Cleaning and Shaping of the Root Canal Systemkhotanpublishing.com/UploadedFiles/PFiles/560545045d73486.pdf · The stereotypic pulpal defense reaction is hard-tissue deposition (Figs

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Chapter 9

Cleaning and Shaping of the Root Canal System

Ove A. Peters and Christine I. Peters

Outline

FRAMEWORK FOR ROOT CANALTREATMENTPathophysiology of Endodontic DiseaseDental AnatomyClinical Objectives

CLEANING AND SHAPING: TECHNICALISSUESHand and Engine-Driven Instruments

Broaches K-Files Hedström Files Gates-Glidden DrillsNickel-Titanium Rotary Instruments LightSpeed InstrumentsProFile GT FilesHERO 642ProTaper K3 FlexMaster RaCe Physical and Chemical Properties of NiTi

Alloys Motors and DevicesDisinfectants, Dentin Surface Modifiers,

and Lubricants

Sodium Hypochlorite ChlorhexidineIodine Potassium IodideMTAD Ethylenediamine Tetra-Acetic Acid Calcium Hydroxide Other Irrigants Lubricants

CLEANING AND SHAPING: CLINICALISSUESBiologic ObjectivesMechanical ObjectivesConcepts and Strategies

CANAL PREPARATION TECHNIQUESHand InstrumentationRotary Instrumentation

LightSpeed InstrumentProFile ProTaper Hybrid Techniques

Other Systems

CANAL CLEANING TECHNIQUESDisinfectionSmear layer management

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Cleaning and Shaping of the Root Canal System 291

FRAMEWORK FOR ROOT CANAL TREATMENT

Clinical endodontics encompasses a number of treat-ments, but perhaps the most important is treating pulpsand root canal systems (with or without periradicularpathosis of pulpal origin) so that patients can retaintheir natural teeth in function and esthetics. The treat-ment of traumatic dental injuries and prophylactic treat-ment of vital pulps to maintain vitality are differentfrom pulpectomies in which root canal instrumentationis required. However, endodontic therapy essentially is

directed toward one specific set of aims: to cure orprevent periradicular periodontitis.295

Routine orthograde root canal treatment is a pre-dictable and usually highly successful procedure both inrelatively straightforward (Fig. 9-1) and more difficultcases (Figs. 9-2 and 9-3). In recent studies and reviews,favorable outcome rates of up to 95% were reported forthe treatment of teeth diagnosed with irreversible pul-pitis22,62,90; favorable outcome rates of up to 85% werereported for necrotic teeth.61,91,200,207

To date, many treatment modalities, includingnickel-titanium (NiTi) rotary instruments, have not

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FFig. 9-1 Effect of routine root canal treatment of a mandibular molar. A, Preoperative radiograph of tooth #19 shows radiolucent lesionsadjacent to both mesial and distal root apices. B, Working length radiograph shows two separate root canals in the mesial root and twomerging canals in the distal root. C, Posttreatment radiograph after shaping of root canal systems with nickel-titanium rotary files and obtu-ration with thermoplasticized gutta-percha. D, Six-month recall radiograph after restoration of tooth #19 with an adhesively inserted fullceramic crown; some periradicular bone fill can be seen. E, One-year recall radiograph shows evidence of additional periradicular healing. F. Five-year recall radiograph; the tooth not only is periapically sound, but also clinically asymptomatic and fully functional.

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292 THE CORE SCIENCE OF ENDODONTICS

been shown to have a statistically relevant impact ontreatment outcomes.200 This poses a real problem in theage of evidence-based therapy, because a new therapeu-tic technique should provide a better result than stan-dard procedures in clinical tests. The small number ofrelevant prospective clinical studies is only partly offsetby numerous in vitro experiments. This chapter includespertinent information from such studies, as well asresults from our own experiments, because rotarynickel-titanium instruments have become widely usedadjuncts in root canal treatment.

Pathophysiology of Endodontic Disease

Many prospective and perioperative factors have beensuggested as links to favorable treatment outcomes in

endodontic therapy. Such factors include the patient’sage and gender, the position of the tooth in the arch,extension of the root canal filling, and the use of certaininterappointment dressings, such as calcium hydroxideCa(OH)2. The presence of a periradicular osseous lesion(i.e., “apical periodontitis”) appears to be a relevantprognostic factor that reduces the likelihood of a favor-able outcome for root canal treatment; however, lesionsize by itself is not an indication for endodontic surgery(see Chapter 20). Fig. 9-4 shows two cases in which largeosseous lesions were treated by orthograde approaches;at recall appointments, the teeth were asymptomatic,and a reduction in lesion size was evident in both cases.

Some may question whether lesions such as the onesin Fig. 9-4 are in fact cysts. Several studies have demon-strated that lesion size shows little correlation with the

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Fig. 9-2 Root canal treatment in a case of apical and interradicular pathosis. A, Preoperative radiograph of tooth #19 shows an inter-radicular lesion. B and C, Postoperative radiographs after root canal preparation and obturation. Note the lateral canal in the coronal third ofthe root canal. D and E, Two-month recall radiograph suggests rapid healing. (Courtesy Dr. H. Walsch.)

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incidence of radicular cysts34,151,181,184; only histologicexamination can prove whether a radiolucency is in facta cyst. True cysts are believed to heal only after surgicalenucleation,183 whereas the noncystic majority of apicalprocesses heal predictably by orthograde endodontictreatment without surgery. An orthograde approach,therefore, appears to be beneficial in clinically asymp-tomatic cases and should include recall appointmentsat appropriate intervals (see Chapter 24).

If clinical symptoms persist or begin after endodon-tic therapy, surgery may be performed in addition toorthograde root canal treatment. In the case shown inFig. 9-5, a large lesion that extended into the maxillarysinus and nasal cavity was treated surgically 1 week afterorthograde therapy of teeth #7 and #8, which includedremoval of two instrument fragments. The lesion wascompletely enucleated during surgery, and a tissuebiopsy specimen was submitted for histologic process-ing; the lesion was diagnosed as a radicular cyst. As

expected in this case, the patient reported discomfortafter surgery. This supports the preference for a non-surgical approach whenever possible.

When root canal therapy is part of a comprehensivetreatment plan, a favorable outcome for the root canalportion is a prime requirement. Extended bridgeworkand removable dentures depend on healthy periradicu-lar tissues, just as they depend on healthy marginal andapical periodontal tissues. Fig. 9-6 presents a case inwhich a removable denture seemed unavoidable at thefirst examination. After extractions and root canaltherapy were performed, small-unit, fixed partial den-tures were placed. These reconstructions remain fullyfunctional and allow this patient to benefit from thenatural dentition.

In summary, orthograde root canal treatment has ahigh degree of predictability both in normal andcomplex cases. Some limitations exist, but the potentialfor a favorable outcome is significant. As indicated pre-

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Fig. 9-3 Root canal treatment in a case with unusual and complicated anatomy. A, Preoperative radiograph of tooth #7 in a 12-year-oldboy shows a substantial periradicular lesion and evidence of additional radicular anatomy (i.e., a dens-in-dente type II according to Oehlers’classification).187 B, Working length radiograph shows three separate root canals. C, Posttreatment radiograph 21–2 months after shaping of theroot canal systems with a nickel-titanium rotary system aided by ultrasonically activated K-files and dressing with calcium hydroxide four timesfor about 2 weeks each. Note the substantial periradicular bone fill. D, One-year recall radiograph shows evidence of periradicular healing.E, Two-year recall radiograph shows sound periradicular tissues.

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viously, the shaping and cleaning performed as part ofroot canal treatment are directed against microbial chal-lenges to the root canal system.188 Microbes can breachdental hard-tissue barriers through several avenues, themost common being dental caries (Fig. 9-7).

Dental Anatomy

Pulpal reactions may be observed as soon as the diffu-sion barrier (the remaining dentin thickness) is suffi-ciently permeable for bacteria or their toxins to affectthe pulp35 (Fig. 9-7). Under experimental conditions,pulpal inflammation can be detected only a few hoursafter topical application of bacterial components toexposed dentin.28 In an established lesion, a bacterialecosystem evolves, with synergisms and antagonismsamong the microorganisms (see Chapter 15). Theseinteractions play an important role in the course of the

disease, when intraradicular biofilms develop and bac-teria invade dentinal tubules.159 Two key factors initiateand modify inflammatory reactions, such as the devel-opment of microabscesses in subodontoblastic regions:the penetration of bacterial components and the releaseand diffusion of inflammatory mediators.

The stereotypic pulpal defense reaction is hard-tissuedeposition (Figs. 9-7 and 9-8) by primary and second-ary odontoblasts.35 Hard tissue is laid down as aresponse to a stimulus (reactionary or reparative dentino-genesis) and thus takes place within a defined spatialrelationship to that stimulus, occurring slightly apical tothe lesion.

Hard-tissue deposition is a natural event with aging310

(secondary dentinogenesis), which creates a higher degreeof treatment difficulty in older patients. Clinicians notea radiographically detectable decrease in the size of thepulp space that occurs most often in the coronal regionsG

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DFig. 9-4 Potential of root canal treatment in cases of substantial periradicular destruction. A, Preoperative radiograph of teeth #8 and #9shows a large lesion. Neither tooth responded to cold tests. B, Two-year followup radiograph shows bone fill. The canals were shaped withrotary and hand instruments, and obturation was performed using laterally compacted gutta-percha with AH Plus as the sealer. C, Preoper-ative radiograph of tooth #4, which has a previously filled root canal; a large periradicular lesion and insufficient obturation can be seen. D, Two-year postoperative radiograph shows evidence of bony healing after nonsurgical retreatment. (A and B courtesy Dr. M. Zehnder; C andD courtesy Dr. F. Paqué.)

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but also can be seen in the more apical areas. This condition is not a contraindication to orthograde end-odontic therapy; however, it requires additional atten-tion to clinical procedures such as preenlargement andprebending of hand files (discussed later in the chapter).

The process of calcific metamorphosis is a response totraumatic injury.14 It is characterized by a reduction inthe size of both the radicular and coronal pulp spaces.Conversely, teeth with signs of hard-tissue depositioncaused by bacterial attack show an initial reduction ofpulp space size coronally, which may involve the pulpchamber and canal orifices (Fig. 9-7). This situationcalls for meticulous preparation of an access cavity andpreenlargement of canal orifices in a nondestructivemanner. Depending on the timing of inoculation andthe number of microbes, hard-tissue deposition alsomay occur more apically.145

Reparative dentin may form a diffusion barrier suffi-cient for the pulp to recover, depending on the severityof the bacterial challenge and the capability of thedefense mechanisms.163 Unfortunately, no consensusexists on the best therapy to allow this recovery tooccur.29

Further into the disease progress, and if the cariouslesion persists, bacteria may be present in sufficient

concentrations to induce pulpal inflammation. This istriggered by molecular signals (e.g., cytokines), whichare released from cells such as macrophages and neu-trophils well before microbes are actually present intra-pulpally (see Chapter 13). At this stage, with a diagnosisof reversible pulpitis, endodontic treatment may beavoidable, provided the source of the irritants isremoved.

To deliver adequate endodontic therapy, the clinicianmust understand that apical periodontitis is the end-point of a disease flow that in most cases originatescoronally, either with carious lesions or a traumatizedpulp (Fig. 9-7). As stated previously, opportunistic bacteria may invade dental hard tissue, and theirbyproducts eventually may reach the pulp space (seeChapter 15). Host response factors, such as the recruit-ment of neutrophil granulocytes and local developmentof neurogenic inflammation, act against microbial inva-sion, but this line of defense may succumb to the chal-lenge if the carious defect is not repaired. Then, aftermicroabscesses form, circulation changes occur; coronaland subsequently radicular pulp may become nonper-fused and thus necrotic.

At various points in this process, bacterial factorssuch as lipopolysaccharides and peptidoglycans134 can G

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B,C DFig. 9-5 Possibilities and limitations of orthograde endodontic therapy. In this case, a large lesion in the right maxilla was enucleated andhistologically diagnosed as a radicular cyst. A, Preoperative occlusal plane radiograph shows a large periradicular lesion in the right maxilla,as well as two separated instruments in tooth #7 (arrow). B, Postoperative periapical radiograph of tooth #7 and necrotic tooth #8, whichwere obturated after calcium hydroxide dressings had been placed for two weeks. Obturation was done with laterally compacted gutta-perchaand Roth’s 801 sealer. C, Two lentulo spiral fragments removed from tooth #7 (ruler gradation is 0.5 mm). D, Histologic slide shows bothrespiratory epithelium (arrow) and squamous epithelial lining and inflammatory cells, supporting the diagnosis. (C courtesy Dr. I. Hegyi.)

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reach periapical tissues through apical and accessoryforamina. Zones of bone resorption (appearing as radi-olucencies) may develop, depending on the balancebetween microbial virulence factors and hostdefenses.272 The development of apical periodontitis isassociated with a significantly less encouraging progno-sis after orthograde endodontic treatment.62,261,263

One school of thought emphasizes the importanceto successful endodontic therapy of cleaning and fillinglateral and accessory canals. 227,314 Clinical radiographsof artfully done cases support this position; the contri-bution of accessory canals to lesion development incertain cases seems highly likely (Fig. 9-2). However,this pathogenesis depends on the volume of accessorycanals and the amount of bacteria harbored in them.Another subject of controversy is the clinical importanceand mechanisms of dentinal tubule infection158,159,197

with bacteria and fungi (Fig. 9-9).In most cases lesions are associated with the main

root canal systems (Figs. 9-1 and 9-3 to 9-5) and formperiapically around the main foramina. The main canalunquestionably has the highest bacterial load, andimportant studies link reduction of the viable intracanalbacterial load to favorable outcomes for endodontictherapy.138,196,261 Therefore a primary aim of all endodon-tic procedures, and most notably of cleaning andshaping, is to remove canal contents, specifically infec-tive microorganisms.2

Clinical Objectives

A wide spectrum of possible strategies exists for attaining the goal of removing the canal contents andeliminating infection. Lussi et al165 introduced a mini-mally invasive approach to removing canal contents and accomplishing disinfection that did not involve theuse of a file (the noninstrumentation technique [NIT]).This system consisted of a pump, a hose, and a specialvalve that was cemented into the access cavity (Fig. 9-10, A) to provide oscillation of irrigation solutions (1%to 3% sodium hypochlorite [NaOCl]) at a reduced pres-sure. Although several in vitro studies164,166,167 demon-strated that canals can be cleaned and subsequentlyfilled using this system (Fig. 9-10, B and C), preliminaryclinical results have not been as convincing (Fig. 9-10,D).15

At the opposite end of the spectrum is a treatmenttechnique that essentially removes all intraradicularinfection through extraction of the tooth in question(Fig. 9-10, C). Almost invariably, periradicular lesionsheal after extraction of the involved tooth.

Clinical endodontic therapy takes place somewherealong this spectrum of treatment strategies. This isreflected in some of the controversies that surround thecleaning and shaping process, such as how large theapical preparation should be and what are the correctdiameter, length, and taper.135G

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Fig. 9-6 Root canal therapy as part of a comprehensive treat-ment plan. The patient, who was recovering from intravenous drugaddiction, requested restorative dental treatment. Because of exten-sive decay several teeth had to be extracted, and nine teeth weretreated endodontically. Root canal treatment was aided by nickel-titanium rotary instruments, and obturation was done with lateralcompaction of gutta-percha and AH26 as the sealer. Microsurgicalretrograde therapy was performed on tooth #8, and the distobuc-cal root of #14 had to be resected. Metal-free adhesively lutedrestorations were placed, and missing mandibular teeth werereplaced by implants. A, Preoperative intraoral status, showing oralneglect. B, Postoperative intraoral status at 4-year followup,showing fully functional, metal-free, tooth-colored reconstructions.C, Panoramic radiograph at 4-year recall shows sound periradiculartissues in relation to endodontically treated teeth. (Restorationsdone by Dr. Till N. Göhring.)

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The foundation of the endodontic treatment plan isan adequate diagnostic process (see Chapter 1), whichincludes obtaining diagnostic radiographs from variousangles. Also, the restorability and periodontal status ofteeth to be treated endodontically must be determined;in some cases buildups or crown lengthening is requiredfor preendodontic restoration to allow proper isolation,to create pulp chambers that retain irrigants, and to facil-itate interappointment temporary restorations. In manycases the existing restoration may have to be removed so

that an adequate diagnosis can be made and the imme-diate cause of endodontic treatment can be assessed.1

Once the decision has been made to initiateendodontic treatment, the clinician must integrate hisor her knowledge of dental anatomy, immunology, andbioengineering science with clinical information. Theintent of this chapter is to assist clinicians with that taskand to provide a much-condensed background in radic-ular anatomy, pulpal pathophysiology, and nickel-titanium metallurgy. G

Carious Lesion

Bacterial Invasion

Periapical Granuloma

Endodontic Disease Process

Fig. 9-7 Progression of pulpal disease and the development of periradicular pathosis. A carious lesion leads to contact of toxins andmicrobes with the coronal pulp, resulting in inflammation and infection. The stereotypic defense reaction of dental pulp then occurs: hard-tissue deposition. This reaction may lead to repair or to additional hard-tissue deposition (e.g., as calcific metamorphosis). The next step maybe formation of microabscesses, changes in circulation during inflammation, and ultimately progression of infection into the radicular pulpspace. Finally, periradicular osseous lesions may develop if the bacterial challenge persists. (Courtesy Dr. H.-U. Luder and T. Häusler.)

A BFig. 9-8 Evidence of coronal hard-tissue deposition. A, Periapical radiograph of tooth #19 shows evidence of reduced coronal and radic-ular pulp space. B, Intraoral photograph, taken through an operating microscope (¥25), of access cavity of the tooth shown in A; note thecalcific metamorphosis.

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Endodontic therapy has been compared to a chain,and it has rightfully been pointed out that the chain isonly as strong as each individual link. For the purposesof this chapter, shaping and cleaning of the root canalsystem is considered a decisive link, because shapingdetermines the efficacy of subsequent procedures. Itincludes mechanical debridement, the creation of spacefor the delivery of medicaments, and optimized canalgeometries for adequate obturation.198 These tasks areattempted within a complex anatomic framework, asrecognized in the early twentieth century by WalterHess124 (Fig. 9-11) (see Chapter 7).

Unfortunately, canal preparation results are adverselyaffected by the highly variable root canalanatomy.9,10,126,180,205 This fact is especially true for con-ventional hand instruments and to a lesser degree formost nickel-titanium rotary instruments.31,198 Thereforethe radicular anatomy is briefly reviewed as it pertainsto cleaning and shaping.

Root canal curvature can be assessed clinically fromradiographs, preferably taken from various angles.

