Shaping Complex Canals - dentalCEtoday.com · size of the access cavity is dictated by the position of the oriﬁces on the pulpal ﬂoor. The axial walls are extended laterally such

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Continuing Education

Shaping Complex Canals: Clinical Strategy and Technique

Authored by Clifford J. Ruddle, DDS

Upon successful completion of this CE activity 2 CE credit hours will be awarded

Volume 33 No. 11 Page 88

ABOUT THE AUTHORDr. Ruddle is founder and director ofAdvanced Endodontics, an internationaleducational source, in Santa Barbara,Calif. He is an assistant professor ofgraduate endodontics at Loma LindaUniversity and University of California, Los

Angeles, is an associate clinical professor at University ofCalifornia, San Francisco, and is an adjunct assistant professorof endodontics at University of the Pacific, School of Dentistry.As an inventor, he has designed and developed severalinstruments and devices that are widely used internationally.He is well known for providing superb endodontic educationthrough his lectures, clinical articles, training manuals, videos,and DVDs. Additionally, he maintains a private practice inSanta Barbara. He can be reached at (800) 753-3636 or viathe Web site endoruddle.com.

Disclosure: Dr. Ruddle has a financial interest in productson which he collaborates, which includes ProGlider and theProTaper System (DENTSPLY Tulsa Dental Specialties).

INTRODUCTIONMany times throughout several decades, I have describedvarious concepts, strategies, and techniques for shapingroot canals. Although the concepts and strategies haveessentially remained the same, the techniques haveevolved based on the technology available in any given era.As an endodontic educator, I am continuously reminded ofthe criteria dentists deem most important when selecting abrand line of files for preparing canals: namely, a file orshort sequence of files that will optimize safety, efficiency,and simplicity at an affordable price.

As important as the actual mechanical attributes of anygiven brand line is to fully understand the final shape a file,or series of files, can produce. It is imperative to appreciatethat well-shaped canals promote 3-D cleaning and filling

root canal systems (Figure 1).1 This article will focus on theconcepts, strategies, and techniques that may be utilized toprepare longer, narrower, and more curved canals. Themethod I will describe for preparing canals will fulfill thecriteria mentioned above and is proven, easy-to-learn, andreadily transferable.

Concepts for Coronal and Radicular Access The concept of coronal access is to remove the entire pulpalroof, including all unsupported dentin. In furcated teeth, thesize of the access cavity is dictated by the position of theorifices on the pulpal floor. The axial walls are extendedlaterally such that the orifice(s) is (are) just within this outlineform. Coronal access objectives should focus on flaring andflattening the internal axial walls, yet recognize that access tothe underlying root canal system is oftentimes limited. Infurcated teeth, leaving a residual shelf of dentin overlying anyaspect of the pulpal floor compromises identifying hiddenorifices and negotiating canals.

The concept of radicular access is to pre-enlarge the bodyof a canal, which will serve to provide excellent access to thetypically more anatomically difficult apical one-third of thesame canal (Figure 2).2 Radicular access frequently requireseliminating internal triangles of dentin. Further, in multirootedteeth, radicular access should focus on intentionally relocatingthe coronal-most aspect of a canal away from furcal danger.As will be discussed later, radicular access is an extension ofcoronal access and may be immediately performed wheneverthere is sufficient working width to passively accommodatethe tip of a mechanical shaping file.

Strategies for Glide Path ManagementFollowing coronal and radicular access, 2 possibilities existwhen initiating glide path management (GPM) procedures.In roots that hold shorter, wider, and straighter canals, agentle reciprocating handle motion, followed by a fewengaging and outward cutting cycles, will typically pull asize 10 hand file through the canal and to length. When theapical one-third of a canal is negotiated, then workinglength is established, patency is confirmed, and a smooth,reproducible glide path is verified. When necessary, theterminus of any canal should be expanded to 0.15 mm toconfirm sufficient space is available to safely initiate


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Shaping Complex Canals: Clinical Strategy and TechniqueEffective Date: 11/1/2014 Expiration Date: 11/1/2017

mechanical shaping procedures.3

The second clinical possibility that exists whenperforming GPM procedures is encountered in roots thathold longer, narrower, and more curved canals. In morecoronally calcified canals, the inward movement of the size10 file is oftentimes limited because the rate of taper of thisfile initially exceeds the rate of taper of the canal. Ratherthan using smaller size stainless steel (SS) hand files toreach length, a strategy may be utilized that focuses first onpre-enlarging the coronal two-thirds of a canal beforeattempting to negotiate the typically more open apical one-third of the same canal. The secret to pre-enlargement is touse a sequential glide path strategy.

