi rotary systems. Besides, it is impossible to ad
equately prepare the true WW of a curved canal with a large tapered rotary NiTi file without significantly altering canal anatomy.

IS APICAL NEGATIVE PRESSURE IRRIGATION A GAME CHANGER?
Conventional irrigation has shown to be only moderately effective, at best, when it comes to cleaning canals, particularly in the apical few millimeters. However the game has changed with a new device called EndoVac (Discus Dental LLC). Dr. John Schoeffel, inventor of EndoVac, literally revolutionized the world of intracanal irrigation (Fig. 9). While most all other systems utilize positive pressure to force irrigant into the canal and/or dynamic motion to agitate the irrigant, EndoVac uses negative apical pressure (suction). Simply put, EndoVac creates an area of low pressure (vacuum) at the very end of the root canal. This causes the irrigant, placed in the chamber by the Master Delivery Tip (MDT) (Figs. 10a&b), to be swiftly drawn from the chamber, down the walls of the canal taking with it floating debris which enters into the end of either a large (Macro) or small (Micro) cannula. Once captured by the cannula the irrigant and debris are evacuated from the canal through the Multi Port Adapter (MPA) (Fig. 11) which is connected to the chairside Hi-Vac system. The irrigant flow rate through the canal is said to be as rapid as the speed of water passing over the Niagara Falls (Fig. 12).

EndoVac utilizes two cannulas for evacuation. The Macro­Cannula (Fig. 13) is used first for the removal of large debris from the mid-root and coronal sections of the canal. Then, the MicroCannula (Figs. 14a&b) is used similarly but at full WL. The MacroCannula tip size is 0.55mm whereas the MicroCannula has a diameter of size 0.32mm. Therefore, the canal must be prepared to at least a size #35 to ensure the MicroCannula tip will reach full WL. Fortunately, preparing to size #35, and much larger, is easy, fast and safe when using LightSpeedLSX.

The EndoVac protocol consists of first clearing the canal of any large debris by depositing NaOCL (6%) in the chamber with the MDT while creating a suction with the MacroCannula placed at approximately mid-root (Fig. 15). Then, replacing the Macro with the MicroCannula, a series of 3 micro cycles are completed with the tip of the MicroCannula at full WL. The first micro cycle suctions NaOCL through the canal for 30 seconds for the purpose of dissolving any remaining tissue in the apical canal. The second micro cycle suctions EDTA, for 30 seconds, through the canal to remove the smear layer. Finally, the third micro cycle again suctions NaOCL through the canal for 30 seconds to aid in penetration of NaOCL into the now open dentinal tubules. Between each cycle, the irrigant is allowed to soak for 60 seconds in the canal before progressing to the next step.

Research shows that significantly better debridement occurs at 1mm from WL (366% cleaner) when using EndoVac compared to positive pressure needle irrigation.11 EndoVac also delivers irrigant to the apical 3mm without any risk of extrusion beyond the foramen which can lead to severe pain, facial swelling and both temporary and permanent paralysis (Fig. 16).12,13 Since EndoVac creates suction at the very end of the canal it is able to remove the vapor lock (air bubble) from the canal terminus thus allowing irrigant to reach the very end of the canal.

EndoVac solves all three problems noted earlier which can limit our ability to effectively irrigate the apical third (physical limitations, irrigant flow restrictions and air pockets). It is simply a better way of irrigating the canal when compared to conventional needle and agitation type irrigation methods. I have found it well worth the extra few minutes EndoVac takes to irrigate the canal system really well. I’m still amazed at just how much debris is suctioned from the canal through EndoVac’s clear tubing even after I believe the canal is completely “clean”.

COMBINING OPTIMAL IRRIGATION AND EFFECTIVE  INSTRUMENTATION
There are many places in the canal system for bacteria to hide from our instruments and irrigation technique. However, this reality should not dissuade us from doing the very best we can to mechanically debride and irrigate the canal, particularly the apical canal. While it is true that we must rely on irrigation and disinfection to do its part, the question then becomes, “just how much should one rely on mechanical debridement versus chemical irrigation/disinfection?” Clearly, both our current instrumentation and conventional irrigation techniques afford some room for improvement when it comes to consistently rendering clean canals.

No matter which system(s) you choose, no instrument and irrigation technique can achieve complete debridement of the entire root canal system every time. However, you can improve your odds by selectively choosing the best instrumentation and best irrigation systems for cleaning the apical third of the canal. I have found the combination of LightSpeedLSX and EndoVac to be the most effective combination for the removal of debris and bacteria in the canal. When EndoVac was used in combination with LightSpeedLSX, Vasundhara and Prashant showed that canals were 99% and 99.5% free of debris at the 1mm and 3mm level respectively.14

In our office, final disinfection of the canal (after debriding with LightSpeedLSX and irrigating with EndoVac) is achieved with an Er, Cr:YSGG laser with radial-firing tips – but that’s a topic for another article!