However, it is well documented that curves in themesiodistal plane often are greater than those in themore readily accessible buccooral plane.66,208 In vitro afull account of three-dimensional canal anatomy can beseen with interactive micro–computed tomographic(mCT) reconstructions (Figs. 9-12 and 9-13).

The clinician must understand the five commonlyencountered canal paths (i.e., canals that merge, curve,recurve, dilacerate, or divide).227 All five situations arerisk factors for file breakage and should be carefullyevaluated, as is done for more basic considerations suchas the estimated canal length, position of the primarycurve, canal diameter, and apical topography.

Early anatomic studies108,109,148 evaluated the positionand topography of the apical foramina and the positionof the apical constriction. These studies found that thephysiologic foramen, or canal terminus, was located up to1mm coronal to the anatomic apex, or root tip. Thisobservation has been confirmed by later studies.81,176

Clinically, the landmark detected from radiographs(the radiographic apex) does not necessarily coincidewith the anatomic apex because of projection artifacts.Taken together, these observations suggest that shapingto the radiographic apex is likely to produce overin-strumentation past the apical foramen, with possibleclinical sequelae of postoperative pain and inoculationof microorganisms into periapical spaces.27,29,84,111

Foramen diameter was also an issue in both early109,148

and more recent studies.41,81,176,273 The smallest canaldiameter, called the apical constriction, was located 0.5 to0.7mm coronal to the canal terminus.109,148 A wide rangeof diameters has been reported in that region, from 0.2to about 1 mm41,141-143,148,176; the concept of a single apicalconstriction has also been challenged.81 Moreover,studies have shown that clinicians usually underestimateapical dimensions.315 Clearly, the apical anatomy pres-ents the clinician with major challenges (Fig. 9-14), suchas apically dividing canals, nonround cross sections, anddeltalike configurations. In addition, canal cross sectionsthat are wide buccolingually314 are difficult to instrumentwith rotary techniques.

The clinician must choose the strategies, instruments,and devices to deal with these challenges and to controlthe preparation shape, length, and width precisely. Thisallows the practitioner to use endodontic therapy toaddress acute (Fig. 9-15) and chronic (Fig. 9-16) formsof the disease processes described previously. Recallradiographs taken at appropriate intervals will demon-strate longevity and favorable outcomes (see Figs. 9-1 to 9-4, 9-6, and 9-16) if clinical objectives are maintained(Box 9-1).

CLEANING AND SHAPING: TECHNICAL ISSUES

Because several technical issues arise with the instru-ments and devices used for cleaning and shaping, a

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Fig. 9-9 Presence of microorganisms inside the main root canal and dentinal tubules. A, Scanning electron micrograph of aroot canal surface shows a confluent layer of rod-shaped microbes.(¥3000.) B, Scanning electron micrograph of a fractured root with a thick smear layer and fungi in the main root canal and denti-nal tubules. (A courtesy Professor C. Koçkapan; B courtesy Dr. T. Waltimo.)

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Fig. 9-10 Spectrum of strategies for accomplishing the primary aim of root canal treatment: elimination of infection. A, Schematic diagramof minimally invasive therapy using the noninstrumentation technique. B, Example of teeth cleaned in vitro using NIT. Note the clean intra-canal surface, which is free of adhering tissue remnants. C and D, Examples of teeth cleaned in vivo and later extracted to investigate theclinical effects of NIT. Note the relatively clean, tissue-free canal space in C and the significant tissue revealed by rhodamin B staining in D.E and F, Course of maximally invasive therapy; apically involved tooth #30 was extracted, effectively removing the source of periradicularinflammation. (A and B courtesy Professor A. Lussi; C and D courtesy Professor T. Attin; E and F courtesy Dr. T. Kaya.)

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short review of these products is provided here (also seeChapter 8). A vast array of instruments, both hand-heldand engine-driven, is available for root canal prepara-tion. Up to the last decade of the past century, endodon-tic instruments were manufactured from stainless steel.With the advent of nickel-titanium,250 instrumentdesigns began to vary in terms of taper, length of cutting

blades, and tip design. Files traditionally have been pro-duced according to empiric designs, and most instru-ments still are devised by individual clinicians ratherthan developed through an evidence-based approach.Similar to the development of composite resins inrestorative dentistry, the development of new files is afast and market-driven process. With new versionsG

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Fig. 9-11 Panel of 36 anatomic preparations of maxillary molars from the classic work by Professor Walter Hess of Zurich. Note the overallvariability of root canal systems and the decrease of canal dimensions with age. (From Hess W: The anatomy of the root canals of teeth of thepermanent dentition, London, 1925, John Bale, Sons & Danielsson.)

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Fig. 9-12 Micro-computed tomographic scans of dentalanatomy (36 mm resolution). A, Clinical view of tooth #9 shows twoaccessory canals and an apical bifurcation. B, Mesiodistal view ofthe tooth shown in A. C, Working length radiograph with files placedin both apical canal aspects.

A BFig. 9-13 Micro-computed tomographic scans of more compli-cated dental anatomy (36 mm resolution). A, Clinical view of tooth#3 shows a fine mesiobuccal and distobuccal canal system withadditional anatomy in all three roots. B, Mesiodistal view of thetooth shown in A.

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rapidly becoming available, the clinician may find it dif-ficult to pick the file and technique most suitable for anindividual case. Practitioners must always bear in mindthat all file systems have benefits and weaknesses. Ulti-mately, clinical experience, handling properties, usagesafety, and case outcomes, rather than marketing or theinventor’s name, should decide the fate of a particulardesign.

Hand and Engine-Driven Instruments

Hand instruments have been in clinical use for almost100 years, and they still are an integral part of cleaningand shaping procedures. A norm established by theAmerican Dental Association (ADA) and the Interna-tional Standards Organization (ISO)13,131 sets the stan- G

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B CFig. 9-14 Micro-computed tomographic scan of anatomy of the apical 5 mm of a mesiobuccal root (8 mm resolution). A and B, Three-dimensional reconstruction of outer contour and root canal systems. C, Cross sections 0.5 mm apart.

Box 9-1 Basic Objectives in Cleaningand Shaping

The primary objectives in cleaning and shaping the rootcanal system are to:• Remove infected soft and hard tissue• Give disinfecting irrigants access to the apical canal

space• Create space for the delivery of medicaments and

subsequent obturation• Retain the integrity of radicular structures

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dards for broaches, K-type files and reamers, Hedströmfiles, and paste carries; however, the term ISO-normedinstruments currently is used mainly for K-files (Fig. 9-17). One important feature of these instruments is adefined increase in diameter of 0.05mm or 0.1mm,depending on the instrument size (Fig. 9-18).

Broaches Barbed broaches are produced in a variety of sizes andcolor codes. They are manufactured by cutting sharp,coronally angulated barbs into metal wire blanks.Broaches are intended to remove vital pulp from rootcanals, and in cases of mild inflammation, they work well for severing pulp at the constriction level in toto. The use of broaches has declined since theadvent of NiTi rotary shaping instruments, but broach-ing occasionally may be useful for expediting proce-dures and for removing materials (e.g., cotton pellets)from canals.

K-Files K-files were manufactured by twisting square or trian-gular metal blanks along their long axis, producing

partly horizontal cutting blades (Fig. 9-19). Noncuttingtips, also called Batt tips, are created by grinding andsmoothing the apical end of the instrument (see Fig. 9-19). Roane and Powell223 introduced a modifiedshape, the Flex-R file, which was manufactured fully bygrinding so that the transitional angles were smoothedlaterally between the tip and the instrument’s workingparts. Similar techniques are required to manufactureNiTi K-files,281 such as the NiTi-Flex (Dentsply Maillefer, Ballaigues, Switzerland). NiTi K-files are extremely flex-ible and are especially useful for apical enlargement insevere apical curves. They can be precurved but onlywith strong overbending; this subjects the file to excessstrain and should be done carefully. Because of theirflexibility, the smaller NiTi files (sizes up to #25) are oflimited use.

Cross-sectional analysis of a K-file reveals why this design allows careful application of clockwise andcounterclockwise rotational and translational workingstrokes. ISO-normed K- and Hedström files are availablein different lengths (21, 25, and 31 mm), but all have a16mm long section of cutting flutes (Fig. 9-17). Thecross-sectional diameter at the first rake angle of any fileG

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Fig. 9-15 Sinus tract as a sign of a chronic apical abscess and effect of routine root canal treatment. A, Intraoral photograph of left max-illary region with draining sinus tract (arrow) periapical to tooth #14. B, Preoperative radiograph with gutta-percha point positioned in thesinus tract, pointing toward the distobuccal root of #14. C, Finished root canal fillings after 2 weeks of calcium hydroxide dressing. D, Intra-oral photograph of the same region as in A, showing that the sinus tract had closed by the time obturation was performed.

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is labeled D0. The point 1mm coronal to D0 is D1, thepoint 2mm coronal to D0 is D2, and so on up to D16.The D16 point is the largest diameter of an ISO-normedinstrument. Each file derives its numeric name from the diameter at D0 and is assigned a specific color code(see Fig. 9-17).

Another aspect of ISO files is the standard taper of0.32mm over 16mm of cutting blades, or 0.02mmincrease in diameter per millimeter of length (#.02taper) (see Fig. 9-17). Thus a size #10 instrument has adiameter of 0.1mm at D0 and a corresponding diame-

ter of 0.42mm at D16 [0.1mm + (16 ¥ 0.02 mm)]. Fora size #50 instrument, the diameters are 0.5mm at D0

and 0.82mm at D16.The tip size increases by 0.05mm for file sizes #10 to

#60; for sizes #60 to #140, the absolute increase is0.1mm (see Fig. 9-18). Recalculation of these diameterincrements into relative steps (in percentages) revealsdramatic differences: the step from size #10 to #15 is50%, whereas the increase from size #55 to #60 is lessthan one fifth of that change (Fig. 9-18).

In very small files (sizes #6 to #10), the problem ispartly resolved by several key points: (1) apical dimen-sions are such that a size #6 file does not significantlyremove dentin other than in severely calcified cases; (2) a size #8 file taken 0.5 to 1mm long, to establishpatency (discussed later in the chapter), contacts thedesired endpoint of the preparation with a diameterapproaching the tip size of a #10 file; (3) similarly,placing a size #10 file just minutely through the forameneases the way for passive insertion of the subsequent#15 file to full length.227

The ISO specifications inadvertently complicated thecleaning and shaping of root canal systems. The ISO-normed design is a simplification that has specific dis-advantages, and it may explain the clinical observationthat enlarging from size #10 to #15 is more difficult thanthe step from size #55 to #60. The introduction of theGolden Medium files (Dentsply Maillefer), which havetip sizes between the ISO-stipulated diameters, seemedto solve the problem. However, their use is not thatimportant clinically, because the approved machiningtolerance of ± 0.02mm negates the intended advantage.Moreover, although ± 0.02mm tolerance is stipulated bythe ISO norm (see Fig. 9-17), many manufacturers donot adhere to it.139,245,274,335

A subsequent modification involved tips with a con-stant percentage of diameter increments, the Series 29.The first ProFile instruments (Dentsply–Tulsa, Tulsa,OK) followed this design with a nominal diameterincrease of 29%. This sizing pattern creates smallerinstruments that carry less of a workload. However, theintended advantage is offset by larger diameters, becausethe 29% increase between successive files is actuallygreater than the percentage change found in the ISO fileseries.

Hedström Files Hedström files are milled from round, stainless steelblanks. They are very efficient for translational strokes,237

but rotational working movements are strongly discour-aged because of the possibility of fracture. Hedströmfiles up to size #25 can be efficiently used to relocatecanal orifices and, with adequate filing strokes, toremove overhangs. Similarly, wide oval canals can beinstrumented with Hedström files as well as with rotaryinstruments. On the other hand, overzealous filing canlead to considerable thinning of the radicular wall and G

A,B

D,E F

C

Fig. 9-16 Relationship of radicular anatomy and endodonticdisease as shown by filled accessory canals. A, Working length radi-ograph of tooth #13 shows lesions mesially and distally but not api-cally. B, Posttreatment radiograph shows the accessory anatomy. C,Six-month recall radiograph before placement of the restoration. D,Two-year recall radiograph after resection of the mesiobuccal rootof tooth #14 and placement of a fixed partial denture. Excess sealerappears to have been resorbed, forming a distal residual lesion. E,Four-year recall radiograph shows almost complete bone fill. F,Seven-year recall radiograph; tooth #14 is radiologically sound andclinically within normal limits.

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strip perforations (Fig. 9-20). As with stainless steel K-files, Hedström files should be single-use instruments.269

Gates-Glidden DrillsGates-Glidden (GG) drills are important instrumentsthat have been used for more than 100 years withoutnoteworthy design changes. These instruments, espe-cially the nickel-titanium FlexoGates model (DentsplyMaillefer),101 usually work well for preenlargement ofcoronal canal areas.77,174 However, when misused, GGdrills can dramatically reduce radicular wall thickness.100,132,161

GG instruments are manufactured in a set and num-bered 1 to 6 (with corresponding diameters of 0.5 to1.5 mm); the number of rings on the shank identifies

the specific drill size. GG instruments are available invarious lengths and made by several manufacturers.Each instrument has a long, thin shaft with parallelwalls and a short cutting head. Because of their designand physical properties,40 GG drills are side-cuttinginstruments with safety tips; they can be used to cutdentin as they are withdrawn from the canal (i.e., on theoutstroke).227 Used this way, their cutting action candeliberately be directed away from external root con-cavities in single-rooted and furcated teeth.3 GG instru-ments should be used only in the straight portions ofthe canal, and they should be used serially and passively.311

Two procedural sequences have been proposed: withthe step-down technique, the clinician starts with a largeG

15 20 25 30 35 40 Normed instrument tip sizes

Taper 0.02mm/mm

Length of working part 16mm

Color-coded instrument handles

Fig. 9-17 Schematic drawing of an ISO-normed hand instrument size #35. Instrument tip sizing, taper, and handle colors are regulatedby the ISO/ANSI/ADA norm.

0.3 % Increase

Absolute increase in mm

100

90

80

70

60

50

40

30

20

10

0

0.2

0.1

08 10 15

[mm

]

[%]

20 25 30 35 40Instrument No. (ISO)

45 50 55 60 70 80 90 100

Fig. 9-18 Increase in tip diameter in absolute figures and in relation to the smaller file size. Note the particularly large increase from size#10 to size #15.

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tive orifice and progression for about 1 mm. The sub-sequent smaller instruments progress deeper into thecanal until the coronal third has been preenlarged. Thistechnique efficiently opens root canal orifices and worksbest when canals exit the access cavity without severeangulations. Opened orifices simplify subsequent clean-ing and shaping procedures and help to establish asmooth glide path from the access cavity into the rootcanal system.

With the step-back approach, a small GG instrumentis introduced into the canal and dentin is removed onthe outstroke. This process is repeated with the nextlarger GG instrument, which is again worked shorterthan the preceding smaller one. In this way, the coronalthird of the root canal is enlarged and dentin overhangsare removed.

As stated earlier, when used adequately GG instru-ments are inexpensive, safe, and clinically beneficialtools. High revolutions per minute (rpm), excessivepressure, an incorrect angle of insertion, and the use ofGG instruments to aggressively drill into canals haveresulted in mishaps, such as strip perforation. Also, GGinstruments may fracture when used in curved canalareas because of cyclic fatigue, and the short cuttingheads may fracture with high torsional loads. Gates-Glidden drills may be used safely and to their fullestpotential at 750 to 1500 rpm. As with nickel-titaniumrotary instruments, GG drills work best when used inelectric gear reduction handpieces rather than with airmotors.

Nickel-Titanium Rotary Instruments Since the early 1990s, several instrument systems man-ufactured from nickel-titanium have been introducedinto endodontic practice. The specific design character-istics vary, such as tip sizing, taper, cross section, helixangle, and pitch (Fig. 9-21). Some of the early systemshave been removed from the market or play only minorroles; others, such as LightSpeed (LightSpeed Technolo-gies, San Antonio, TX) and ProFile (Dentsply–Tulsa,Dentsply Maillefer), are still widely used. New designscontinually are produced, but the extent to which, ifany, clinical outcomes will depend on design character-istics is difficult to forecast.200

Most of the instruments described in this section aremanufactured by a grinding process, although some areproduced by laser etching. Precision at the surfacequality is not really at a high level, whereas the toler-ances are. Surface quality also is an important detail(see Fig. 9-21), because cracks that arise from superficialdefects play a role in instrument fracture.11 Superficialdefects such as metal flash and rollover are common inunused NiTi instruments.83,170,336

Attempts have been made to improve surface qualityby electropolishing the surface and by coating it withtitanium nitride.217,235 The latter process also seems tohave a beneficial effect on cutting efficiency.235 G

A

B

Fig. 9-19 Flute geometry and tip configuration of a hand file(insert) and a NiTi rotary instrument. A, K-file with sharp cuttingedges (arrow) and Batt tip (arrowhead). B, GT rotary file withrounded, noncutting tip (arrowhead), smooth transition, andguiding radial lands (arrow).

Fig. 9-20 Result of an overenthusiastic attempt at root canaltreatment of a maxillary second molar with large, stainless steel files.Multiple strip perforations occurred; consequently, the tooth had tobe extracted.

drill and progresses to smaller ones; conversely, with thestep-back technique, the clinician starts with a smalldrill and progresses to larger ones. With the step-downapproach, the clinician must select a GG instrumentwith a diameter that allows introduction into the respec-

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In essence, two properties of the NiTi alloy are of par-ticular interest in endodontics: superelasticity (Fig. 9-22) and high resistance to cyclic fatigue (discussedlater). These two properties allow continuously rotatinginstruments to be used successfully in curved rootcanals. Many variables and physical properties influencethe clinical performance of NiTi rotaries.146,199,250,281

Much of what is known about NiTi instruments,including reasons for instrument fracture18 and instru-ment sequences, has been gleaned from clinical prac-tice. In vitro research continues to clarify therelationship between NiTi metallurgy and instrumentperformance, but already NiTi rotary instruments havebecome an important adjunct in endodontics.198

NiTi rotary instruments have substantially reducedthe incidence of several clinical problems, such asblocks, ledges, transportation, and perforation.However, they also have a tendency to fracture moreeasily than hand instruments. The clinical problemscited above do not by themselves predispose a case to

posttreatment disease; rather, they limit the access ofdisinfecting irrigants to the root canal system, prevent-ing sufficient elimination of microorganisms.115

The following sections describe the instruments mostwidely used in the United States and Europe for rootcanal preparation. Most basic strategies apply to all NiTirotary instruments, regardless of the specific design orbrand. However, three design groups need to be ana-lyzed separately: group I, the LightSpeed; group II,rotary instruments with #.04 and #.06 tapers, whichincludes the ProFile and many other models; and groupIII, rotary instruments with specific design changes, suchas the ProTaper (Dentsply Maillefer) and RaCe (FKG, LaChaux-de-Fonds, Switzerland).