Sequential Glide Path for Shaping CanalsPre-enlargement procedures use a sequential glide pathstrategy in which the clinician scouts, secures, and shapesthe coronal two-thirds of longer, narrower, and more curvedcanals, prior to scouting, securing, and shaping the apicalone-third of the same canal. The concept of pre-enlargementis the antithesis of the so-called crown-down technique.Whereas either method serves to initially open the body of acanal, pre-enlargement safely progresses from small-to-largesize files, whereas crown-down plows away dentin byprogressing from large-to-small size files.

Armamentarium for Preparing CanalsIn the article published in the July 2014 issue of DentistryToday, entitled “Endodontic Canal Preparation: Inno vations

in Glide Path Manage ment and Shaping Canals,” adescription was made of the features, benefits, and clinicaladvantages of Pro Glider and ProTaper Gold (PTG) rotaryfiles (DENTSPLY Tulsa Dental Specialties [DTDS] andDENTSPLY Maillefer) for preparing canals.4 Let’s brieflyreview this armamentarium for preparing canals.

ProGlider is a new dedicated rotary glide path filedesigned to replace a traditional, considerably stiffer, andmore dangerous SS size 15 hand file (Figure 3). ProGliderutilizes M-Wire technology, which has been shown toimprove the resistance to cyclic fatigue by a staggering400%.5 ProGlider has a D0 diameter of 0.16 mm and a D16diameter of 0.82 mm. Strategically, this file has 12 increasingpercentage tapers from 2% to 8% over the length of itsactive portion. One ProGlider can cut a considerably widercanal pathway than any other market version dedicatedglide path multifile sequence.4 Mechanical glide pathprocedures have been shown to improve safety andefficiency, while reducing chair time by up to 40%.6

ProTaper (DTDS and DENTSPLY Maillefer) came tomarket in 2001 and was the first system to offer activecutting edges, a progressively tapered design on a singlefile, and both Shaping and Finishing files.7 During the past13 years, these design features have catapulted thissystem to become the No. 1 selling file in the world, the No.1 file choice of endo dontists, and the No. 1 system taught ininternational dental schools to undergraduate students.4

ProTaper’s dominant success is primarily linked toreproducible final shapes that promote 3-D disinfection and


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Figure 1. This image demonstrates straight-lineaccess; abrupt apical curvature and recurvatureof the P and DB systems, respectively; and atreated furcal canal.

Figure 2. This graphic illustrates endodontic anatomy and a strategy for pre-enlarging the coronal two-thirds before shaping the apical one-third of the same canal.

Figure 3. ProGlider (DENTSPLY Tulsa DentalSpecialties [DTDS] and DENTSPLY Maillefer)has a progressively tapered design and utilizesM-Wire technology. These features make glidepath management safer, faster, and easier.

filling root canal systems. PTG has the exactgeometries as ProTaper Universal (PTU), butfortuitously has been metallurgically enhancedthrough heat treatment technology (Figure 4a).

The PTG Shaping and Finishing files set a newstandard in safety and canal centering bysignificantly im proving flexibility and the resistance tocyclic fatigue, when comparing PTG against PTU orany other brand line of files of like sizes. Like PTU,the PTG Shaping files dominantly prepare the coronaltwo-thirds of a canal, whereas the Finishing files serveto increase the terminal diameter and apical one-thirdtaper of a canal without needlessly further enlargingthe body of the same canal (Figure 4b). BothProGlider and PTG Shaping and Finishing files havebeen validated at 300 rpm and a torque of 4.0 to 5.2Ncm. The following will describe a technique toendodontically prepare longer, narrower, and morecurved canals.