CASE STUDY
Figure 17 is the pre-treatment radiograph of a case (tooth #18) diagnosed with chronic apical periodontitis. After access, hand files were used to create a reproducible glide path to WL followed by crown-down flaring to remove the coronal canal curvature (restrictive dentin). Apical instrumentation was initiated with the size #20 LightSpeedLSX and followed with sequentially larger LSX sizes until the apical third was fully prepared to the proper Working Width. Enlarging the canal further would have needlessly removed sound dentin and weakened the tooth. The Final Apical Sizes were #55 in each mesial canal and #70 in the distal canal.

The canals were filled with Resilon® (Sybron Endo, Orange, CA) using the continuous wave technique with HotTip (Discus Dental LLC) (Fig. 18) and backfilled with warm Resilon delivered by the HotShot (Discus Dental LLC) gun (Fig. 19). Figures 20 and 21 show the post-treatment and twelve month follow-up radiograph.

CONCLUSION
Effective debridement, irrigation and disinfection of the root canal space are critical to the success of endodontic treatment. A protocol using LightSpeedLSX instrumentation and EndoVac has been presented to show how this can be accomplished safely. Utilizing this protocol improves removal of bacteria and debris by: enlarging the canal to the proper WW for better debridement, ensuring that irrigant reaches the very end of the canal without risking apical extrusion; ensuring debris is evacuated completely from the canal, and finally, facilitating canal enlargement so that disinfection with laser energy is possible to full working length.

In the current dental climate with the high retention rate of dental implants, I have found that dentists have become less confident in their ability to predict endodontic outcomes. They are therefore more reluctant to recommend endodontic treatment (retreatments in particular) to their patients. Let’s strive to raise the bar in endodontics to the next level, giving both dentists and patients a safe and effective choice when deciding upon alternative treatment plans.OH

Dr. Kolnick is in private practice, limited to endodontics, in White Plains and Mt. Kisco, NY. In 2008, Advanced Endodontics of Westchester became one of the first laser-assisted microendodontic practices in the country and recently incorporated CBCT into both of its offices. Dr. Kolnick was as an Associate Clinical Professor in Endodontics at Columbia University, a
n Attending at Westchester Medical Center and an Associate Clinical Professor in Endodontics at New York Medical College. Dr. Kolnick received a small honorarium from Discus Dental for writing this article. Email: info@westchesterendo.com

Oral health welcomes this original article.

REFERENCES
1. Baugh D, Wallace J. The role of apical instrumentation in root canal treatment: a review of the literature. J Endod 2005;31:333-340.
2. Allen F. In vivo study of apical cleaning. General Dentistry 2007;449-456.
3. Siqueira et al. Histological evaluation of the effectiveness of five instrumentation techniques for cleaning the apical third of root canals. J Endod 1997;23;8;499-502.
4. Versumer, Hulsman, Schafers. A comparative study of root canal preparation using Profile and LightSpeed rotary Ni-Ti instruments. Int Endod J 2002; 35, 37-46.
5. Peters OA, Schonenberger K, Laib A. Effects of four Ni-Ti preparation techniques on root canal geometery. Int Endod J 2001;34(3):221-230.
6. Chow, TW. Mechanical effectiveness of root canal irrigation. J Endod 1983; 9;475-479.
7. Tay F, et al. The effect of vapor lock on root canal debridement using a side-vented needle for positive pressure irrigant delivery. J Endod 2010;36;745-750.
8. Grossman L. Irrigation of root canals. J Am Dent Assoc 1943; 30;1915-1917.
9. Falk et al. The influence of preparation size on the mechanical efficacy of root canal irrigation in vitro. J Endod 2005; 31;742-745.
10. Brunson, et al. Effect of apical preparation size and taper on irrigant volume delivered by using negative pressure irrigation system. J Endod 2010, Apr; 36; 4;721-724.
11. Neilsen BA, Baumgartner JC. Comparison of the EndoVac system to needle irrigation of root canals. J Endod 2007, 33:5:611-615.
12. Desai, Himel V. Comparative Safety of Various Intracanal Irrigation Systems. J Endod, April 2009, Vol. 35:4: 545 – 549.
13. Mehdipour, Kleier, Averbach. Anatomy of Sodium Hypochlorite Accidents. Clinical Techniques in Endodontics. Compendium, October 2007.
14. Vasundhara S., Prashanth B. R. Efficacy of EndoVac irrigation System for apical debris removal compared to conventional in root canals prepared with LSX- An in vitro study. Dept. of Conservative Dentistry & Endodontics, College of Dental Sciences, Davangere. 2008 Submitted for publication.