LightSpeed InstrumentsThe LightSpeed file, developed by Dr. Steve Senia andDr. William Wildey in the early 1990s, was introducedas an instrument different from all others because of itslong, thin, noncutting shaft (Fig. 9-23) and 0.25 to2mm anterior cutting part. A full set consists of 25instruments in sizes #20 to #100, including half sizes(e.g., 22.5, 27.5).

The recommended working speed for LightSpeedinstruments is 1500 to 2000 rpm, and they should beused with minimal torque.249

The cross sections of the LightSpeed’s cutting partshow three round excavations, the U-shape designcommon to many earlier NiTi instruments (Figs. 9-23and 9-24). Because of the relatively thin noncuttingshaft, LightSpeed instruments are considerably moreflexible than any other instrument on the market. Inaddition, cyclic fatigue is lower than with all otherinstruments, allowing the use of higher rpm speeds. AllLightSpeed instruments feature a noncutting round tip;tip length increases with instrument size to compensatefor decreasing flexibility.

The LightSpeed’s predecessor, the Canal Master-U,had the same general design but was used as a handinstrument. LightSpeed’s manufacturer still recom-mends some hand use of its instruments, specifically fordetermining canal diameter. In general, the LightSpeedsystem requires a specific instrument sequence toproduce a tapered shape that facilitates obturation witha gutta-percha cone or with LightSpeed’s proprietaryobturation system.

The LightSpeed is a widely researched NiTi rotaryinstrument, and most reports have found that thesystem has a low incidence of canal transportation andpreparation errors.* Loss of working length wasminimal in most of these studies.

ProFile The ProFile system was introduced by Dr. Ben Johnsonin 1994. In contrast to the LightSpeed, with its thin, flex-ible shaft, the ProFile has an increased taper compared

G

�

p

rl

c

u

A

BFig. 9-21 Design characteristics of nickel-titanium rotary instru-ments. A, Lateral view showing the details of the helix angle, pitch(p), and the presence of guiding areas, or radial lands (rl). (Scan-ning electron micrograph [SEM], ¥25.) B, Ground working part ofthe instrument in A, showing U-shaped excavations and the dimen-sion of the instrument core (c).

*References 99, 202, 205, 212, 252, 253, 282, and 283.

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G

A,B CFig. 9-22 Deformation of endodontic instruments manufactured from nickel-titanium alloy. A and B, Intact and plastically deformed ProFileinstruments (arrows indicates areas of permanent deformation). C, ProFile instrument placed on a mirror to illustrate elastic behavior.

2mm

A B

C

Fig. 9-23 Design features of a LightSpeed instrument. A, Lateral view. (SEM, ¥50.) B, Cross section. (SEM, ¥200.) C, Lateral view. D, Designspecifications.

with conventional hand instruments. The ProFile firstwas sold as a series of 29 hand instruments in #.02 taper,but it soon became available in #.04 and #.06 conicity(see Fig. 9-24). The tips of the ProFile Series 29 rotaryinstruments (Dentsply–Tulsa) had a constant propor-tion of diameter increments (29%). Because of the non-standardized diameters, obturation was performed withnonstandardized gutta-percha cones, using either lateralcompaction or thermoplastic obturation of gutta-percha

(see Chapter 10). Later, another ProFile series (DentsplyMaillefer) was developed and marketed in Europe. Thisversion featured tip sizes similar to those of ISO-normed instruments. This set was believed to betteraccommodate standardized gutta-percha cones, whichare predominantly used in Europe. Subsequently,instruments with even greater tapers and 19mm lengthswere introduced, and recently a #.02 variant was added(see Fig. 9-24).

No. ofinstruments/set

25

Tip sizes

20-140

Sizeincrements

2, 5From #60: 5From #70: 10

r.p.m.(recommended)

1500-2000,very low axialforce, low torque

Lengths

21, 25,31 mm

D

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Cross sections of a ProFile instrument show a U-shapedesign with radial lands and a parallel central core.Lateral views show a 20-degree helix angle, a constantpitch, and bullet-shaped, noncutting tips. Together witha neutral or slightly negative rake angle, this configura-tion ensures a reaming or scraping action on dentinrather than cutting. Also, debris is transported coronallyand is effectively removed from the root canals.

The recommended rotational speed for ProFileinstruments is 150 to 300 rpm, and to ensure a constantrpm level, the preferred means is electrical motors withgear reduction rather than air-driven motors.

ProFile instruments shaped canals without majorpreparation errors in a number of in vitro investiga-tions.* A slight improvement in canal shape was notedwhen size #.04 and #.06 tapered instruments were usedin an alternating fashion.44 Loss of working length didnot exceed 0.5 mm44-46,285,286 and was not affected by theuse of size #.06 instruments.44

GT FilesThe Greater Taper file, or GT file (Fig. 9-25), was intro-duced by Dr. Buchanan in 1994. This instrument also

incorporates the U-file design. The GT system was firstproduced as a set of four hand-operated files and lateras engine-driven files. The instruments came in fourtapers (#.06, #.08, #.10, and #.12), and the maximumdiameter of the working part was 1 mm. This decreasedthe length of the cutting flutes and increased the taper.The instruments had a variable pitch and an increasingnumber of flutes in progression to the tip; the apicalinstrument diameter was 0.2 mm. Instrument tips werenoncutting and rounded.

The GT set subsequently was modified to accommo-date a wider range of apical sizes. The current setincludes instruments of three apical diameters: 0.2, 0.3, and 0.4mm (Fig. 9-25). The tapers also were modified and now are available in #.04, #.06, #.08 and#.10. In addition, accessory files with a #.12 taper areavailable in sizes #35, #50, #70, and #90. The maximumdiameter in these files is 1.5 mm, similar to that of a #6GG. The recommended rotational speed for GT files is350 rpm, and the instrument should be used withminimal apical force to avoid fracture of the tip.

Studies on GT files found that the prepared shapestayed centered and was achieved with few proceduralerrors.100,121,206,210,331 mCT comparisons showed that GTfiles machined statistically similar canal wall areas com-G

2mm

A B

C

Fig. 9-24 Design features of a ProFile instrument. A, Lateral view. (SEM, ¥50.) B, Cross section (SEM, ¥200.) C, Lateral view. D, Designspecifications. *Note that ProFile tip sizes do not always correspond to ISO sizes; for example, an instrument designated size #25 in fact hasa somewhat smaller tip diameter.

*References 44-46, 147, 202, 205, 284, and 285.


OrificeShapers: 6

ProFile .06: 6

ProFile .04: 9

ProFile .02: 6

ProfileSeries 29

Tip sizes

20-80

15-40

15-90

15-45

13-100

Sizeincrements

10; from60: 20

5

5; from#45: 15;from #60: 30

5

Varies, 29%

r.p.m.(recommended)

150 to 350,low apical force,torque tofracture andworking torquedependent oninstrument size

Lengths

19 mm

21 mm,25 mm,some31 mm

21 mm,25 mm D

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pared with ProFile and LightSpeed preparations.206

These walls were homogeneously machined andsmooth.191,331

HERO 642First-generation rotary systems had neutral or slightlynegative rake angles. Second-generation systems weredesigned with positive rake angles, which gave themgreater cutting efficiency. HERO instruments(MicroMega, Besançon, France) are an example of asecond-generation system.

Cross sections of a HERO instrument show geome-tries similar to those of an H-file without radial lands(Fig. 9-26). Tapers of #.02, #.04, and #.06 are availablein sizes ranging from #20 to #45. The instruments arerelatively flexible (the acronym HERO stands for highelasticity in rotation) but maintain an even distributionof force into the cutting areas.296,297 HERO instrumentshave a progressive flute pitch and a noncutting, passivetip, similar to other NiTi rotary systems. The instru-ments are coded by handle color.

Research with HERO files indicates a shaping poten-tial similar to that of the FlexMaster127 (Dentsply VDW,Munich) and the ProFile,97 although in one study theHERO induced more changes in cross-sectionalanatomy.105 HERO instruments also were found to causesome aberrations when used in simulated canals with

acute curves282 but were safer than Quantec SC instru-ments (Analytic Endodontics, Orange, CA).130

ProTaper The ProTaper system is based on a unique concept andcomprises just six instruments, three shaping files andthree finishing files. These instruments were designed byDr. Cliff Ruddle, Dr. John West, and Dr. Pierre Machtou.The cross section of the ProTaper shows a modified K-type file with sharp cutting edges and no radial lands(Fig. 9-27); this creates a stable core and sufficient flex-ibility for the smaller files. The cross section of finish-ing file F3 is slightly relieved for increased flexibility. Theunique design factor is the varying tapers along theinstruments’ long axes. The three shaping files havetapers that increase coronally, and the reverse pattern isseen in the three finishing files.

Shaping files #1 and #2 have tip diameters of0.185mm and 0.2mm, respectively, 14mm long cuttingblades, and partially active tips. The diameters of thesefiles at D14 are 1.2 and 1.1 mm, respectively. The finish-ing files (F1, F2, and F3) have tip diameters of 0.2, 0.25,and 0.3 mm, respectively, between D0 and D3, and thetapers are 0.07, 0.08, and 0.09, respectively. The finish-ing files have noncutting tips.

The convex triangular cross section of ProTaperinstruments reduces the contact areas between the file G

2mm

A B

C

Fig. 9-25 Design features of a GT-file. A, Lateral view. (SEM, ¥50.) B, Cross section. (SEM, ¥200.) C, Lateral view. D, Design specifications.


Size 20 GTrotary files: 4



GT accessoryfiles: 4

Tip sizes

20

30

40

35, 50,70, 90

Sizeincrements

None, tapersof .04 to .10



Varies,taper .12

r.p.m.(recommended)

150 to 350,minimal axialforce,low torque tofracture buthigher workingtorque

Lengths

18, 21,25 mm

D

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G

2mm

A B

C


12

Tip sizes

20, 25,30 with.02, .04,and .06taper; 35to 45 with.02 taper

Sizeincrements

5

r.p.m.(recommended)

300-600, withminimal axialforce

Lengths

21,25 mm

DFig. 9-26 Design features of a HERO instrument. A, Lateral view. (SEM, ¥50.) B, Cross section. (SEM, ¥200.) C, Lateral view. D, Designspecifications.

2mm

A B

C


6 (3 shapingfiles; SX, S1,S2; 3 finishingfiles; F1, F2,F3)

Tip sizes

19-30

Sizeincrements

Vary alongthe workingpart of anindividualinstrument

r.p.m.(recommended)

150 to 350minimal axialforce, low tomedium torqueto fracture,varying workingtorque

Lengths

19, 21,25 mm

DFig. 9-27 Design features of a ProTaper instrument. A, Lateral view. (SEM, ¥50.) B, Cross section. (SEM, ¥200.) C, Lateral view. D, Designspecifications.

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and the dentin. The greater cutting efficiency inherentin this design has been safely improved by balancing thepitch and helix angle, preventing the instruments frominadvertently screwing into the canal. The instrumentsare coded by colored rings on the handles. ProTaperinstruments can be used in gear reduction electricalhandpieces at 300 rpm in accordance with universallyrecognized guidelines.

In a study using plastic blocks, the ProTaper createdacceptable shapes quicker than GT rotary, ProFile, andQuantec instruments331 but also created somewhat more aberrations. In a comparison of ProTaper and K3instruments (SybronEndo, Glendora, CA), Bergmans et al30 found few differences, with the exception of sometransportation by the ProTaper into the furcationregion. A study using µCT showed that the ProTapercreated consistent shapes in constricted canals withoutobvious preparation errors, although wide canals maybe insufficiently prepared with this system.205

K3 In a sequence of constant development by their inven-tor, Dr. McSpadden, the Quantec 2000 files were fol-lowed by the Quantec SC, the Quantec LX, and thecurrent K3 system (all by SybronEndo). The overalldesign of the K3 is similar to that of the ProFile and theHERO in that it includes size #.02, #.04, and #.06instruments. The most obvious difference between theQuantec and K3 models is the K3’s unique cross-sec-tional design (Fig. 9-28): a slightly positive rake angle

for greater cutting efficiency, wide radial lands, and aperipheral blade relief for reduced friction. Unlike theQuantec, a two-flute file, the K3 features a third radialland to help prevent screwing in.

In the lateral aspect the K3 has a variable pitch andvariable core diameter, which provide apical strength.This complicated design is relatively difficult to manu-facture, resulting in some metal flash (see Fig. 9-28).

Like most other instruments the K3 features a roundsafety tip, but the file is about 4mm shorter than otherfiles (although it has the same length of cutting flutes)because of the Axxess handle. The instruments are codedby ring color and number.

Research with the K3 is limited because of its recentintroduction, but thus far its shaping ability seems to besimilar to that of the ProTaper30 and superior to thatachieved with hand instruments.238

FlexMaster The FlexMaster file system currently is not available inthe United States. It also features #.02, #.04, and #.06tapers. The cross sections (Fig. 9-29) have a triangularshape with sharp cutting edges and no radial lands. Thismakes for a relatively solid instrument core and excel-lent cutting ability. The overall manufacturing quality ishigh, with minimal metal flash and rollover.

FlexMaster files have round, passive tips; the tipdiameters are 0.15 to 0.7mm for size #.02 instrumentsand 0.15 to 0.4mm for size #.04 and #.06 files (see Fig.9-29). In addition to the standard set, the Intro file,

G

2mm

A B

C


27

Tip sizes

15-45 with.02 taper;15-60 with.04 and.06 taper

Sizeincrements

5

r.p.m.(recommended)

300 to 350,minimal axialforce

Lengths

21, 25,30 mm

DFig. 9-28 Design features of a K3 instrument. A, Lateral view. (SEM, ¥50.) B, Cross section. (SEM, ¥200.) C, Lateral view. D, Design specifications.

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G

2mm

A B

C


22

Tip sizes

15-70(.02)15-40(.04 and.06)

Sizeincrements

5; tapers of.02, .04, or.06

r.p.m.(recommended)

280 (150 to 300),Minimal axialforce, lowworking torque

Lengths

21, 25,28 mm(.02 and.04 only)

DFig. 9-29 Design features of a FlexMaster instrument. A, Lateral view. (SEM, ¥50.) B, Cross section. (SEM, ¥200.) C, Lateral view. D, Designspecifications.

which has a #.11 taper and a 9mm cutting part, is avail-able. The instruments are marked with milled rings onthe instrument shaft; the manufacturer provides asystem box that indicates sequences for narrow,medium-size, and wide canals.

Recent studies indicate that the FlexMaster allowscentered preparations in both constricted and widercanals126 and that it performed on par with othersystems.127,312 Clinical studies confirmed that the FlexMaster showed superior shaping characteristicscompared with K-files.239 Novice dental students wereable to shape plastic blocks successfully with the FlexMaster after a short training period.266,267

RaCe The RaCe was manufactured since 1999 by FKG and waslater distributed in the United States by Brasseler(Savannah, GA). The name, which stands for reamer withalternating cutting edges, describes just one design featureof this instrument (Fig. 9-30). Light microscopicimaging of the file shows twisted areas (a feature of con-ventional files) alternating with straight areas; thisdesign reduces the tendency to screw into the root canal.Cross sections are triangular or square for #.02 instru-ments with size #15 and #20 tips. The lengths of cuttingparts vary from 9 to 16mm (see Fig. 9-30).

The surface quality of the RaCe has been improvedby electropolishing, and the two largest files (size #35,#.08 taper and size #40, #.10 taper) are also available instainless steel. The tips are round and noncutting, andthe instruments are marked by color-coded handles andmilled rings.

Only recently have the results of in vitro experimentscomparing RaCe to other contemporary rotary systemsbecome available.240,241 Canals in plastic blocks and inextracted teeth were prepared by the RaCe with lesstransportation from the original curvature thanoccurred with the ProTaper.240

The preceding descriptions covered only a limitedselection, the most popular and widely used rotaryinstruments on the market. New files, such as theSequence by Real World Endo (distributed by Brasselerbut manufactured by FKG), are continually added to thearmamentarium, and older systems are updated. Thus itis next to impossible to keep track of file designs.

To summarize, most systems include files with tapersgreater than the #.02 stipulated by the ISO norm. TheLightSpeed is different from all other systems, the Pro-Taper and RaCe have some unique features, and mostother systems have increased tapers. Minor differencesexist in tip designs, cross sections, and manufacturingprocesses, but the clinical effects of these modificationscurrently are unknown. Even in vitro, tests have onlybegun to identify the effect of specific designs onshaping capabilities31,198 and clinical outcomes.200,239

Equally little is known about the physical parametersgoverning rotary root canal preparation. However, thesefactors are crucial, because NiTi rotary files have anincreased risk of fracture compared with K-files. In astudy using plastic blocks, as many as 52 ProFile Series29 instruments became permanently deformed.285 Threefractures were reported in a subsequent study on ISO-norm ProFile size #.04 instruments, and three otherinstruments were distorted.46 An even higher fracture

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incidence was shown in a study on rotary instrumentsused in plastic blocks in a specially designed testingmachine.280 These findings were confirmed by twostudies in which high fracture incidences were reportedfor LightSpeed and Quantec rotary instruments used ina clinical setting.18,231 Consequently, a benefit versus riskanalysis must be done for all rotary NiTi instruments,addressing the reasons and the clinical consequences ofinstrument fracture.

Physical and Chemical Properties of NiTi Alloys During the development of the equiatomic nitinol alloy(55% [by weight] nickel and 45% [by weight] titanium),a shape memory effect was noted; this was attributed tospecific thermodynamic properties of the new alloy.48

The alloy sparked interest in dental research because ofits “shape recovery” property after passage through crit-ical temperatures.63 Some researchers envisioned themanufacture of nondulling rotary instruments from analloy called 60-nitinol. However, nickel-titanium wirewas found to be difficult to bend into clamp retainers.63

Subsequently, researchers thought that the superelas-tic properties of 55-nitinol might prove advantageous inendodontics, and the first hand instruments producedfrom 55-nitinol were tested (Fig. 9-31).302 That studyfound that size #15 NiTi instruments were two to threetimes more flexible than stainless steel instruments.Nickel-titanium instruments showed superior resistanceto angular deflection; they fractured after 21/2 full revo-

lutions (900 degrees) compared with 540 degrees forstainless steel instruments (Fig. 9-31, C).