Scout and Secure the Coronal Two-ThirdsIn coronally restrictive canals, after locating any givenorifice, the pulp chamber may be filled brimful with aviscous chelator. It is virtually always possible to inserta size 10 file into the coronal aspect of most canals. Gentlyreciprocating the handle of a size 10 file will generally pull thisfile into the canal several millimeters (Figure 5). In longer andnarrower canals, the size 10 file will generally not reach lengthbecause the rate of taper of this file exceeds the rate of taperof the canal. In these instances, any portion of the overalllength of a canal that can be readily negotiated can typically besecured. The secret to securing canals is to gently work thesize 10 file, utilizing 0.5 to 1.0 mm ultrashort vertical strokes,until it is super loose.8

The loose depth of the size 10 file is measured, and thislength is transferred to either an SS size 15 hand file or,preferably, a safer, faster, and easier to use dedicatedmechanical glide path file, such as ProGlider. The viscouschelator is flushed out and the pulp chamber is filled withsodium hypochlorite (NaOCl). ProGlider’s variably tapereddesign enables this file to passively run inward andprogressively advance along the secured portion of a canal.If the file ceases to easily advance inward, remove the file

and irrigate, recapitulate with the size 10 file, then re-irrigate to liberate this debris. Typically, in one or 2 passes,the ProGlider will rapidly expand or pre-shape the securedportion of any given canal (Figure 6).

Shape the Coronal Two-ThirdsThe coronal two-thirds of virtually any canal can bemechanically shaped when sufficient working width isavailable to passively accommodate the tip of the PTGAuxiliary Shaping file, termed SX. This file has an overalllength of 19 mm, which facilitates its use when space isrestrictive. Further, because SX has 9 increasing tapers upto 19%, it is the industry leader for pre-enlarging the coronaltwo-thirds of virtually any canal (Figure 7). SX is designedso its apical extent passively follows the glide path while thebody of this file is utilized to cut dentin.

Specifically, SX is designed to cut between D6, D7,D8, and D9, where the cross-sectional dimensions areequivalent to 0.5 mm, 0.7 mm, 0.9 mm, and 1.1 mm,


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Figure 4a. ProTaper Gold (PTG) rotaryfiles (DTDS and DENTSPLY Maillefer)increase flexibility and provide more thantwice the resistance to cyclic fatiguecompared to ProTaper Universal (InternalDENTSPLY testing, data on file).

Figure 4b. The PTG Shapers advantageously prepare the coronal two-thirds of a canal; whereas thePTG Finishers prepare the apicalone-third of the same canal.

Figure 5. In the presence of a viscouschelating agent, a size 10 file may be utilized to scout and secure a glide pathover any length of a canal.

Figure 6. In the presence of sodiumhypochlorite (NaOCl), ProGlider may beused to safely and rapidly pre-shapethe secured portion of a canal.

a b

respectively. In the presence of NaOCl, SX is usedlike a brush to laterally and selectively cut dentin onthe outstroke. Without pressure, and in one or morepasses, SX is used to eliminate triangles of dentin,intentionally relocate the coronal aspect of a canalaway from external root concavities, and to shape thecoronal two-thirds of virtually any canal (Figure 8).9 Ingeneral, only about one-half to two-thirds of theoverall length of the active portion is carried belowany given orifice.

Scout the Apical One-ThirdWith the pulp chamber filled brimful with a viscouschelator, a size 10 file is generally used to scout,negotiate, and secure the apical one-third of a canal.Fortuitously, a pre-enlarged canal will more easilyenable dentists to direct a precurved size 10 file tolength (Figure 9). However, infrequently but onoccasion, it may be necessary to drop to a smallersize hand file to safely achieve length. Once a size10 file has reached length, it is gently, deliberately,and repeatedly worked, again using 0.5 to 1.0 mmultrashort vertical strokes, until it is completely loose.

Establish the Working LengthWorking length is established using radiographic imagesand/or an electronic apex locator. With experience, apexlocators can provide an accurate working lengthdetermination, even in canals that contain exudates orelectrolytes. However, it is appreciated that apex locators aremore reliable when used with a viscous chelator in a pre-enlarged canal. When the apical one-third of a canal has beenfully negotiated, working length is established (Figure 10). Topromote the biological and mechanical objectives for preparingcanals, working length corresponds to the radiographicterminus (RT), as the canal, by definition, will be open andpatent, apically.