Furthermore, hardly any plastic deformation ofcutting flutes was recorded when an instrument wasbent up to 90 degrees,302 and forces required to bendendodontic files to 45 degrees were reduced by 50%with nickel-titanium.250 In the latter study, the authorsspeculated that heat, probably during sterilizationcycles, could even restore the molecular structure ofused NiTi files, resulting in an increased resistance tofracture.

Specific properties of nickel-titanium can beexplained by specific crystal structures of the austeniteand martensite phases of the alloy.281 Heating the metalabove 212∞ F (100∞ C) may lead to a phase transition,and the shape memory property forces the instrumentback to a preexisting form. Likewise, linear deformingforces are shunted into a stepwise transition from anaustenitic to a martensitic lattice, and this behaviorleads to a recoverable elastic response of up to 7% (Fig. 9-31, A).

However, graphs such as those shown in Fig. 9-31, B,are generated when larger NiTi instruments are sub-jected to angular deflection until failure. Such graphsshow different results for stainless steel instruments,which produce a relatively steep stress-strain curve withless than 1.3% recoverable deformation.281 As stated pre-viously, the superelastic behavior of nickel-titanium alsodictates the production of NiTi instruments, which must G

2mm

A B

C


15

Tip sizes

15-60(.02)

25-35(.04)30, 40(.06)35 (.08)40 (.10)

Sizeincrements

5 and 10

Varyingtapers

r.p.m.(recommended)

Up to 600,

Minimal axialforce

Lengths

19,

25 mm

DFig. 9-30 Design features of a RaCe instrument. A, Lateral view. (SEM, ¥50.) B, Cross section. (SEM, ¥200.) C, Lateral view. D, Design specifications.

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be milled or ground (stainless steel blanks can simplybe twisted to produce K-files or reamers). Consequently,NiTi instruments may have characteristic imperfectionssuch as milling marks, metal flashes, orrollover.83,250,293,302 Some researchers even speculate thatfractures in nickel-titanium instruments originate atsuch surface imperfections.11,160 Other studies have sug-gested that chloride corrosion may lead to micropit-ting230 and subsequent fracture in NiTi instruments.117

However, only immersion in disinfecting solution for extended periods (e.g., overnight) produced corro-sion of NiTi instruments and subsequent decreased torsional resistance.186 Regular cleaning and sterilizationprocedures do not seem to affect NiTi rotary instruments.157,175,275

In one study, only limited material loss occurredwhen NiTi LightSpeed instruments were immersed in1% and 5% NaOCl for 30 to 60 minutes.49 Corrosionof NiTi instruments used in the clinical setting, there-fore, might not significantly contribute to fractureexcept when the instruments are immersed in heatedNaOCl for longer than 60 minutes.

In general, instruments used in rotary motion breakin two distinct modes, torsional and flexural.199,231,299

Torsional fracture occurs when an instrument tip islocked in a canal while the shank continues to rotate,thereby exerting enough torque to fracture the tip. Thisalso may occur when instrument rotation is sufficientlyslowed in relation to the cross-sectional diameter. Incontrast, flexural fracture occurs when the cyclic loadleads to metal fatigue. This problem precludes the manufacture of continuously rotating stainless steelendodontic instruments, because steel develops fatalfatigue after only a few cycles.250 NiTi instruments canwithstand several hundred flexural cycles before theyfracture.116,154,214,327

Repeated loading and cyclic fatigue tests forendodontic instruments are not described in pertinentnorms. Initially, rotary instruments such as Gates-Glidden burs and Peeso reamers were tested with asuperimposed bending deflection.40 In Gates-Gliddenburs, a 2mm deflection of the instrument tip resultedin fatigue life spans ranging from 21,000 revolutions(size #1 burs) to 400 revolutions (size #6 burs).40 Inanother study, stainless steel and nickel-titanium handfiles were rotated to failure in steel tubes with an acute90-degree bend and an unspecified radius.250 Underthese conditions, size #40 stainless steel instrumentsfractured after fewer than 20 rotations, whereas variousnickel-titanium files of the same size withstood up to450 rotations.

Cyclic fatigue was also evaluated for ProFile size #.06instruments using a similar device.326,327 The number ofrotations to failure for unused control instrumentsranged from 1260 (size #15 files) to 900 (size #40 files). These scores did not change when the instrumentswere tested under simulated clinical conditions, such as repeated sterilization and contact with 2.5% sodium hypochlorite. Subsequently, control instru-ments were compared with a group of instruments usedin the clinical setting in five molar cases326; again, nosignificant differences were found in resistance to cyclicfatigue.

Haikel et al116 used a different testing method involv-ing tempered metal cylinders with radii of 5mm and10mm that produced a 90-degree curve. They reportedfatigue fractures for size #15, #.04 taper ProFile instru-ments after about 2800 cycles with the 10mm cylinders;in size #40, #.04 taper ProFile instruments, fracturesoccurred after about 500 cycles with the 5mm cylinders.In comparison, size #15, #.06 taper ProFile instrumentsfailed also after about 2800 revolutions with the 10mmG

1500

1000

500

0

10

20

30

00

0 80 160 240 320 400 480

E

5

Linear strain [%]

Str

ess

[MP

a]S

tres

s [M

Pa]

Torsional strain [∞]

Hookian elasticity (stainless steel)

SETransformational elasticity (NiTi)

10

A

B

CFig. 9-31 Stress-strain behavior of nickel-titanium alloy. A,Schematic diagram of linear extension of a NiTi wire. B, Torque tofailure test of a size #60, #.04 taper ProFile NiTi instrument. Notethe biphasic deformation, indicated by arrows in A and B. C, Com-parison of stainless steel and nickel-titanium crystal lattices underload. Hookian elasticity accounts for the elastic behavior (E) of steel,whereas transformation from martensite to austenite and backoccurs during the superelastic (SE) behavior of NiTi alloy. (C modi-fied from Thompson S: Int Endodon J 33:297-310, 2000.)

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cylinders, but failure occurred in size #40, #.06 taperProFile specimens after only 223 cycles with the 5mmcylinders.

Rotary nickel-titanium instruments with larger tapersand sizes consistently fractured after fewer rotations,and although the radius of the curves was halved,fatigue-life was reduced by 400%. Haikel et al116

reported similar results for selected HERO instruments,and their findings were confirmed by other tests on GTrotary instruments. Size #20, #.06 taper GT files failedafter 530 rotations in a 90-degree curve with a 5mmradius; size #20, #.12 taper GT files failed after 56 rotations under the same conditions.202

Norms, specifications, tolerances, and other physicalparameters have been described for stainless steel handinstruments such as K-files and Hedström files.131

However, no comparable norms exist for instrumentsused in continuous rotary motion. Consequently, anumber of models have been devised to assess specificproperties of nickel-titanium rotary instruments, includ-ing torque at failure, resistance against cyclic fatigue,and others (Fig. 9-32). These systems can assess simul-taneously torque at failure, working torque axial force,and cyclic fatigue (Fig. 9-33).

According to the norms mentioned previously,torque at failure is recorded with the apical 3mm of theinstrument firmly held in the testing device while theinstrument’s’ handle is rotated. A wide variety of rotarynickel-titanium endodontic instruments have beentested in this way. For example, ProFile NiTi rotary filesin ISO sizes #25, #30, and #35 (#.04 taper) fractured at0.78, 1.06, and 1.47 Ncm, respectively.275

Svec and Powers276 reported similar scores wheninstruments were forced to fracture in plastic blockswith simulated curved canals. In a different setup, GTrotary instruments (size #20, #.06 taper to size #20, #.12

taper) fractured at 0.51 and 1.2 Ncm, respectively.202 Theresults of other studies describing torque at failure loadsare in general agreement with these findings.*

Compared with NiTi instruments with tapered flutes,LightSpeed instruments had lower torques to fracture(0.23 to 2 Ncm171).

When analyzing clinical factors involved in instru-ment fracture, one must consider both torsional loadand cyclic fatigue231 (Fig. 9-34). However, these are notseparate entities, especially in curved canals38; workingan instrument with high torque may lower resistance tocyclic fatigue.94 Conversely, cyclic prestressing has beenshown to reduce the torsional resistance of ProTaper fin-ishing files.299 Also, cyclic fatigue occurs not only in thelateral aspect, when an instrument rotates in a curvedcanal, but also axially, when an instrument is boundand released by canal irregularities.33

The torque generated during canal preparationdepends on a variety of factors, and an important oneis the contact area.36 The size of the surface area con-tacted by an endodontic instrument is influenced by theinstrumentation sequence or by the use of instrumentswith different tapers.244 A crown-down approach is rec-ommended to reduce torsional loads (and thus the riskof fracture) by preventing a large portion of the taperedrotating instrument from engaging root dentin (knownas taper lock).36,328

The clinician can further modify torque by varyingaxial pressure, because these two factors are related244

(see Fig. 9-33). In fact, a light touch is recommendedfor all current NiTi instruments to avoid forcing theinstrument into taper lock. The same effect might occurin certain anatomic situations, such as when canalsmerge, dilacerate, and divide.

The torsional behavior of nickel-titanium rotaryendodontic instruments cannot be described properlywithout advanced measurement systems and a new setof norms. However, the clinician must be able to inter-pret correctly the stress-strain curves for all rotary nickel-titanium instruments used in the clinical setting to beable to choose an appropriate working torque and axialforce.

Motors and Devices

Newer motors have been developed for rotary instru-ments since the simple electric motors of the first gen-eration in the early 1990s (Fig. 9-35, A). Electric motorswith gear reduction are more suitable for rotary NiTisystems because they ensure a constant rpm level;however, they also deliver torques much higher thanthose required to break tips. Some authors believe thattorque-controlled motors (Fig. 9-35, B to D), whichhave been used for several years, increase operational

G

A

BC

D

Fig. 9-32 Testing platform for analysis of various factors duringsimulated canal preparation with rotary endodontic instruments.Labeled components are a force transducer (A), a torque sensor (B),a direct-drive motor (C), and an automated feed device (D). For spe-cific tests, a cyclic fatigue phantom or a brass mount compliant withISO no. 3630-1 (inserts) may be attached.

*References 37, 144, 224, 231, 322, and 323.

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safety.95 However, others have suggested that torque-control motors may be helpful mainly to inexperiencedclinicians.328 These motors probably do not reduce therisk of fracture caused by cyclic fatigue; also, even if thetorque is below the fracture load at D3, a fracture at thesmaller diameter (D2) is still possible.

To complicate matters further, an obvious differentialexists between torque at failure at D3 and the workingtorque needed to operate an instrument effectively (Fig.9-36 and Box 9-2).37,125,199,204,232 In many cases theworking torque is greater than the torque required tofracture the instrument’s tip. However, the tip will notbreak if a passive glide path has been verified.

This differential is especially large with files with ataper greater than #.06; therefore, these files are ratherineffective in most torque-controlled motors. Mostmotors allow adjustment of torque for the instrumentused, either with a key or a system card that is insertedinto the box.

Other factors that may influence the incidence offracture in motor-driven NiTi rotary instruments arelubrication, specific instrument motion, and speed ofrotation. It cannot be overemphasized that nickel-titanium rotary instruments should be used only incanals that have been flooded with irrigant. Althoughlubricants such as RC-Prep (Premier, Norristown, PA)and Glyde (Dentsply Maillefer) have also been recom-

mended, their benefit has not been proved conclu-sively.201 In fact, because of chemical interactionsbetween NaOCl and ethylenediamine tetra-acetic acid(EDTA), alternating irrigants and using lubricants thatcontain EDTA may even be counterproductive. More-over, no data have been produced linking the use oflubricants to reduction of torque during root canalpreparation.

For instrument motion, most manufacturers recom-mend a pecking, up and down motion. This not onlyprevents screwing in of the file, it also distributes stressesaway from the instrument’s point of maximum flexure,where fatigue failure would likely occur.154,214 Oscillat-ing movements did not significantly enhance the lifespan of ProFile size #.04 or GT rotary instrumentsrotated around a 5mm radius cylinder with a 90-degreeG

1.5

1.0

0.5

0

0 2

Torq

ue [N

cm]

For

ce [N

]D

ista

nce

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]

4 6 8 10 12

8

6

4

20

10

0

0

2

0 2 4 6 8 10 12

0

Time [s]

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A

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ue [N

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ce [N

]D

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[mm

]

4 6 8 10 12

8

6

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20

10

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0

2

0 2 4 6 8 10 12

0

Time [s]

2 4 6 8 10 12

BFig. 9-33 Physical factors (torque, axial force, and insertion depth) that affect root canal instrumentation documented with a torque-testingplatform. A, ProFile size #45, #.04 taper used in a mildly curved canal of a single-rooted tooth, step-back after apical preparation to size #40.B, FlexMaster size #35, #.06 taper used in a curved distobuccal canal of a maxillary first molar, crown-down during the initial phase of canalpreparation.

Box 9-2 Instrument Breakage withTorsional Load (MacSpaddenFactor)

For rotary instrument tips, susceptibility to breakage is gov-erned by the quotient of torque needed to fracture dividedby working torque. Simply put, the larger the value, the saferthe file.

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G

A B

DCFig. 9-34 Scanning electron micrographs of deformed or separated nickel-titanium rotary instruments. A, Lateral view of a ProTaper F3instrument after application of torsional load. (¥25.) B, Lateral view of a size #35, #.04 taper FlexMaster instrument after more than 500 rota-tions in a 90-degree curve with a 5 mm radius (see Fig. 9-31). (¥30.) C, Cross section of the ProTaper instrument in A. Note signs of ductilefracture near center of the instrument core. (¥140.) D, Cross section of FlexMaster instrument in B. (¥100.)

A B

C DFig. 9-35 Examples of motors used with rotary nickel-titanium endodontic instruments. A, First-generation motor without torque control.B, Fully electronically controlled second-generation motor with sensitive torque limiter. C, Frequently used simple torque-controlled motor. D, Newest-generation motor with built-in apex locator and torque control.

curve.199,202 Furthermore, large variations were noted in the lengths of the fractured segments,125,299 which suggests that ductile fractures may originate at points of surface imperfections.

Rotational speed may also influence instrumentdeformation and fracture. Some studies indicated that

ProFile instruments with ISO-norm tip diameters failedmore often at higher rotational speed,79,93 whereas otherstudies did not find speed to be a factor.76,137

Clinicians must fully understand the factors thatcontrol the forces exerted on continuously rotating NiTiinstruments (Box 9-3). To minimize the risk of fracture

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and prevent taper lock, they should not try to forcemotor-driven rotary instruments in an apical direction.Similarly, acute apical curves limit the use of instru-ments with higher tapers because of the risk of cyclicfatigue. The incidence of instrument fracture can bereduced to an absolute minimum if clinicians use datafrom well-designed torque and stress studies. Adequateprocedural strategies, a detailed knowledge of anatomicstructures, and specific instrumentation sequences mayalso improve shaping results.

Specific procedures have been developed for remov-ing fractured instruments from root canals (Fig. 9-37);these are discussed in detail elsewhere in this book (seeChapter 25). Most of those methods require the use ofadditional equipment, such as a dental operating micro-scope and ultrasonic units. However, the best way todeal with instrument fracture is prevention. An under-standing of the anatomy of the root canal system,

together with a clear plan for selecting, sequencing, andusing shaping instruments, can certainly help preventprocedural mishaps.

Disinfectants, Dentin Surface Modifiers, and Lubricants

Studies have demonstrated conclusively that mechani-cal instrumentation cannot sufficiently disinfect rootcanals, regardless of whether stainless steel52 or nickel-titanium75 instruments are used (Fig. 9-38). Irrigationsolutions are required to eradicate microorganisms, andover time a variety of chemicals have been promoted forthis purpose. The ideal irrigant or combination of irrig-ants kills bacteria, dissolves necrotic tissue, lubricatesthe canal, removes the smear layer, and does not irritatehealthy tissues.103,129 Some formaldehyde-containingmaterials are no longer recommended for clinical use,but many irrigating solutions and varying concentra-tions of commonly used materials are described in theliterature. Some solutions used in the past were sterilesaline, NaOCl, and detergents (e.g., quaternary ammo-nium compounds, chlorhexidine, citric acids, andEDTA).271 This section describes current materials andgives some recommendations for their clinical use.

Sodium Hypochlorite A 0.5% solution of sodium hypochlorite was used effec-tively during World War I to clean contaminatedwounds.74 Also, NaOCl at varying concentrations hasbeen in use in root canal therapy for many decades.303

NaOCl is effective against endodontic microorganisms(Table 9-1), including those difficult to eradicate fromG

K-Files 15-45, Iso 3630-1 (1992)

0 10

Fra

ctur

e lo

ad a

t D3

Wor

king

torq

ue

20 30

Torque [Nmm]

40 50

NiTi K-Files 15-45, Rowan (1996)

Quantec 15-45, Sattapan (2000)

GT 20/.06-/.12, Peters (2001)

ProFile 20/.04 60/.04, Peters (2002)

Quantec, Sattapan (2000)

GT 20/.06-/.12, Peters (2001)

ProFile 20/.04-35/.06, Blum (1999)

ProFile 20/.04-60/.04, Peters (2002)

ProTaper S1-F3, Peters (2003)

ProTaper SX-F3, Blum (2003)

Flexmaster 15-45, Hübscher (2003)

Fig. 9-36 Diagram comparing fracture loads at D3 (upper section of graph) to torques occurring during preparation of root canals (lowersection of graph). Filled columns represent the largest file in each set, and open columns show the scores of the most fragile file (see textand Box 9-3 for details).*

Box 9-3 Factors Governing the Potentialfor Nickel-Titanium RotaryInstrument Fractures

• Clinician’s handling (most important)• Combination of torsional load, bending, and axial fatigue• Root canal anatomy• Manufacturing quality

*References 36, 37, 125, 131, 199, 201, 203, 224, and 231.

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root canals, such as Enterococcus, Actinomyces, andCandida organisms.*

In root canal treatment, NaOCl solutions are used atconcentrations ranging from 0.5% to 5.25%. In infecteddentin blocks, a 0.25% solution of NaOCl was sufficientto kill Enterococcus faecalis in 15 minutes; a concentra-tion of 1% NaOCl required 1 hour to kill Candida albi-cans.247 NaOCl dissolves organic material, such as pulptissue and collagen. Lower concentrations (e.g., 0.5% or1%) dissolve mainly necrotic tissue.332 Higher concen-trations allow better tissue dissolution but dissolve both

necrotic and vital tissue, which is not always a desirableeffect. In some cases full-strength NaOCl (5.25%) maybe indicated; however, although higher concentrationsmay increase antibacterial effects in vitro,329 enhancedclinical effectiveness has not been demonstrated con-clusively for concentrations stronger than 1%.