Confirm PatencyPatency is confirmed by gently sliding a precurved SS size 10file to and minutely through the terminus of a canal (Figure 11).At this depth, ultrashort vertical strokes are continued until thisfile is completely loose. The RT is anatomically recognized to

be a point minutely beyond the cemento-dentinal junction(CDJ). Working a flexible, small-sized file to the RT serves toencourage the elimination of pulpal tissue, bacteria whenpresent, and dentinal mud. Keeping the terminus of a canalpatent discourages blocks, ledges, and perforations. It isillogical to assume that passing a small-sized file passively andminutely through the CDJ will predispose to any irreversibleharm, when one reflects on the healing capacity of thesupporting structures.

Verify the Glide PathAn apical glide path is verified and the canal termed securewhen a size 10 file can reproducibly slip, slide, and glidealong the length of the apical one-third of any given canal(Figure 12). On the contrary, there is no reproducible glidepath if the handle of a small-sized file must be manuallyreciprocated in order to carry a precurved size 10 file tolength. In these instances, the reader is invited to visit myWeb site (endoruddle.com) for information on how to


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Figure 7. PTG Auxiliary Shaping file (SX)is for radicular access and is utilized in abrushing manner, on the outstroke, to cutdentin between D6 and D9.

Figure 8. SX is used to remove trianglesof dentin, relocate canals away fromexternal root concavities, and producemore root-centered preparations.

Figure 9. In the presence of a viscous chelator, a precurved size 10 file ispassed through a pre-enlarged canal andutilized to negotiate the rest of the canal.

Figure 10. Working length is moreaccurately established in a pre-enlargedcanal.

prepare canals when there is no reproducible glidepath. When a size 10 file can reproducibly slide alongthe glide path and to length, then when necessary,this pathway is further expanded to a minimum of0.15 mm to more readily accommodate the tips ofmechanical shaping files.

Pre-Shape the Apical One-ThirdTraditionally, a rather stiff SS size 15 hand file hasbeen used to expand the terminal diameter of theglide path. Beyond stiffness, the other clinicalproblem associated with a size 15 file is the fact thatits D0 diameter is 50% bigger than the D0 diameterof the size 10 file. As such, a considerably stiffer andlarger size 15 hand file has long been associatedwith iatrogenic problems, especially when expandingthe apical one-third portion of the glide path inlonger, narrower, and more curved canals.Fortuitously, a metallurgically enhanced ProGlideroffers a safer, faster, and easier method to pre-shapethe apical one-third glide path.

Clinically, it is easy to move from a loose size 10file to a ProGlider, even though this represents atheoretical transition from 0.10 mm to 0.16 mm.Recall the size 10 file has a taper of 0.02 mm/mm,which means this file is 0.12 mm in diameter at D1.If the size 10 file is carried minutely beyond the CDJand to the RT, and gently worked until it is loose,then the canal, by definition, is a little larger than thefile itself. If a size 10 file is used as described, thenthe CDJ would be transitioned from 0.12 mm to atleast 0.13 mm in diameter. As such, the actualpercentage change between the size 10 file at D1and the ProGlider at D0 is a negligible 23%.

With the pulp chamber filled with NaOCl,ProGlider is inserted into a pre-enlarged and apicallysecured canal and allowed to passively andprogressively advance toward length. In longer,narrower, and more curved canals, the Pro Glider filemay bog down and resist advancement along theglide path. In these in stances, remove the file,irrigate, recapitulate with a size 10 file, then re-irrigate toflush out debris. In this manner, continue with the Pro Glider

and pre-shape the apical one-third of virtually anypreviously secured canal (Figure 13).


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Figure 11. Patency is confirmed whenthe size 10 file can gently andreproducibly slide to and minutelythrough the terminus of a canal.

Figure 12. A canal is termed securedwhen a size 10 file can reproduciblyslip, slide, and glide over the apicalone-third of a canal.