Commercially available household bleach contains5.25% NaOCl, has an alkaline pH of 12 to 13, and ishypertonic.271,332 Some authors recommend dilution ofcommercially available NaOCl with 1% bicarbonateinstead of water to adjust the pH to a lower level.74,271

Others do not see any reduction of the aggressivenesson fresh tissue by buffering NaOCl and recommend G*References 29, 114, 115, 118, 182, 195, and 307.

A B

C D

E FFig. 9-37 Removal of a separated NiTi instrument from a mesiolingual canal of a mandibular molar. A, Fragment located in the middlethird of the root. B, Clinical aspect of the fragment after enlargement of the coronal third of the root canal with modified Gates-Glidden drills,visualized with an operating microscope. (¥25.) C, Radiograph taken after removal of the fragment; four hand files have been inserted intothe canals. D, Final radiograph shows slight widening of the coronal third of the mesiolingual canal and fully sealed canal systems. A fullcrown was placed immediately after obturation. E, Recall radiograph 5 years after obturation shows sound periradicular tissues. F, Removedfragment and separated file (gradation of ruler is 0.5 mm).

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G

Table 9-1 Activity of Various Irrigants against Microorganisms*

NAOCL

Enterococci3 min at 0.0005%

solution in filterpaper specimens

15 min at 0.25% solu-tion in contaminateddentin blocks331

30 min at 0.5% solu-tion and 2 min at5.25% solution indirect contact withbacteria214

1 min at 1% solution20

10 sec at 0.5% solu-tion in direct contactwith bacteria214

1 hour at 1% or 5%solution on rootdentin with smearlayer246

30 sec for both the0.5% solutions tokill all cells inculture305

CHX

7 days of 0.5% dress-ing resulted in com-plete killing in dentinblocks up to fulldepth of 950 mm259

24 hours to reducecultured bacteriabelow detectionlimit211

No growth directlyafter rinsing with 2%CHX in patients withnecrotic pulpsand/or apical granu-loma85

3 days for 2% CHX toeliminateActinomyces israeliifrom all samples ofinfected dentin23

1 hour at 0.12% solu-tion on root dentinwith smear layer246

10 sec at 0.5% solu-tion in direct contactwith bacteria214

5 min at 0.5% solu-tion to kill all yeastcells and 1 hour at0.05% solution; lesseffective than IKIand NaOCl305

?

IKI

24 hours of iodine(2%) exposure inpotassium iodide(4%) resulted incomplete killing indentin blocks up toa depth of700 mm259

1 hour to reduce bac-teria under 0.1%and 24 hours toreduce bacteriabelow detectionlimit; however, lossof activity notedthrough dentinpowder211

30 sec for both 2%and 4% solutions tokill all cells inculture; 0.2% and0.4% solutions wereas effective as 0.5%CHX305

MTAD

5 min applicationresulted in nogrowth on infecteddentin251

MTAD was as efficientas 5.25% NaOCl incultures290

CA(OH)2

24 hours to reducecultured bacteriabelow detectionlimit, but activity wasinhibited by dentinpowder, hydroxyap-atite, and serumalbumin211

7 days to rendercanals bacteria free50

but showed littleeffect on Enterococ-cus faecalis50;resulted in completekilling in dentinblocks up to fulldepth of 950 mm259

7 days of Ca(OH)2 in0.5% chlorhexidineacetate dressingresulted in completekilling in dentinblocks up to fulldepth of 950 mm259

After 1 hour and 24hours only a smallreduction of CFUwas observed305

Actinomyces Organisms

Candida Organisms

*Effects achieved by killing through antimicrobial action.NaOCl, Sodium hypochlorite; CHX, chlorhexidine acetate; IKI, iodine potassium iodide; Ca(OH)2, calcium hydroxide.

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diluting solutions of NaOCl with water to obtain lessconcentrated irrigation solutions.332

NaOCl only minimally removes dentin or smearlayer (Fig. 9-39); therefore, some recommend concur-rent use of demineralizing agents to enhance cleaningof difficult-to-reach areas, such as dentinal tubules andlateral canals.50,185

ChlorhexidineChlorhexidine (CHX) is a broad-spectrum antimicro-bial agent effective against gram-negative and gram-pos-itive bacteria (see Table 9-1). It has a cationic molecularcomponent that attaches to negatively charged cellmembrane areas, causing cell lysis. CHX has been usedin periodontal therapy for many years. Its use as anendodontic irrigant59,88,123 is based on its substantivityand long-lasting antimicrobial effect, which arises frombinding to hydroxyapatite. However, it has not beenshown to have clinical advantages over NaOCl.

Some researchers found that CHX had significantlybetter antibacterial effects than calcium hydroxideCa(OH)2 when tested on cultures.156 Effective combina-tions of CHX and Ca(OH)2 are available and show

strong antimicrobial activity against obligate anaerobes,the combination augmenting the antibacterial effect ofeither medicament on certain species.209,260 The additionof CHX or iodine potassium iodide to an intracanaldressing of Ca(OH)2 in vitro did not affect the alkalin-ity (and hence the efficacy) of the calcium hydroxidesuspensions.260

Iodine Potassium IodideIodine potassium iodide (IKI) is a traditional root canaldisinfectant. IKI kills a wide spectrum of microorgan-isms found in root canals (see Table 9-1) but shows relatively low toxicity in experiments using tissue cul-tures.270 Iodine acts as an oxidizing agent by reactingwith free sulfhydryl groups of bacterial enzymes, cleav-ing disulfide bonds. E. faecalis often is associated withtherapy-resistant periapical infections (see Chapter 15),and combinations of IKI and CHX may be able to killcalcium hydroxide–resistant bacteria more efficiently. Arecent study by Sirén et al260 evaluated the antibacterialactivity of a combination of calcium hydroxide with IKIor CHX in infected bovine dentin blocks. Althoughcalcium hydroxide alone was unable to destroy E. fae-calis inside dentinal tubules, calcium hydroxide mixedwith either IKI or CHX effectively disinfected dentin. Anobvious disadvantage of iodine is a possible allergicreaction in some patients. G

100�m

A

BFig. 9-38 Remaining potentially infected tissue in fins andisthmus configuration after preparation with rotary instruments. A,Cross section through a mesial root of a mandibular molar, middleto coronal third of the root. Both canals have been shaped; the leftone is transported mesially. (¥10.) B, Magnified view of rectanglein A. Note the presence of soft tissue in the isthmus area. (¥63.)(Courtesy Professor H. Messer.)

A

B

C

D

E

Fig. 9-39 Surface textures of an unprepared root canal at variouslevels. A, Ground section of a mandibular premolar. Areas viewedby scanning electron microscopy (SEM) are indicated by black lines.B, Canal surface at middle section, showing open dentinal tubulesand typical calcospherites. (¥500.) C to E, Coronal, middle, andapical areas as compound scanning electron micrographs. Note thenumerous open tubules in C and D, whereas fewer tubules arevisible in E. (¥200.)

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MTAD New chemicals for irrigating root canals are constantlydeveloped, including solutions based on antibiotics.Use of these irrigants is controversial, however, becauseof the emergence of increasingly resistant strains of bac-teria (e.g., therapy-resistant enterococci), which may bedue to overprescription of antibiotics in general. Theincreased risk of host sensitization by local antibioticscan be circumvented to some degree by using theantibiotic as a dressing. Because exposure to vital tissuesis limited, higher microbicidal concentrations may beused.177 A number of antibiotics, including erythromy-cin, chloramphenicol, tetracycline, and vancomycin,have been tested successfully against enterococci. In onestudy, investigators evaluated microbial susceptibility todifferent antibiotics in vitro; they found that enterococ-cal isolates were resistant to benzylpenicillin, ampi-cillin, clindamycin, metronidazole, and tetracycline butsensitive to erythromycin and vancomycin.73 MTAD(Dentsply–Tulsa), a recently introduced irrigation solution, contains doxycycline, citric acid, and a sur-face-active detergent (Tween 80).291 In vitro experimentsindicate that MTAD has potential for removing thesmear layer,26,251,289 but clinical benefits have yet to bedemonstrated.

Ethylenediamine Tetra-Acetic Acid EDTA came into use in endodontics in 1957,185 whereasNaOCl has been in use for more than 70 years.303 Chela-tors such as EDTA create a stable calcium complex withdentin mud, smear layers, or calcific deposits along thecanal walls. This may help prevent apical blockage (Fig.9-40) and aid disinfection by improving access of solu-tions through removal of the smear layer.

Neutral EDTA showed a higher degree of decalcifica-tion of dentin surfaces than RC-Prep, although its effectwas reduced in apical regions.301 Similar to MTAD, RC-Prep did not erode the surface dentin layer.289

The effect of chelators in negotiating narrow, tortu-ous, calcified canals to establish patency depends bothon canal width and on the amount of active substanceavailable as the demineralization process continuesuntil all chelators have formed complexes withcalcium.129 Calcium binding results in the release ofprotons, and EDTA loses its efficiency in an acidic envi-ronment. Thus the action of EDTA is thought to be self-limiting.246 In one study, demineralization up to a depthof 50mm into dentin was demonstrated for EDTA solu-tions129; however, reports demonstrated significanterosion after irrigation with EDTA.289

A comparison of bacterial growth inhibition showedthat the antibacterial effects of EDTA were stronger thancitric acid and 0.5% NaOCl but weaker than 2.5%NaOCl and 0.2% chlorhexidine.257 EDTA had a signifi-cantly better antimicrobial effect than saline solution; itexerts it strongest effect when used synergistically with

NaOCl, although no disinfecting effect on colonizeddentin could be demonstrated.123

Recent reports have indicated that several disinfect-ing agents such as Ca(OH)2, IKI, and CHX are inhibitedin the presence of dentin.112,211,212 Moreover, chemicalanalyses indicated that chlorine, the active agent inNaOCl, is inactivated by EDTA.107,333

In light of these facts, in addition to the unproveneffect of lubricants containing EDTA on rotary instru-ment torque, use of these solutions probably should belimited to hand instrumentation early in a procedure.Moreover, an EDTA solution preferably is used at theend of a procedure to remove the smear layer.322,333 Thisand/or sufficient volume of NaOCl ensures high disin-fecting efficacy by enabling NaOCl to penetrate eveninto deeper dentin layers (Fig. 9-41).

Calcium Hydroxide Ca(OH)2 is very effective at eradicating intraradicularbacteria. Unfortunately, it is not as effective when usedshort term262; therefore, it requires prolonged exposure19

or higher temperatures for use as an endodontic irrigant.88

Other Irrigants Electrochemically activated water (also known as oxidative potential water) recently was tested as a potentialirrigant.110,169,265 Although this solution is active againstbacteria110 and removes the smear layer,169 no evaluationsof its clinical potential are available, and in vitro researchindicates that NaOCl is a superior disinfectant.110

Hydrogen peroxide traditionally has been used as anirrigant in conjunction with NaOCl; however, no addi-tional benefit to NaOCl was registered.123G

A

B

Fig. 9-40 Presence of dentin dust as a possible source of micro-bial irritation. Tooth #18 underwent root canal therapy. The cliniciannoted an apical blockage but was unable to bypass it. Unfortu-nately, intense pain persisted and at the patient’s request, the toothwas extracted a week later. A, Mesial root of tooth #18; mesialdentin has been removed. B, Magnified view (¥125) of rectangle inA shows an apical block (gradation of ruler is 0.5 mm).

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Recently some have advocated the use of 0.2% or0.5% CHX mixed in addition to sodium hypochlo-rite,112,123 either as an irrigant or mixed with Ca(OH)2 asan interappointment medicament. These combinationscan overcome the inhibiting effect of dentin dust onconventional medicaments112,212 and can optimize theirantimicrobial properties against certain resistant bacteria and yeasts.306,309 Increased effectiveness wasobserved when Ca(OH)2 was mixed with somecommon irrigating solutions. Although some authorscould not confirm additive effects and even found areduction in the antimicrobial action of CHX,119 itappears that Ca(OH)2 mixed with IKI or CHX may beable to kill calcium hydroxide–resistant bacteria260

(Box 9-4).

Lubricants In root canal treatment, lubricants are mostly used toemulsify and keep in suspension debris produced bymechanical instrumentation. Although irrigation solu-tions serve as lubricants, special gel-type substances arealso marketed. Two of these are the wax-based RC-Prep,which contains EDTA and urea peroxide, and the glycol-based Glyde. Another purported function of lubricantsis to facilitate the mechanical action of endodontichand or rotary files. A study evaluating the effects oflubrication on cutting efficiency found that tap waterand 2.5% sodium hypochlorite solutions increasedcutting efficiency compared with dry conditions.330 Theauthors of this study cited the ability of a lubricant toremove debris as the factor for the increased efficiency.Similarly, in recent experiments a reduction of torquescores was found when canals in normed dentin diskswere prepared with ProFile and ProTaper instrumentsunder irrigation; use of a gel-type lubricant resulted insimilar torques).201

In summary, irrigation is an indispensable step inroot canal treatment to ensure disinfection. The tissue-dissolving and disinfecting properties of NaOCl cur-rently make it the irrigant of choice. EDTA should beused at the end of a procedure to remove the smearlayer, followed by another flush with NaOCl or an inertsolution such as physiologic saline. This minimizesinactivation of NaOCl by chemical interactions.

CLEANING AND SHAPING: CLINICAL ISSUES

Endodontists widely agree that a major biologic aim ofendodontic therapy is to eliminate apical periodontitisby disinfection and sealing of root canal systems.However, considerable disagreement exists over the waythis goal should be achieved (see Fig. 9-9). Although“cleaning and shaping” accurately describes themechanical procedures,227 it should be emphasized that“shaping and cleaning” more correctly reflects the factthat enlarged canals direct and facilitate the cleaningaction of irrigants and the removal of infected dentin. G

17% EDTAH2O

Coronal 1/3

Middle 1/3

Apical 1/3

Fig. 9-41 Penetration of irrigants into dentinal tubules after root canal preparation with different dentin pretreatments. Leftcolumn, Irrigation with tap water and then with blue dye. Rightcolumn, Smear layer is removed with 17% EDTA, applied in highvolume and with a 30-gauge needle, followed by irrigation with bluedye. Note the comparable diffusion of dye in the apical sections,whereas dye penetrated deeper into the dentin in the two coronalsections.

Box 9-4 Benefits of Using Irrigants inRoot Canal Treatment

• Removal of particulate debris and wetting of the canalwalls

• Destruction of microorganisms• Dissolution of organic debris• Opening of dentinal tubules by removal of the smear

layer• Disinfection and cleaning of areas inaccessible to

endodontic instruments

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Microorganisms in the pulp cavity and coronal rootcanal may be readily killed by irrigants early in a pro-cedure; however, bacteria in less accessible canal areasstill can elicit apical periodontitis. These bacteria can beeradicated only after root canal preparation.

Biologic Objectives

Some have suggested that canals should be prepared toa uniform and continuous taper242; however, thismechanical objective facilitates obturation rather thanantimicrobial efficacy. The preparation shape andantimicrobial efficacy are intimately related through theremoval of infected dentin and the delivery of irrigants.

Traditionally fluids have been delivered to root canalspassively by syringe and needle (Fig. 9-42); activesystems such as the NIT are still in an experimentalphase.166 When delivered passively, irrigants have beenshown to progress only 1mm farther than the tip of theneedle.216 However, enlarged apical canals are likely toallow increasingly deeper needle placement (see Fig. 9-42), and this improves debridement and disinfection ofcanals.6 Nevertheless, thorough cleaning of the mostapical part of any preparation remains difficult,318

especially in narrow and curved canals.122,192,219

Mechanical Objectives

An important mechanical objective of root canal instru-mentation is full incorporation of the original canalsinto the prepared shape, meaning that all root canal sur-faces are mechanically prepared (green areas in Fig. 9-43, A and B); however, this goal is not possible withcurrent techniques.203

Preparation errors, such as zips and perforations,should be absent. Although these and other proceduralproblems (Fig. 9-44) per se may not affect the proba-bility of a favorable outcome, they may leave parts ofthe root canal system inaccessible for disinfection.

Another important mechanical objective is to leaveas much radicular dentin as possible so as not to weakenthe root structure, thereby preventing vertical fractures.Although no definitive minimal radicular thickness hasbeen established, 0.2mm is considered critical.155 Strai-ghtening of canal paths can lead to minimal remainingwall thicknesses (Fig. 9-45); this underlines the need foradequate access cavity preparation and optimal enlarge-ment of the coronal third of the root canal.

Two primary mechanical elements are the apicalwidth and the endpoint of the prepared shape in rela-tion to the apical anatomy. Traditional treatment hasheld that canal preparation and subsequent obturationshould terminate at the apical constriction, the narrowestdiameter of the canal. This point is believed to coincidewith the cementodentinal junction (CDJ) (see Chapter7). This definition of working length is based on histo-logic sections and ground specimens. However, the

position and anatomy of the CDJ varies considerablyfrom tooth to tooth, from root to root, and from wallto wall in each canal. Moreover, the CDJ cannot belocated precisely on radiographs. For this reason, somehave advocated terminating the preparation 0.5 to 1mmshort of the radiographic apex in necrotic cases and 1 to2mm short120,222,321 in cases involving irreversible pulpi-tis. In this way, preparation would take place inside theroot canal. Follow-up studies seem to support this strategy.261,263

However, working to shorter lengths could lead to theaccumulation and retention of debris, which may resultin apical blockage (see Fig. 9-40). Such blockage (whichconsists of collagen fibers, dentin mud, and residualbacteria) inside apical canal areas is a major cause ofpersistent or recurrent apical periodontitis,115,256 recentlylabeled posttreatment disease92 (also see Chapter 24).Moreover, because of the creation of apical blockage,working to short lengths may contribute to proceduralerrors such as apical perforations and fractured instruments.

The electronic apex locator has helped cliniciansidentify the position of apical foramina more accu-rately; the development of this instrument made it possible to work more precisely and routinely as closeas 0.5mm to the canal terminus (see Chapter 8).

Concepts and Strategies

Two factors are closely related to the preparation length:use of a patency file and the apical width. A patency fileis a small K-file (usually a size #10 or #15) that is pas-sively extended just through the apical foramen.

Use of a patency file has been suggested for mostrotary techniques. This step is believed to remove accu-mulated debris and help maintain working length.However, the issue is controversial, and a large numberof U.S. dental schools did not teach this concept, at leastnot until recently.53 Moreover, Goldberg and Massone102

demonstrated that the use of patency files of varyingsizes did not prevent preparation errors.