Figure 13. In a bath of NaOCl,ProGlider is utilized, in one or morepasses, to expand or pre-shape theglide path.

Figure 14. (a) PTG Shaping file No. 1(S1) is used with a brushing motion onthe outstroke and allowed to passivelyadvance inward along the glide path andto length. (b) Following S1, Shaping fileNo. 2 is used, as described for S1, untilworking length is reached.

a b

Figure 16. When the apical flutes of aPTG Finishing file are fully loaded withdentin, then the shape is cut and thefinishing criteria is fulfilled.

Figure 15. (a) PTG Finishing file No. 1(F1) is used in a brushing manner inone or more passes, until the workinglength is reached. (b) If the F1 apicalflutes are partially loaded, or not loadedat all, proceed with the Finishing file No.2 until working length is reached.

a b

Shape the Apical One-ThirdWhen the apical one-third of the canal has been securedand expanded to at least 0.15 mm, then the pulp chamberis filled brimful with NaOCl. The PTG sequence is to firstcarry the Shaping file No. 1, termed S1, to the full workinglength in one or more passes. Specifically, S1 is allowed tofloat into the canal and, before resistance, is used with abrushing action on the outstroke. A brush-cutting actioncreates lateral space and allows the bigger, stronger, andmore efficient blades to passively run deeper into thecanal.9 If S1 bogs down and ceases to passively advance,remove the file, then irrigate, recapitulate with a size 10 file,and re-irrigate. In this manner, continue with S1 until theterminus of the canal is reached (Figure 14).

Following S1, irrigate, recapitulate with a size 10 file, andre-irrigate. Proceed to Shaping file No. 2, termed S2, and usethis file in the exact same manner as just described for S1.Importantly, a brushing action facilitates shaping ca nals thatexhibit irregular shaped cross sections. S2 will typically move tolength in one or more passes depending on the length, diameter,and curvature of the canal (Figure 14). After removing any givenrotary file, irrigate, recapitulate with a size 10 file, then re-irrigate.After sequentially using S1 and S2 to the RT, particularly inmore curved canals, working length should be reconfirmed, asa more direct path to the terminus has been shaped.

Finish the Apical One-ThirdThe PTG Finishing files all have fixed tapers from D1 to D3,then decreasing percentage tapers from D4 to D16. Themost frequently used Finishing files are F1 (20/07), F2(25/08), and F3 (30/09). These PTG Finishing files have amaximum flute diameter at D16 of about 1.0 mm versus 1.32mm, 1.53 mm, and 1.77 mm, respectively, if their fixed taperswere to continue over the length of their active portions.Interestingly, this strategic design feature occurred more thana dozen years before the first report of the concept ofminimally invasive endodontics.7

The PTG F1 (20/07) is selected and passively used in abrushing manner to move deeper into the canal. If F1 ceasesto readily advance toward length, recognize its blades areloaded with debris, which, in turn, limits its capacity to engage,cut, and get pulled deeper into the canal. In these instances,remove the file, irrigate, recapitulate with a size 10 hand file,


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Figure 17a. This image reveals multiplanar shapes skillfully prepared with ProGlider and PTG. (Courtesy of Dr. ThomasV. McClammy; Scottsdale, Ariz.)

a

b

c

Figure 17b. This image demonstrates significant midrootcurvatures exquisitely shaped with PTG. (Courtesy of Dr.Jordan West; Tacoma, Wash.)

Figure 17c. This image shows the management of difficultapical curvatures utilizing PTG. (Courtesy of Dr. MichaelW. Nimmich; Sumter, SC.)

then re-irrigate. Continue with F1, in one or more passes, untilthe terminus is reached (Figure 15). When F1 achieves length,the instrument is removed, and its apical flutes are inspected.

Finishing CriteriaThe “Finishing Criteria” is fulfilled whenever 3 to 5 mm ofthe most apical flutes of any given PTG Finishing file arefully loaded with dentin. If the apical flutes of F1 are loadedwith dentin, then visual evidence supports that the shapehas been cut and is done. However, upon removing anygiven Finish ing file, the clinician may observe the apicalflutes are partially loaded or not loaded at all. If the apicalflutes of F1 are not fully loaded with dentin, then theclinician proceeds to the next sequential Finishing file, orF2 (25/08).

In a bath of fresh NaOCl, F2 is progressively carried tolength in one or more passes (Figure 15). Upon reachinglength, F2 is removed and the apical flutes are inspected. Ifits apical flutes are fully loaded, then visual evidenceconfirms the shape is done (Figure 16). If the apical flutesof F2 are partially loaded or not loaded at all, then continueto the PTG F3 Finishing file, or F4 or F5 as indicated. TheProTaper se quence is always the same and will producethe shapes that promote 3-D disinfection and filling rootcanal systems (Figure 17).

CLOSING COMMENTSA dentist who has never used PTU for preparing canalstypically loves the performance of PTG, as is. If a dentist isan experienced PTU user, then this colleague may preferthe PTU Shapers in that they offer a little more resistanceto lateral brushing; this attribute makes them feel moreefficient to some clinicians. However, any dentistperforming endodontics will benefit from gold metaltechnology, which enables gold medal shaping results.GPM and shaping canals are the sine qua non of 3-Ddisinfection and filling root canal systems.

REFERENCES1. Schilder H. Cleaning and shaping the root canal. Dent

Clin North Am. 1974;18:269-296.2. Ruddle CJ. Cleaning and shaping root canal systems.

In: Cohen S, Burns RC, eds. Pathways of the Pulp. 8thed. St. Louis, MO: Mosby; 2002:231-291.

3. Pasqualini D, Bianchi CC, Paolino DS, et al.Computed micro-tomographic evaluation of glide pathwith nickel-titanium rotary PathFile in maxillary firstmolars curved canals. J Endod. 2012;38:389-393.

4. Ruddle CJ, Machtou P, West JD. Endodontic canalpreparation: innovations in glide path managementand shaping canals. Dent Today. 2014;33:118-123.

5. Johnson E, Lloyd A, Kuttler S, et al. Comparisonbetween a novel nickel-titanium alloy and 508 nitinolon the cyclic fatigue life of ProFile 25/.04 rotaryinstruments. J Endod. 2008;34:1406-1409.

6. Berutti E, Cantatore G, Castellucci A, et al. Use ofnickel-titanium rotary PathFile to create the glide path:comparison with manual preflaring in simulated rootcanals. J Endod. 2009;35:408-412.

7. Ruddle CJ. The ProTaper endodontic system:geometries, features, and guidelines for use. DentToday. 2001;20:60-67.

8. West JD. The endodontic Glidepath: “Secret to rotarysafety.” Dent Today. 2010;29:86-93.

9. Ruddle CJ. The ProTaper technique. Endod Topics.2005;10:187-190.


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POST EXAMINATION QUESTIONS

1. As important as the actual mechanical attributes ofany given brand line is to fully understand the finalshape a file, or series of files, can produce.

a. True b. False

2. Coronal access objectives should focus on flaringand flattening the internal axial walls, yet recognizethat access to the underlying root canal system isoftentimes limited.

a. True b. False

3. When necessary, the terminus of any canal shouldbe expanded to 0.5 mm to confirm sufficient space isavailable to safely initiate mechanical shapingprocedures.

a. True b. False

4. The concept of pre-enlargement is the antithesis ofthe so-called crown-down technique.

a. True b. False

5. ProGlider utilizes M-Wire technology, which has beenshown to improve the resistance to cyclic fatigue bya staggering 400%.

a. True b. False

6. In coronally restrictive canals, after locating anygiven orifice, the pulp chamber may be filled brimfulwith a viscous chelator. It is virtually impossible,however, to insert a size 10 file into the coronalaspect of most canals.

a. True b. False

7. While apex locators can provide an accurate workinglength determination, this technology cannot be usedin canals containing exudates or electrolytes.

a. True b. False

8. A brush-cutting action creates lateral space andallows the bigger, stronger, and more efficient bladesto passively run deeper into the canal.

a. True b. False


8


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Documents

Shaping Complex Canals - dentalCEtoday.com · size of the access cavity is dictated by the position of the oriﬁces on the pulpal ﬂoor. The axial walls are extended laterally such