One concern with the patency file was that instead ofhaving a cleaning effect, the file would push contami-nated debris through the foramen. However, a recent in vitro study suggested that the risk of inoculation was minimal when canals were filled with sodiumhypochlorite.133 No definitive evidence exists eitherfavoring or disproving the use of a patency file.However, clinical experience suggests that this techniqueinvolves relatively little risk and provides some benefitas long as small files are used carefully.

Like the position of the apical constriction, apicaldiameters are difficult to assess clinically.149 Some haverecommended gauging canal diameters by passing aseries of fine files apically until one fits snugly. However,such an approach is likely to result in underestimationof the diameter.314 This is a crucial point because theG

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initial canal size determines the desired final apicaldiameter.

An ongoing debate exists between those who prefersmaller apical preparations combined with taperedshapes and those who favor larger apical preparationsfor better removal of infected dentin and to allow irri-gation fluids access to the apical areas. Both sides stress

the importance of maintaining the original path of thecanal during preparation; otherwise, bacteria infectingthe apical third of the root canal may not be reached bya sufficient bactericidal concentration of an antimicro-bial agent.179 Investigators obtained a higher percentageof bacterial elimination in single-root canal systems byusing a combination of significant enlargement of the G

Fig. 9-42 Irrigation and the movement of irrigants depends on the canal shape. Sequential enlargement of a canal in clear plastic blockwas performed with a sequence of ProFile instruments in accordance with the manufacturer’s recommendations. Alternating irrigation withblue and red fluid was done after each preparation step. Note the apical presence of irrigant after sufficient shape has been provided. Notethe distribution of fluid immediately after irrigation with a 30-gauge needle.

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apical third and sodium hypochlorite irrigation.57

Preparation errors (e.g., zips, canal transportation) canoccur with wide preparations when either stainless steelor nickel-titanium instruments are used (see Fig. 9-44).

Thorough disinfection of the apical part of a rootcanal is essential, because this area is likely to containintraradicular bacteria.182 Wider apical preparationsremove potentially infected dentin, allowing the deliv-ering needle and subsequently the antimicrobial irrig-ant to penetrate the root canal more deeply.60

A study investigating rotary nickel-titanium files ofthree tapers (#.06, #08, and #.10) with file tips in sizes#20, #30, and #40 showed that size #20 instruments leftsignificantly more debris in the apical third comparedwith size #40 instruments.299 On the other hand, a studyin which half the samples were prepared to a size #25G

A

C

D

EB

Fig. 9-43 Example of a desired shape with the original rootcanal fully incorporated into the prepared outline. A and B, mCTreconstructions in clinical and mesiodistal views of a maxillary molarprepared with a NiTi rotary system. The green area indicates the pre-operative shape, and the red area indicates the postoperative shape.Areas of mixed red and green indicate no change (i.e., no removalof radicular dentin). C to E, Cross sections of the coronal, middle,and apical thirds; the preoperative cross sections (green) are encir-cled by the postoperative outlines (red) in most areas. (A and Bfrom Hübscher W, et al: Int Endodon J 36:740-747, 2000.)

B

Fig. 9-44 Schematic diagrams showing the most commonpreparation errors. A, Apical zip. B, Ledge. C, Apical zip with perfo-ration. D, Ledge with perforation.

A

C D

file and the other half to a size #40 file found no sta-tistically significant difference in bacterial growth afterinstrumentation, with no growth observed after 1 weekof treatment with a calcium hydroxide dressing.324

Another study compared step-down sequences withadditional apical enlargement to ISO size #35 or a serialstep-back technique with no apical enlargement. NaOCland EDTA were used as irrigants.65 No significant dif-ference was detected in colony-forming units with orwithout apical enlargement.65 These researchers con-cluded that dentin removal in the apical third might beunnecessary if a suitable coronal taper is achieved.

Despite the disagreement over the appropriate widthof a preparation (Table 9-2), it appears that root canalpreparations should be confined to the canal space,should be sufficiently wide, and should incorporate theoriginal root canal cross sections (see Fig. 9-43). Thisway, routine root canal treatment results in favorable outcomes at various levels of clinicians’ expertise (Fig. 9-46).

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CANAL PREPARATION TECHNIQUES

The traditional cleaning and shaping strategy (the step-back technique) focused on the initial preparation of the apical third of the root canal system, followed by various flaring techniques to facilitate obtura-tion.106,235,287 In an attempt to reach the canal terminus,the clinician first selected a small file, placed an appro-priate curve on the instrument, and then tried to work

the file to full length. If the terminus could not bereached, the file was removed and, after irrigation, eitherthe same file or a smaller one was inserted. However,more often then not full length could not be reachedbecause of blockage or coronal binding.

Coronal binding is caused by overhangs at the orificelevel and also occurs when the canal is less tapered thanan instrument, thus binding somewhere coronally.Moreover, a straight root often has a curved canal;buccal and lingual curvatures that cannot be seen onradiographs also need to be detected.66,207 Passing a pre-curved negotiating file through a coronally tight canalwill straighten the instrument.267 Nonflared canals donot allow efficient irrigation, which further predisposesto blockage.

Various instrumentation sequences have been devel-oped for hand and rotary instruments; these are dis-cussed later in the chapter. However, the shape of theaccess cavity is the prerequisite that must be optimizedbefore any canal preparation can take place (see Chapter7).

One approach to the preparation of an adequateaccess cavity (Fig. 9-47) involves the use of a cylindricdiamond or fissure bur, a safety-ended drill for addi-tional enlargement, and round burs to remove over-hangs on outward strokes. The access cavity shape mustallow instruments unimpeded access to the middlethird of the root canal system. Ultrasonically poweredinstruments used under an operating microscope greatlyfacilitate removal of mesial dentin shelves in mandibu-lar molars (Fig. 9-48, A and B) and other teeth. Preex-isting restorations allow for ideal access cavities thatserve as reservoirs of irrigants (Fig. 9-48, C).

Basic cleaning and shaping strategies for root canalpreparation can be categorized as crown-down, step-back, apical widening, and hybrid techniques. In acrown-down approach, the clinician passively inserts alarge instrument into the canal up to a depth that allowseasy progress. The next smaller instrument then is usedto progress deeper into the canal; the third instrumentfollows, and this process continues until the terminus is G

1.0 mm

1.0 mm

A

C

D

EBFig. 9-45 Example of excessive thinning of dental structureduring root canal treatment. A and B, mCT reconstructions show pre-operative and postoperative root canal geometry of a maxillarymolar. C to E, Cross sections of the coronal, middle, and apical thirdswith preoperative canal cross-sections. Note the transportation andthinning, in particular, in the main mesiobuccal canal.

Table 9-2 Benefits and Drawbacks of Wide and Narrow Apical Preparations

ROOT CANAL PREPARATION BENEFITS DRAWBACKS

Narrow apex Minimal risk of canal transportation, Little removal of infected dentinextrusion of irrigants, or extrusion Questionable rinsing effect in apical areas duringof filling material irrigation

Can be combined with tapered Possibly compromised disinfection during preparation to counteract some interappointment medicationdrawbacks Not ideal for lateral condensation

Wide apex Removal of infected dentinAccess of irrigants and medications Risk of preparation errors and of extrusion of

to apical third of root canal irrigants and filling materialNot ideal for thermoplastic obturation

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G

A B

C D

Fig. 9-46 Routine cases treated according to the principles discussed in this chapter. Biologic and mechanical aims were maintained atvarying levels of expertise. A, Asymptomatic tooth #18 with periradicular lesion; endodontic treatment was indicated. B, Recall radiographafter 18 months (treatment was performed by fourth-year student at Zurich Dental School). C, Preoperative radiograph of tooth #2, whichwas diagnosed with irreversible pulpitis. D, Recall radiograph 2 years later shows sound periradicular tissue; the tooth is clinically symptomfree (treatment was performed by an endodontist).

1 2 3

Fig. 9-47 Sequence of instruments used for optimal preparation of an access cavity (e.g., in an incisor). A parallel-sided diamond or steelbur is used to remove overlying enamel in a 90-degree angle toward the enamel surface (1). The bur is then tilted vertically to allow straight-line access to the root canal (arrow). A bur with a noncutting tip (e.g., Endo-Z bur or ball-tipped diamond bur) is then used to refine access(2). Overhangs or pulp horns filled with soft tissue are finally cleared with a round bur used in a brushing or pulling motion (3).

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reached. Both hand and rotary instruments may be usedin a crown-down manner. However, instrument setswith various tip diameters and tapers allow the use ofeither decreasing tapers or decreasing diameters forapical progress. Debate continues as to which of thosestrategies is superior for avoiding taper lock; currentlyno compelling evidence favors either of them.

In the step-back approach, working lengths decreasein a stepwise manner with increasing instrument size.This prevents less flexible instruments from creatingledges in apical curves while producing a taper for easeof obturation.

As discussed previously, the aim of apical wideningis to fully prepare apical canal areas for optimal irriga-tion efficacy and overall antimicrobial activity. Recently,apical enlargement has been broken down into threephases, preenlargement, apical enlargement, and apicalfinishing.304

Most rotary techniques require a crown-downapproach to minimize torsional loads36 and to reducethe risk of instrument fracture. Used sequentially, thecrown-down technique can help to enlarge canalsfurther. All basic techniques described so far may becombined into a hybrid technique to eliminate orreduce the shortcomings of individual instruments.

Root canal preparation can be broken down into aseries of steps that parallel the insertion depths of indi-vidual instruments. Anatomic studies and clinical expe-rience suggest that most teeth are 19 to 25mm long. Mostclinical crowns are approximately 10mm long, and mostroots range from 9 to 15mm in length. Roots, therefore,can be divided into thirds that are 3 to 5mm long.

Provided adequate tools are used and the accesscavity design is appropriate, excessive thinning of radic-ular structures can be avoided (see Fig. 9-45). Verticalroot fractures and perforations are possible outcomes ofexcessive removal of radicular dentin in zones that havebeen termed danger zones12: overenthusiastic filing, forexample, may lead to more procedural errors (see Fig.9-20). On the other hand, ideal preparation formswithout any preparation errors and with circular incorporation of the original canal cross sections maybe achieved with suitable techniques (see Fig. 9-43).

Preenlargement of the coronal half to two thirds toallow files unimpeded access gives the clinician bettertactile control in directing small, adequately precurvednegotiating files into the delicate apical third (Fig. 9-49). Gates-Glidden drills can be used sequentially toenlarge the coronal third of the canal in teeth withstraight roots (Fig. 9-50). Both step-back and step-downsequences have been recommended.

Besides Gates-Glidden burs, various instrumentshave been introduced or suggested for coronal preen-largement, such as the ProFile orifice shapers, GT acces-sory files, the ProTaper Sx, the FlexMaster Intro file, andthe size #40, #.10 taper or size #35, #.08 taper RaCe files.These instruments are better suited to and safer for moredifficult cases (Fig. 9-51).

Once the coronal portions of a canal have beenenlarged, the apical canal areas can be more efficientlyprepared. Better clinical results are obtained with opti-mized access, regardless of the preparation techniqueused (Fig. 9-52). Only after preenlargement can finescouting files (also used before rotary files in the coronal G

A

B

CFig. 9-48 Clinical views of an access cavity in a mandibularmolar as seen through an operating microscope. (¥20.) A, Modifi-cation with an ultrasonically activated tip. B, Access cavity after modification. C, Cavity is flooded with 1% sodium hypochlorite.

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areas) provide information about the root canal paths. Preenlarged canals may accommodate hand files, which can be used to gather specific informationabout the apical third’s cross-sectional diameter andanatomy.

Hand Instrumentation

General agreement exists that hand files should be usedfor the balanced force technique. Roane et al223

described this technique as a series of rotational move-ments for Flex-R files, but it can also be used for K-filesand other hand instruments, such as GT hand files.Many different explanations have been offered for theobvious and undisputed efficacy of the balanced forceapproach58,150,223; however, general agreement exists thatit provides excellent canal centering ability, superior toother techniques with hand instruments.16,42,153,225

The balanced force technique involves three or foursteps. The first step (after passive insertion of an instru-ment into the canal) is a passive clockwise rotation ofabout 90 degrees to engage dentin (Fig. 9-53). In thesecond step, the instrument is held in the canal withadequate axial force and rotated counterclockwise tobreak loose the engaged dentin chips from the canalwall; this produces a characteristic clicking sound. Clas-sically, in the third step the file is removed with a clock-wise rotation to be cleaned; however, because files usedwith the balanced force technique are not prebent, everylinear outward stroke essentially is a filing stroke andmay lead to some straightening of the canal path. There-fore, in many cases the clinician may advance fartherapically rather than withdrawing the file, depending onthe grade of difficulty.

NiTi rotary instruments are an invaluable adjunct inthe preparation of root canals, although hand instru-ments may be able to enlarge some canals just as effi-ciently when used in appropriate sequences (Fig. 9-54).

G

Fig. 9-49 Various prebent, stainless steel hand files for pathfind-ing and gauging. Compare the curves in the instruments to the onesin a plastic training block (gradation of ruler is 0.5 mm).

NaOCl

#10

GG4

GG3

NaOCl

GG2

GG1

#10

Fig. 9-50 Diagram of coronal enlargement in a maxillary anterior tooth. After preparation of the access cavity (Fig. 9-47) and copious irrigation, Gates-Glidden burs are used in a step-down manner to enlarge the orifice and provide straight-line access into the middle third of the canal. Prebent size #10 K-files are used to explore the canal path and dimension.

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G

NaOCl

#10

OS1

NaOCl

OS5 OS4

#10

OS3OS2OS3OS1

Fig. 9-51 Diagram of coronal enlargement in a more complicated maxillary posterior tooth. This maxillary molar presents several difficul-ties, including a narrow mesiobuccal canal that exits the pulp cavity at an angle. A possible approach in a case involving difficult entry intothe root canal system is to use a small orifice shaper (OS1) after ensuring a coronal glide path with a K-file. Use of a sequence of orificeshapers (OS3 to OS1) then allows penetration into the middle third of the root canal. Wider canals can accept a second sequence of orificeshapers. Copious irrigation and securing a glide path with a size #10 K-file are prerequisites for use of NiTi rotary instruments.

Hand instruments should be used only after coronalpreenlargement (e.g., with Gates-Glidden drills). Afterpreenlargement, the access cavity and canals are floodedwith irrigant, and a prebent scouting file is advancedinto the canal. A lubricant can help prevent apical block-age in this early stage. Once the working length has beenestablished (aided by an electronic apex locator andradiographically verified), apical enlargement to thedesired size begins (Fig. 9-55). As stated previously,various apical preparation designs exist, and the choiceis driven mostly by the desired obturation technique,whether an apical stop or an apical taper is prepared.Finally, canal taper is increased by decreasing theworking length of larger instruments in 1 or 0.5mmincrements, producing #0.05 and #0.10mm tapers,respectively.

Copious irrigation and frequent recapitulations with a smaller file to working length may be required,and in some instances clinicians must devise creativestrategies using small crown-down and/or step-backsequences.

In many cases hand instrumentation produces ade-quate shapes, but clinicians often choose NiTi rotaryinstruments either to enlarge curved canals or toproduce wider tapers. Fig. 9-56 illustrates the develop-ment of these shapes in the mesial root canals of amandibular molar, clearly showing that substantialareas of the root canal surface are not instrumented,even when apical size #50 or #.09 tapers are reached(red areas in Fig. 9-56, G and I).

Rotary Instrumentation

LightSpeed InstrumentSince the introduction of LightSpeed instruments, themanufacturer’s guidelines have changed17; this sectionpresents the current version248 (Figs. 9-57 and 9-58).

After coronal preenlargement with the instrument ofchoice, working lengths are obtained and apical enlarge-ment is done with at least a loose-fitting size #15 K-file.Apical canal diameters are then gauged by the insertionof LightSpeed instruments of increasing size until onebinds just before reaching the working length. Thisinstrument, which is then used in the handpiece, is thefirst LS instrument size to bind before reaching theworking length (the FLSB).

All LightSpeed instruments are used in the followingway: a slow, continuous apical movement is used untilthe blade binds; after a momentary pause, the blade isadvanced to the working length (WL) with intermittent(“pecking”) motions.248 The number of pecks requiredto reach the WL increases as instrument size increases,because more wall dentin is cut. The instrument sizethat requires 12 or more pecks (12-peck rule)248 toadvance from the point of first binding to the WL is themaster apical rotary size (MAR).

An instrument one size larger than the MAR then isused to instrument to a length 4mm short of theworking length. This shapes the canal for subsequentobturation with SimpliFill (LightSpeed Technologies).The middle third of the canal is instrumented withsequentially larger full-size instruments until a size is

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reached that cannot be easily advanced beyond thecoronal third. The midroot area usually is prepared withthree or four LightSpeed instruments. Finally, the MARis used to recapitulate to the working length (see Fig. 9-58).

ProFile Many different techniques have been advocated for theProFile,242 but the general pattern remains a crown-down approach with varying tapers and tip diameters.The ProFile therefore can be used as an example forsystems with this basic design (e.g., the HERO 642, K3,and FlexMaster). It must be noted that the manufactur-ers’ instructions for those systems are somewhat differ-

ent, and the instructions for GT rotary and RaCe filesvary even more. Therefore the clinician should alwaysread the manufacturers’ instructions for details onworking with those instruments. That being said, it alsomust be noted that the merits of specific instructionshave not been scientifically elaborated.

As with other instruments, coronal preenlargement ismandatory (see Figs. 9-51 and 9-52). The workinglength then is determined as described previously, andan open glide path is secured with K-files up to size #15or #20, depending on the canal anatomy. If canal sizepermits, canal preparation begins with #.06 taperinstruments in descending tip diameters36 (Fig. 9-59).In more difficult small canals, #.06 tapers are followedG

A B

C D

E FFig. 9-52 Clinical example of the importance of straight-line access to the middle third of the root canal. A, Preoperative radiograph oftooth #30, diagnosed with irreversible pulpitis. This tooth serves as a retainer for a metal-free, fixed partial denture. Note the prominentdentin shelves (arrows). B, Working length radiograph with hand instruments inserted into the mesial and distal canals. C, Cone-fit radiographshowing tapered preparations after removal of the dentin shelves. D, Posttreatment radiograph after thermoplastic compaction of gutta-percha.E and F, Follow-up radiographs at 2 and 4 years. The tooth is clinically symptom free, and the periodontal ligament appears to be withinnormal limits.

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G

≈90°

Step 1

180-270°

Step 2

≈90°

Step 3

360-720°

Step 4

Fig. 9-53 Diagram of handle movements during balanced force hand preparation. Step 1: After pressureless insertion of a Flex-R or NiTi-Flex K-file, the instrument is rotated clockwise 90 degrees using only light apical pressure.Step 2: The instrument is rotated counterclockwise 180 to 270 degrees; sufficient apical pressure is used to keep the file at the same inser-tion depth during this step. Dentin shavings are removed with a characteristic clicking sound.Step 3: This step is similar to step 1 and advances the instrument more apically.Step 4: After two or three cycles, the file is loaded with dentin shavings and is removed from the canal with a prolonged clockwise rotation.

NaOCl

#10 #10#15 #20 #10 #25 #30 #35 #40

NaOCl

NaOCl

1 ...

5 ...432

Fig. 9-54 Root canal instrumentation with hand files: Part I. After the orifice has been accessed (see Figs. 9-47 and 9-52) and copiousirrigation performed (1), the working length (WL) is determined. A size #10 and/or #15 K-file is advanced to the desired apical preparationendpoint, aided by an electronic apex locator (2). The apical canal areas are then enlarged with K-files (3) used in the balanced force tech-nique (see Fig. 9-53). Frequent, copious irrigation with sodium hypochlorite is mandatory to support antimicrobial therapy. Frequent recapit-ulation with fine K-files is recommended to prevent blockage (4). Apical enlargement is complete to the desired master apical file (MAF) size(5), which depends on preoperative canal sizes and individual strategy. Typically, size #40 or larger may be reached in anterior teeth, as inthis example. File sizes larger than #20 may be used with NiTi instruments (e.g., NiTiFlex).

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by #.04-tapered instruments, also with descending tipdiameters (Fig. 9-60). Apical preparation is performedeither with multiple shaping waves, as suggested for GTrotary files,47 or in a step-back manner.242 Because oftheir superior resistance to cyclic fatigue, #.02-taperedProFile instruments are useful for abrupt apical curves.Preparation is complete once a continuous #.06 taperwith an adequate apical size is achieved. Recapitu-lation during the preparation with a small hand file isrecommended.

ProTaper The approach for ProTaper instruments differs from that for most other NiTi rotary files in that no traditionalcrown-down procedure is performed (Fig. 9-61).

Size #10 and #15 hand files are precurved to matchthe canal curvature and then passively inserted into thecoronal two thirds of a root canal as pathfinding files,which confirm the presence of a smooth, reproducibleglide path. This step is essential for ProTaper shapinginstruments, because they are mostly side-cutting andhave fine, fragile tips.

Shaping files S1 and S2 are then passively insertedinto the scouted canal spaces, which have been filledwith irrigant (preferably sodium hypochlorite). If nec-essary, the SX file can be used at this stage to relocateorifices or remove obstructing dentin. After eachshaping file is used, the canals are reirrigated and a size#10 file is used to recapitulate to break up debris and

move it into solution. This process is repeated until thedepth of the pathfinding #10 or #15 file is reached.

After irrigation the apical third is fully negotiated andenlarged to at least a size #15 K-file, and the workinglength is confirmed (see Fig. 9-61). Depending on thecanal anatomy, the rest of the apical preparation can bedone with engine-driven ProTaper shaping and finish-ing hand files. As an alternative, handles can be placedon these instruments (Fig. 9-62) so that they can beused for the balanced force technique.

ProTapers S1 and S2 are then carried to the fullworking length, still in a floating, brushing motion. Theworking length should be confirmed after irrigation andrecapitulation with a K-file, aided by an electronic apexlocator and/or radiographs. Because of the progressivetaper and more actively cutting flutes higher up in theProTaper design, interferences in the middle andcoronal thirds are removed at this stage.

The preparation is finished with one or more of theProTaper finishing files, used in a nonbrushing manner;because of their decreasing taper, these files will reachthe working length passively. Recapitulation and irriga-tion conclude the procedures (see Fig. 9-61).

Most cases requiring root canal therapy lend them-selves to canal preparation with many different systems;depending on the individual anatomy and the clini-cian’s strategy, various sequences may be used. Fig. 9-63presents two cases that involved different problems andtherefore were approached differently. MesiobuccalG

NaOCl

#45 #10#50

#55

#10

#60#70

#80

#45

NaOCl NaOCl

1 ...

5 ...432

Fig. 9-55 Root canal instrumentation with hand files: Part II. Frequent irrigation with sodium hypochlorite (1) is more efficient after theworking length (WL) is reached, because irrigation needles may penetrate deeper into the canal. Canal taper is increased to further improveantimicrobial efficiency and to simplify subsequent obturation. Hand instruments are set to decreasing working length in 0.5-mm increments(step-back) from the master apical file (2 to 3). A fine K-file is used to recapitulate to WL during the procedure (4), and the MAF is used asa final recapitulation (5) to ensure that remaining dentin chips have been removed.

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Hybrid Techniques For some time some have suggested combining variousNiTi preparation systems to address certain shortcom-ings of current instruments.57,304 Although many com-binations are possible, the most popular and usefulones involve coronal preenlargement followed by dif-ferent additional apical preparation sequences.However, clinicians must keep in mind that anatomicvariations in each canal must be addressed individuallywith specific instrument sequences. Most important,oval canals extend deep into the apical area,276,312,315,316

and apical foramina in fact may be oval in most cases.41

Naturally, a rotating file can produce a round canal atbest; therefore, a strategy must be devised for adequatelyshaping oval canals without overly weakening radicularstructure (compare Figs. 9-43 and 9-45). One hybridapproach completely prepared 95% or more of all suchcanals and resulted in extremely wide apical sizes thatmay be difficult to achieve with most instrumentsystems140-143 (Box 9-5).

Histologic slides (see Fig. 9-39) and mCT reconstruc-tions (see Figs. 9-43, 9-45, and 9-56) show critical areasthat were not mechanically prepared despite the use

G

1 mmA

B

C

D

E

F

H

I

G

Fig. 9-56 Stepwise enlargement of mesial root canal systems inan extracted mandibular molar demonstrated with mCT reconstruc-tions. The buccal canal (left) was prepared with a LightSpeed (LS)instrument, and the lingual canal (right) was shaped with a ProTa-per (PT) instrument. A, Preoperative view from the mesial aspect.Note the additional middle canal branching from the lingual canalinto the coronal third. B, Initial preparation and opening of the ori-fices, aided by ultrasonically powered instruments. C, First step ofroot canal preparation, up to LightSpeed size #20 and ProTapershaping file S1. D, Further enlargement to LS size #30 and PTshaping file S2. E, Apical preparation to LS size #40 and PT finish-ing file F1. F, Additional enlargement to LS size #50 and PT finish-ing file F2. G, Superimposed mCT reconstructions comparing theinitial canal geometry (in green) with the shape reached after useof the instruments shown in F. H, Final shape after step-back withLS instruments and PT finishing file F3. I, Superimposed mCT recon-structions comparing initial geometry and final shape. Note theslight ledge in the buccal canal after LS preparation and somestraightening in the lingual canal after PT preparation.

roots of the maxillary molar can show substantial cur-vature; rotary instrumentation and/or hybrid tech-niques allow preservation of the curvature (Fig. 9-63, A)and optimal enlargement (Fig. 9-63, B). Often handinstruments other than ISO-normed files (see Fig. 9-62)are used in these cases to ensure a smooth, taperedshape or to eliminate ledges.

�

Box 9-5 Benefits of Using aCombination of Instruments forEndodontic Therapy

• Instruments can be used in a manner that promotestheir individual strengths and avoids their weaknesses(most important).

• Hand instruments secure a patent glide path.• Tapered rotary instruments efficiently enlarge coronal

canal areas.• Less tapered instruments allow additional apical

enlargement.

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G

NaOCl

#10

#35

#15

#20 #30 #32.5 #37.5 #40

NaOCl

1 ...

3 ... 42

Fig. 9-57 Preparation of a maxillary molar with LightSpeed (LS) instruments. After coronal enlargement with a tapered rotary instrumentor GG drills (Figs. 9-47 and 9-50) and irrigation with NaOCl (1), the working length is determined with a small K-file, aided by an electronicapex locator. A patent glide path is secured by hand instrumentation up to a loosely fitting size #15 K-file (2). The canal size is gauged byhand-held LS instruments, and the first LS size to bind (FLSB) is selected. Apical instrumentation is then begun with engine-driven LS instru-ments, starting with the FLSB (4) up to the desired apical size (see text for further explanation).

NaOCl

#42.5

#57.5

#45

#50

#52.5#55

#60

#42.5

1 ...

3 42

#47.5

5

Fig. 9-58 Finishing of LightSpeed preparations to allow obturation. With the canal system flooded (1), apical preparation (2) is continueduntil an LS instrument requires 12 pecks to reach the working length (WL). The next LS instrument (3) then is used to a point 4 mm shortof the WL to prepare for LightSpeed’s SimpliFill obturation system. Alternatively, canals may be flared for other root canal filling techniquesby preparing with each subsequent instrument 1 mm shorter (5).

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G

5 ...

NaOCl

#.06 40

#.06 35

#.06 25

#10

1 ...

3 42

#.06 30

#15

#.06 20

#.06 20

#.06 35

#.06 30

Fig. 9-59 ProFile instrumentation in a wider canal. In irrigated and flooded canals (1), a crown-down preparation is done with a sequenceof #.06-tapered ProFile instruments (2). When the apical third is reached, the WL is determined and a glide path is secured (3). Apical prepa-ration is then completed by continuing the crown-down sequence (4) up to the desired apical width at the WL. Several shaping waves maybe required (5).

5

NaOCl

#.06 25#.06 20

#.04 20

#10

1 ...

3 42

#.04 25

#15

#.04 20 #.06 20#.06 25

Fig. 9-60 Sequence of ProFile instruments used in constricted canals. After irrigation (1) and coronal preenlargement with orifice shapers(see Fig. 9-51), ProFile instruments size #25, #.06 taper; size #20, #.06 taper; and size #24, #.04 taper are used as crown-down instruments(2). After the WL has been determined and a glide path secured (3), apical preparation to the desired size begins (4). For additional taper,larger instruments may be used to a point short of the WL.

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G

5

NaOCl

#10

S1

#10

1 ...

3 42

S2

#15

S2 F1

S1

#15

Fig. 9-61 Instrumentation of root canals with ProTaper instruments. After irrigation and scouting (1 and 2), the coronal thirds are enlargedwith shaping files S1 and S2. Hand files then are used to determine the WL and to secure a glide path. Apical preparation is completed withS1 and S2. Finishing files are used to the desired apical width.

A B

C DFig. 9-62 Treatment performed with nickel-titanium rotary and hand instruments to eliminate instrument separation while maintainingbiologic aims. A, Preoperative radiograph of tooth #15. B, Postoperative radiograph shows a significant curvature in the mesiobuccal canaland additional anatomy in the lingual root. C, Preoperative radiograph of teeth #14 and #15. Both teeth were diagnosed with irreversiblepulpitis. D, Postoperative radiograph shows four canals in both of the treated maxillary molars. Note the wide apical preparation, particularlyin the curved mesiobuccal canals. (A and B courtesy Dr. T. Clauder; C and D courtesy Dr. H. Walsch.)

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of various individual rotary techniques. The aim ofhybridizing NiTi rotary techniques, therefore, is toincrease apical size using a fast and safe clinical procedure.

Various clinicians have used this type of hybrid pro-cedure in their practices (see Figs. 9-2, 9-5, 9-15, and 9-62). The technique involves the use of a variety ofinstruments: GG drills and K-files for establishingstraight-line access; ProTaper instruments for bodyshaping and apical preenlargement; NiTi K-files orLightSpeed instruments for apical widening; andvarious instruments for final smoothing.304

After a precurved, stainless steel file has confirmed asmooth glide path into the coronal two thirds, irriga-tion and mechanical preparation with a sequence ofProTaper files open and preenlarge the apical third (Fig.9-64). Once the working length has been established,the apical third is flooded with sodium hypochloriteand further enlarged with ProTaper finishing files F1and F2. The F3 ProTaper finishing file is relatively inflex-ible, and because of its side-cutting action, it should beused with caution in curved canals (Fig. 9-65).

The effectiveness of some hybrid techniques inenlarging canals recently was documented using super-imposed root canal cross sections (Fig. 9-66). This

approach can help identify insufficiently prepared areasand weakening of the radicular structure.

Some hybrid systems seem to work better thanothers, but the deciding factors seem to be the root canalanatomy and an adequate preparation goal.

If canal curvature is more severe, ProTapers may beused as hand instruments (see Fig. 9-63, A). Because thelargest ProTaper instrument has a size #30 tip, in manycases additional enlargement is desired. This may beaccomplished with LightSpeed or NiTi K-files (Fig. 9-67), which are first used to working length and then ina step-back approach. Finally, the overall shape may besmoothed with either engine-driven or hand-heldinstruments. Hand-held ProTaper or GT instrumentsmay aid removal of acute apical curvatures or ledges andprovide access to apical canal areas for irrigants.

Other Systems

Ultrasonically activated files or alternating file move-ments with special handpieces may be used to workcanal areas that rotary instruments cannot reach.However, to date no evidence shows that canal preparation with ultrasonic instruments is clinicallybeneficial. Similarly, neither traditional modified hand-pieces279 nor a recently introduced system (EndoEZEAET; Ultradent, South Jordan, UT) have been shown toallow preparation of adequate canal shapes.279

Ultrasonic devices have been linked to a higher inci-dence of preparation errors and to reduced radicularwall thickness.155 Newer analytic systems (e.g., mCT)allow tracking of the amount of dentin removed (Fig. 9-68); however, the amount of potentially infected dentinthat should be removed to maximize the chance of asuccessful outcome is unclear.

CANAL CLEANING TECHNIQUES

Irrigants and other intracanal medicaments are necessary adjuncts that enhance the antimicrobial effectof mechanical cleansing and thus overall clinical efficacy.50-52 Several studies205,206,277,312,317 have shown thatlarge areas of canal walls, particularly in the apical thirdbut also in ribbon-shaped and oval canals, cannot becleaned mechanically, meaning that microorganismspresent in these untouched areas could survive (see Figs.9-38, 9-43, and 9-45). Residual bacteria and othermicroorganisms exist both in these hard-to-reach spacesand in dentinal tubules.113,197,228 Chemical disinfection isan important cornerstone of a successful outcome,because it reaches bacteria or fungi present in dentinaltubules and in the crevices, fins, and ramifications of a root canal system.189,306 In one study, investigators prepared root canals, irrigated with saline solution, andsampled before, during, and after instrumentation.75

They then cultivated and counted colony-forming units. G

A

BFig. 9-63 Instruments with increased taper that can be used byhand. A, ProTaper instruments with special handles attached torotary instrument shanks. B, GT hand instruments.

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These researchers found that with instrumentationalone, progressive filing reduced the number of bacte-ria, regardless of whether rotary or stainless steel handinstrumentation was used. However, no techniqueresulted in bacteria-free canals. Siqueira et al257 con-firmed this finding; they found that instrumentationcombined with saline irrigation mechanically removed

more than 90% of bacteria in the root canal. Manyauthors have stressed the importance of using antimi-crobial irrigants during chemomechanical preparationto ensure complete disinfection.258

Substances that have been used to rinse and chemi-cally clean root canals have different purposes, such asdissolution of soft and hard tissues, antimicrobial effectG

NaOCl

#10

#10

1

3 42

GG3

#15

GG4

#15

5

Sx

NaOCl

Fig. 9-64 Hybrid technique: Part I. After irrigation (1) and scouting (2), GG drills (3) and/or ProTaper SX files (4) are used for coronalpreenlargement and to secure straight-line access to the middle third. Prebent K-files are then used to explore and determine the workinglength (5).

NaOCl

1

3 42

F1S2S1

NaOCl

F2 F3

NaOCl

Fig. 9-65 Hybrid technique: Part II. In canal systems flooded with irrigant (1), ProTaper shaping instruments S1 and S2 (2) and then fin-ishing instruments F1 and F2 (3) are used to preenlarge the apical third, allowing irrigants access to the canals. Finishing instrument F3 maybe used if feasible (4).

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against bacteria or other microorganisms in the rootcanal, and inactivation of bacterial lipopolysaccharides.These substances also should be as nontoxic as possibleto protect the periradicular tissues. Unfortunately, solu-tions that are toxic for bacterial cells frequently are toxicfor human cells as well; therefore, care must be taken toavoid extrusion of irrigants into periapical regions.43

Another critical factor is the volume of irrigant. In astudy evaluating the effect of different amounts offluids, the volume of irrigant was found to affect thecleanliness of the root canal.321 NaOCl and EDTAadministered in larger volumes produced significantlycleaner root canal surfaces than smaller volumes.321 Thechoice of an appropriate irrigating needle, therefore, isalso important. Although larger gauge needles allow theirrigant to be flushed and replenished more quickly, the wider needle diameter does not allow cleaning of

the apical and narrower areas of the root canal system(Fig. 9-69). Excess pressure or wedging of needles intocanals during irrigation, with no possibility of backflowof the irrigant, should be avoided under all circum-stances128 to prevent extrusion of the irrigant into peri-apical spaces. In juvenile teeth with wide apicalforamina or when the apical constriction no longerexists, special care must be taken to prevent resorptionor overpreparation of the root canal.70

Most root canals that have not been instrumented aretoo narrow to be reached effectively by disinfectants,even when very fine irrigation needles are used (see Figs.9-42 and 9-69). Therefore effective cleaning of the rootcanal must include intermittent agitation of the canalcontent with a small instrument173; this prevents debrisfrom accumulating at the apical end of the root canal(see Fig. 9-40). A suction system with a fine-caliber G

A1-A4

B1-B3

C1-C3

D1-D3Fig. 9-66 Effect of a hybrid technique on root canal anatomy studied in a Bramante model. A1 to A4, Both mesial canals of an extractedmandibular molar have been instrumented. Canal cross sections are shown before instrumentation (B1 to D1). B2 to D2, Cross sections afterpreenlargement with a ProTaper F3 file (left canal) and a size #45, #.02 taper instrument (right canal). The final apical sizes were LightSpeed(LS) #50 and size #50, #.02 taper in the left and the right canal, respectively. (Courtesy Dr. S. Kuttler, Dr. M. Gerala, and Dr. R. Perez.)

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suction tip may be a valuable adjunct for removing solu-tions and floating debris.

Disinfection

Different types of microorganisms, such as bacte-ria,136,178,179 yeasts,306,307 and possibly viruses,227 caninfect the pulp and may lead to apical periodontitis (seeChapters 14 and 24 and Fig. 9-7). These microorgan-isms must be reduced or eliminated to reestablish peri-radicular health. When bacterial samples test negativeafter treatment, the prognosis is improved.254,260 Duringmechanical root canal preparation, endodontic instru-ments are used to clean and enlarge root canal systems.Rotating instruments have an additional, advantageous“Archimedes screw” effect by which debris is trans-ported in an apicocoronal direction.75 Even whensimple saline was used as an irrigant, a tenfold to 1000-fold reduction of the bacterial load through mechanicalinstrumentation was demonstrated.52,75,190

However, as noted earlier, instrumentation alonedoes not produce a bacteria-free root canal. In onestudy, dentin samples tested positive in most of theteeth after mechanical instrumentation even thoughbacteria had been eliminated from the root canals insome cases.52 Bacteria persisted in seven root canalsdespite mechanical cleaning and saline irrigation duringfive consecutive appointments. Moreover, teeth with ahigh number of bacteria in the initial sample remainedinfected despite being treated five times.52 In anotherstudy, teeth that caused symptoms tended to have morebacteria than teeth with no clinical symptoms.190

Ørstavik and Haapasalo189 investigated the effect ofendodontic irrigants and dressings in standardizedbovine dentin specimens that were infected with testbacteria. They found that bacteria were capable of colonizing the canal lumen and dentinal tubules. In the specimens used, E. faecalis rapidly infected thewhole length of the tubules, whereas Escherichia colipenetrated approximately 600 mm. They also found that IKI appeared to be more effective at destroying bacteria than NaOCl, which was more effective thanCHX.

Other investigators have explored the effects ofsodium hypochlorite (with and without EDTA),chlorhexidine, and hydrogen peroxide in varying con-centrations when used in sequence or in combinationas endodontic irrigants.123 They found that chlorhexi-dine and sodium hypochlorite were similarly effectivein eliminating the bacteria tested. Synergistic effectswere observed for some of the irrigants (e.g., chlorhex-idine and iodine potassium iodide).

Both of the preceding studies used infected dentinspecimens; dentin is an important factor in disinfectionbecause certain concentrations of calcium hydroxidesolution, sodium hypochlorite, chlorhexidine, andiodine potassium iodide are inactivated or their activityis reduced by dentin powder112 (Fig. 9-70).

Some of the more difficult to remove endodonticpathogens, which can cause treatment failure, are ente-rococci and Actinomyces and Candida organisms29,182 (seeChapter 15). Table 9-1 presents the results of a numberof studies evaluating the effectiveness of some com-monly used antimicrobial agents.G

NaOCl

#32.5

#52.5

#35 #50

#52.5#50

#35

1 ...

3 42 ...

#47.5

5 ...

Fig. 9-67 Hybrid technique: Part III. Under irrigation (1), LightSpeed instruments may be used to enlarge substantially (2 and 3) and toflare the apical section (4). NiTi hand instruments (5) may be used similarly (see text for more detailed explanation).

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When reading literature about antimicrobial efficacy,clinicians must keep in mind that most disinfectingsolutions are inhibited or even inactivated by contactwith dentin or dentin powder during root canal prepa-ration.112,210 Moreover, chemical interactions occurbetween irrigation solutions; for example, NaOCl canbecome ineffective if it comes in contact with EDTA107

(Fig. 9-70).Currently, the endodontic irrigation solution with

the best proteolytic effect is NaOCl, even though it doesnot meet all the requirements of an ideal irrigant (Box9-6). It is readily available, inexpensive, and a widely G

Fig. 9-68 Reconstruction from mCT data (36 mm isotropic reso-lution) showing the amount of removed dentin by color coding.Maxillary molar shaped with ProTaper, apical size #25 (=F2) inmesiobuccal and distobuccal canals; palatal canal shaped to size#30 (=F3). The bar indicates the removed volume, expressed as thenumber of voxels. Note the red areas, which indicate dentin removalof more than 500 mm.

A B

C DFig. 9-69 Irrigation needles inserted into prepared root canals.A and B, A 27-gauge needle barely reaches the middle third. C and D, A 30-gauge, side-venting needle reaches the apical third (Fig. 9-40).

Storagetime

NaO

CI

Ant

imic

robi

al e

ffica

cy

Rinsingeffect

Volume(amount ofavailablechlorine)

HeatingChemicalinteraction

(EDTA)

Fig. 9-70 Interaction of sodium hypochlorite with various factorsthat determine its efficacy.

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G

Box 9-6 Properties of an Ideal Irrigantfor Root Canal Treatment

The irrigant should:• Be a highly effective disinfectant• Be nontoxic locally and nonallergenic• Differentiate between necrotic and vital host tissue• Retain its effectiveness with dental hard tissue and when

mixed with other irrigants

Fig. 9-71 Toxic effect of NaOCl on periradicular tissues. After rootcanal treatment of tooth #3, the patient reported pain. A, On areturn visit, an abscess was diagnosed and incised. B, Osteonecro-sis was evident after 3 weeks.

Fig. 9-72 Device for heating syringes filled with irrigation solu-tion (e.g., NaOCl) before use.

A B

used irrigation solution. Given sufficient time, NaOCl isa powerful solvent of necrotic pulp tissue and organicdebris and has excellent antimicrobial properties.Necrotic tissue and debris are dissolved by the break-down of proteins into amino acids through free chlo-rine in NaOCl. Concentrations used clinically rangefrom 0.5% to 5.25%. However, because free chlorine isthe important component, the solution must be replen-ished frequently during preparation to compensate forlower concentrations and to constantly renew the fluidinside the root canal. This is even more important whenthe root canal is narrow and small and files must carrythe NaOCl to the apical third during instrumentation(see Fig. 9-42). A 1% solution is effective at dissolvingtissue and providing an antimicrobial effect. The use ofcommercial household bleach in its undiluted form(5.25%) causes substantial necrosis of wound surfaceareas and may result in serious clinical side effects (Fig.9-71). It is diluted in 1:1 or 1:3 ratios with water toproduce a 2.5% or 1% solution; both are suitable forclinical endodontic use.269,328,331

As stated earlier, irrigation needles should never bewedged into canals during irrigation to avoid extrusionand serious damage to periapical tissues.43 Higher con-centrations of NaOCl are more aggressive toward livingtissue and can cause severe injuries when forced into theperiapical area (Fig. 9-71).

Such accidents can be prevented by marking theworking length on the irrigation needle with a bend ora rubber stop and by passively expressing the solutionfrom the syringe into the canal (see Fig. 9-69). Theneedle should be continuously moved slightly up anddown. It should remain loose in the canal, allowing abackflow of fluid. The goal is to rinse the suspended,concentrated dentinal filings out of the pulp chamberand root canals as new solution is brought down intothe most apical areas by the endodontic instrument andthe capillary effect.

Patency files should be used carefully and should not be extended farther than the periodontal liga-ment, because they are possible sources of irrigantextrusion.

In one study, heating increased the antibacterialaction of NaOCl.67 This can be done in several ways; forexample, after the solution has been drawn into the irri-

gating syringe, a syringe warmer can be used (e.g.,Syringe Warmer [Vista Dental Products, Racine, WI])(Fig. 9-72). Heating also enhanced the antibacterialeffectiveness of CHX and Ca(OH)2 solutions.88 A 0.5%NaOCl solution heated to 113∞ F (45∞ C) dissolved pulptissue as efficiently as a 5.25% solution used as the pos-itive control (Fig. 9-73). Heating to 140∞ F (60∞ C)resulted in almost complete dissolution of tissue.Studies have shown that 1 minute at 116.6∞ F (47∞ C) isthe cutoff exposure at which osteoblasts can still survive;however, higher temperatures may in fact be sufficientto kill osteoblasts and other host cells.86,87 Also,warming of NaOCl to 122∞ F (50∞ C)32 or 140∞ F (60∞C)4 increases collagen dissolution and disinfectingpotential, but it may also have severely detrimentaleffects on NiTi instruments, causing corrosion of themetal surface after immersion for 1 hour (Fig. 9-74).

An increase in the temperature of the irrigant may bea reason to include ultrasonic devices in canal irrigation;these devices also increase the tissue-dissolving capabil-ities of sodium hypochlorite.4,32 In one study, the peakirrigant temperature during use of an ultrasonic devicereached 113∞ F (45° C) near the file tip but remained at89.6∞ F (32° C) on the outer root surface of teeth pre-

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pared to a size #45.54 Another reason for using ultra-sonic devices might be enhancement of canal cleanli-ness. However, some authors have reported nobeneficial effect with ultrasonics, neither in debridingroot canal walls71 nor in reducing bacterial counts.78

A recent study corroborated these mixed findings173; in this study, smear layer removal with and withoutultrasonics after canal preparation with LightSpeed and ProFile rotary instruments did not differ significantly.

Smear Layer Management

EDTA is a decalcifying, chelating agent used as a gel ora 17% buffered solution during instrumentation of rootcanals. It acts as a chelator with calcium ions andremoves the dentinal debris produced on the root canalwalls during preparation. It thus opens dentinal tubules,allowing better penetration of disinfectants.104,129,289

Whenever the wall of a root canal is instrumented,whether by hand or rotating instruments, the parts of adentin wall touched by an instrument are covered by asurface layer called the smear layer.174,193 The smear layer,which consists of dentin shavings, cell debris, and pulpremnants,247 can be described as itself having two sepa-rate layers; a loose superficial deposit and an attachedstratum that extends into the dentinal tubules, formingoccluding plugs.56

For some time clinicians and researchers paid littleattention to the smear layer, partly because it was a thinsuperficial layer (1 to 5 mm) that might be present ornot, depending on the type of instrument and the sharp-ness of its cutting blades.247 Also, because acids andchelating agents dissolve the smear layer, it was re-moved and escaped attention in routinely processedspecimens (Fig. 9-75).72 Smear layers are not seen inunprepared canal areas, which may have calcospherites,buttonlike structures that are abundant on intracanalsurfaces.

Some authors have reported that an overlying smearlayer delays but does not eliminate the effect of medica-ments.189 Others contend that a smear layer mayadversely affect disinfection and may also increasemicroleakage after canal obturation.247 Althoughorganic substrate in a smear layer may serve as a nutri-tion source for some species of bacteria,39,194 some havesuggested that, conversely, a smear layer can act as a ben-eficial barrier, preventing microorganisms from enteringthe dentinal tubules when a root canal is colonized bybacteria between appointments.80 The potential of intra-canal disinfectants has been evaluated in vitro afterremoval of the smear layer with a combination of 5.25%sodium hypochlorite and 17% EDTA.113 The decalcify-ing effect of EDTA is self-limiting; therefore the solutionmust be replaced at intervals.129 EDTA can help openvery narrow root canals and can decalcify to a depth ofapproximately 50 mm. Because the smear layer consists G

120

5.25% @ 20°C

20°C

Dis

solv

ed ti

ssue

(%

)

45°C 60°C

100

80

60

40

20

0

Fig. 9-73 Effect of heating on the ability of 0.5% NaOCl to dis-solve pulp tissue. NaOCl heated to 113∞ F (45∞ C) dissolved pulptissue as well as the positive control (5.25% NaOCl) did. When theNaOCl was heated to 140∞ F (60∞ C), almost complete dissolutionof tissue resulted. (From Sirtes and Zehnder, unpublished data.334)

A

B

100 �mx100 12kV unikoeln #0222

100 �mx400 12kV unikoeln #0224

Fig. 9-74 Corrosion of nickel-titanium files in heated sodiumhypochlorite. A, Rotary instrument immersed for 2 hours in NaOClheated to 140∞ F (60∞ C). B, Magnification of rectangular area in A,showing severe corrosion.

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of organic and inorganic components, alternating use ofNaOCl and EDTA is most effective.

Liquid disinfectants were effective against E. faecalisin dentinal tubules up to depths of 400 mm. Microbio-logic analyses of split root halves showed that earlyremoval of the smear layer resulted in significantlyhigher bacteria counts.80 In contrast, other researchershave acknowledged that the smear layer, while acting as a barrier, might block irrigation solutions from entering the dentinal tubules.24 Moreover, some bacte-ria (e.g., Bacteroides gingivalis and Treponema denticola)have the potential to dissolve smear layer proteins,297

thereby producing gaps, which could promote bothcoronal and apical microleakage and bacterial multiplication.

Fig. 9-76 shows root canal cross sections with verylittle debris; irrigating solutions can penetrate the denti-nal tubules in this example. Some reported that thepresence of the smear layer had no significant effect onapical leakage in dye penetration test.89,168 Othersdescribed an improved seal after removal of the smear

layer.25,278 The latter study, which used a coronal leakagemodel, found a significantly decreased incidence of bac-terial penetration (30% versus 70%) when the canalswere irrigated with 17% EDTA and 5.25% NaOCl beforeobturation. In obturated root canals, a remaining smearlayer led to bacterial leakage in 60% of the samplesversus no leakage when the smear layer was removed.64

Other authors had similar results after smear layerremoval with EDTA solution alone. Another investiga-tion289 described many lateral canals in the apical thirdsof the root canals systems cleaned with a barbed broachwrapped with MTAD-soaked cotton and showed lesserosion than when EDTA was used. Other studies havefound that a stronger bond was present when the smearlayer was removed,98 and a statistically significant reduc-tion of microleakage was measured.82,232,233 However,another investigation reported increased apicalmicroleakage of the filled root canal after removal of thesmear layer.286

As shown in Fig. 9-41, dye staining is improved whenthe dentinal tubules are opened and the smear layer isremoved with EDTA, at least in the two more coronallevels. Although the effect of the smear layer on leakagehas been widely studied, its removal from root canalwalls remains controversial. The apparently conflictingG

30 �m

100 �m

A

BFig. 9-75 Prepared root canal surfaces after irrigation, showingvarying degrees of smear layer. A, Scanning electron micrograph(SEM), ¥25 showing prepared areas with and without open denti-nal tubules. The presence of calcospherites indicates that nomechanical preparation has been done laterally (arrow). B, SEM,¥400, showing thin, homogenous smear layer and scattered debrisin a canal that received a final sequence of a high-volume flush of17% EDTA followed by 2.5% NaOCl.

100 �m

100 �m

A

BFig. 9-76 Example of canals with minimal smear layer. A, Middlethird after irrigation with 17% EDTA and 2.5% NaOCl. B, Apical thirdwith some particulate debris.

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results of studies could stem from differences in thevarious microleakage test models318 and from differentobturation and irrigation techniques. The problem ofcoronal leakage has received much attention as a majorfactor in determining the success or failure in root canaltherapy.29,217,219,220,293

In general, it seems beneficial to remove the smearlayer in the later phases of endodontic therapy ratherthan during the early phases.

Research continues on ways to improve the effective-ness of irrigation. For example, tensides were added toirrigants more than 20 years ago to reduce their surfacetension, thereby improving wetability.5 The rationale forthis increased wetability was to improve the penetrationof irrigants into the dentinal tubules277 (this concept isstill pursued with MTAD today). One irrigating “cock-tail” investigated was a mixture of 5% NaOCl and 17%EDTA with the tensioactive chemical Triton X-100; thissolution was used with ProFile instruments.96 The studyreported that apical smear layer scores were significantlylower compared with those of control groups when thetensioactive agent was used throughout the preparationprocess.

In two in vitro studies, the noninstrumentation tech-nique, which relies on activated irrigation solutionsrather than mechanical preparation, produced excellentcanal cleanliness165,166 (Fig. 9-10, A). However, prelimi-nary clinical studies identified a need for improvementbefore this system can be used routinely to clean rootcanals.15

For the time being, root canals must be mechanicallyenlarged. Larger apical preparations enhance the efficacy

of irrigation, and the additional use of ultrasonic energyduring cleaning and shaping may also increase the efficacy of endodontic irrigants.56,69,152 Ultrasonics usedpassively in canals with sufficiently large apical prepa-rations may reach and better clean any uninstrumentedcanal areas.162,315,319 One investigation studied thedebriding ability of 2.5% NaOCl in canal recesses.68,69

In 10 of 11 cases, these researchers found significantlycleaner histologic sections after ultrasonically activatedirrigation. In the ultrasonically treated group, the bac-teria count was reduced by 99.8%. However, hand filingalone reduced the bacteria count by 99.3%; thereforethe improvement from ultrasonic therapy was limited.With ultrasonics, root canals are debrided by shearstresses produced between the irrigant and the canalwall, with subsequent cell disruption.8

Acoustic streaming of the irrigation fluid throughultrasonic treatment has been suggested as a method ofimproving cleanliness. However, this effect occursmainly in the most coronal levels; the apical areas wereleast affected by activated irrigation59,173 (Fig. 9-41).Because the amplitude of the oscillation is greatest atthe instrument’s tip, attenuation and constraint mostsignificantly affect the apical part,303 where the diameterof the canal is smallest.

One investigator reported that the most effectiveregimen with ultrasonic energy was to activate everydose of irrigant placed in the canal.55 With thisapproach, roughly 18 minutes of irrigation is requiredper canal. Other investigators used an irrigation time of1 minute each for EDTA and NaOCl, which seems clin-ically more practical.173 These authors stated that the use

G

A,B

D,E F

C

Fig. 9-77 Clinical cases treated according to the principles detailed in this chapter. A, Preoperative radiograph of tooth #30 with a peri-radicular lesion. B, Postobturation radiograph. C, Two-year follow-up radiograph shows osseous healing. D, Immediate postobturation radiograph of tooth #29 shows both a periapical and a lateral osseous lesion. E and F, One-year and three-year follow-up radiographs show progressing osseous healing. Note the imperfect obturation of tooth #30.

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of ultrasonic energy for irrigant activation did notimprove debridement compared with control groups.However, bacterial species show varying degrees of sus-ceptibility to ultrasonication.7,21,172,263

Because of the conflicting evidence concerning theeffectiveness of ultrasonics in root canal therapy, othermethods of disinfecting and debriding canals properlymust be studied. Such research might include betterways to deliver irrigants and disinfecting solutions.

SUMMARY

Cleaning and shaping are important, interdependentsteps in root canal treatment. Cleaning, as demonstratedby an intracanal surface free of smear layer, can be doneonly after root canals have been sufficiently enlarged toaccommodate adequate irrigation needles. Canal prepa-ration is optimized when mechanical aims are fulfilledand enlargement is acceptable; such aims include avoid-ing both significant preparation errors and weakeningof the radicular structure, which can result in fractures.

Taken together and performed to a high standard, theprocedures described in this chapter lay the foundationfor biologic success in both straightforward (Fig. 9-77)and more complicated (Fig. 9-78) clinical cases. Recallradiographs confirm favorable outcomes, or biologicsuccess (i.e., the prevention or healing of periradicularperiodontitis) over the years. Similarly, adherence to theprinciples discussed leads to predictable outcomes forroot canal treatments.

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Cleaning and Shaping of the Root Canal Systemkhotanpublishing.com/UploadedFiles/PFiles/560545045d73486.pdf · The stereotypic pulpal defense reaction is hard-tissue deposition (Figs