Modern Endodontic Practice

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MODERN ENDODONTIC PRACTICE

CONTENTS

Preface xiSyngcuk Kim

Modern Endodontic Practice: Instruments and Techniques 1Syngcuk Kim

Like many other dental and medical specialties, endodontics hasevolved and changed over the years. The changes that have oc-curred in the last 10 years, however, have been of great magnitudeand profundity. The microscope, ultrasonic units with specially

configured tips, superbly accurate microchip computerized apexlocators, flexible nickel-titanium files in rotary engines, and greateremphasis on microscopic endodontic surgery have totally changedthe way endodontics and endodontic surgery are practiced. Com-paring these changes with formocreosol medication, K-file andradiographic determination of working length are truly dramatic.These changes are bringing the specialty of endodontic practiceinto the twenty-first century with greater precision, fewer proce-dural errors, less discomfort to the patient, and faster case comple-tions. Seven key advancements in endodontics were made in thelast decade. This article discusses these advancements and their

applicability to everyday practice.

The Microscope and Endodontics 11Syngcuk Kim

The incorporation of the microscope in clinical endodontics hashad profound effects on the way endodontics is done and has chan-ged the field fundamentally. This article outlines the key prerequi-sites for the use of the microscope in nonsurgical endodonticprocedures, discusses which procedures benefit from using themicroscope, and addresses the issue of cost versus patient benefit.

Nonsurgical Ultrasonic Endodontic Instruments 19Mian K. Iqbal

The advent of nonsurgical ultrasonic tips has opened up a new hor-izon in endodontic treatment. There are a number of nonsurgical

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endodontic ultrasonic systems currently available in the marketand it is difficult to review all of them. Based on similarities amongdifferent instrument systems, an attempt has been made to classifyinstruments into broad categories. This article describes the utilityof each type of ultrasonic tip and the principles behind its usage.

These instruments may be area specific or use specific, but canbe used in an area other than the one for which they are specificallydesigned if the general principles regarding ultrasonic tips areunderstood and applied.

Electronic Apex Locator 35Euiseong Kim and Seung-Jong Lee

Locating the appropriate apical position always has been a challenge

in clinical endodontics. The electronic apex locator (EAL) is used forworking length determination as an important adjunct to radiog-raphy. The EAL helps to reduce the treatment time and the radiationdose, which may be higher with conventional radiographicmeasurements. According to recent publications, the accuracy offrequency-dependent EALs appears to be much higher comparedwith traditional-type EALs (simple resistance type or impedancetype). This article reviews the history and the working mechanismof the currently available EALs, and suggests the correct usage ofthe apex locator for a better canal length measurement.

Nickeltitanium: Options and Challenges 55Michael A. Baumann

The introduction of nickeltitanium (NiTi) as material for endodon-tic instruments about 15 years ago opened many new perspectives.Many dentists and scientists see a benefit in using NiTi files. Initialproblems such as frequent fractures and the uncertainty of the bestway to use them have been solved. Other challenges such as en-hancing the cutting ability or optimizing the speed, torque, and fa-

tigue are currently being addressed. Some clinicians are skepticalbecause they see this approach as too mechanical. Nevertheless,the combination of anatomic, biologic, and pathophysiologicknowledge with the use of NiTi instruments is a large step forwardin optimizing the quality of root canal treatment worldwide.

The ProFile System 69Yeung-Yi Hsu and Syngcuk Kim

The ProFile instruments were among the first nickeltitanium(NiTi) instruments to be marketed. This article describes theunique file design, clinical performance, safety concerns, and clin-ical applications of this system. Guidelines for NiTi rotary instru-ment usage need to be followed to minimize complications andmaximize benefits.

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manage individual clinical situations to achieve the best biomecha-nical cleaning and shaping results and the least procedural errors.The hybrid concept combines the best features of different systemsfor safe, quick, and predictable results. Several hybrid instrumenta-tion sequences are presented and their limitations are discussed.

Obturation of the Root Canal System 203Samuel I. Kratchman

With all the new technology that has been introduced in endodon-tics, there are now several ways to instrument and obturate rootcanals. Practitioners often develop their own hybrid techniqueafter sharing ideas with several colleagues. The purpose of thisarticle is to describe a technique of obturation, hoping that othersmay incorporate some aspects into their own hybrid style.

MicroSeal Systems and Modified Technique 217Francesco Maggiore

The MicroSeal technique was introduced in 1996 and consists of anickeltitanium (NiTi) spreader, a NiTi condenser, a gutta perchaheater, a gutta percha syringe, and a special formulation of guttapercha available in cones or in cartridges. It is considered a thermo-mechanical compaction technique that uses a rotary instrument to

plasticize the gutta percha and move it within the root canal api-cally and laterally. The MicroSeal technique together with theauthors modifications may be a very important tool in the handsof the endodontist. The MicroSeal system is able to preserve a con-servative preparation and provide an adequate penetration by theobturation instruments in the apical third. Knowledge of the techni-ques indications and limitations represents an important step in thelearning curve for those practitioners who are willing to incorporatea new obturation method into their clinical techniques.

Conventional Endodontic Failure and Retreatment 265Ralan Wong

Technologic advancements in dentistry and specifically endodon-tics have vastly improved the quality of care rendered to patients.These advancements allow clinicians to gain insight into the re-treatment of failing root canals. Due to training, practice, and pa-tience, clinicians can expand their capabilities alongside of thesetechnologic advancements to perform endodontic retreatmentswith increased success.

Perforation Repair and One-step Apexification Procedures 291Samuel I. Kratchman

As with any dental treatment, procedural mishaps can occur duringroot canal therapy. One such occurrence is the perforation of a root

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or pulpal floor. After a perforation occurs, the goals are to sterilize(decontaminate) the site and then seal the perforation. The materialmost widely used in endodontics to seal perforations is mineraltrioxide aggregate (MTA). MTA is extremely biocompatible, andit has been shown histologically that osteoidlike material grows

right into MTA. The technique of one-step apexification offers an al-ternative to drawn-out cases with several medicament-changingappointments that often result in a failed attempt at root-end clo-sure. With the favorable histologic response of MTA, this materialis the best current choice for this procedure. Completion of thesecases in an effective and efficient way allows for permanent restora-tions to be done in a more timely manner, prolonging the longevityof these teeth.

Modern Office Design in the Information Age 309

Garrett Guess

This article reviews the process of reaching the goal of modernizinga new or existing endodontic office. Incorporating computer-basedtechnologies in the office requires significant planning, best achie-ved by forming a technology goal that addresses budget, knowl-edge base, and infrastructure issues. Making the transition to themodern dental practice is expensive and time-consuming but alsoprofitable and exciting. Soon, all dental offices will be using digitalradiographic systems, video systems, and patient charting pro-grams that use no paper documentation. As the computer familiar-ity and staff knowledge base increases with the growing use ofcomputers in society overall, finding the office personnel able toharness the efficiency and power of the technology in the dental of-fice will be easier. Through careful planning and formation of a rea-sonable technology goal, updating an old office or creating a newmodern endodontic practice with the technologies of today canbe an enjoyable reality from which clinicians and their patientscan benefit.

Endodontic Working Width: Current Concepts and

Techniques 323Yi-Tai Jou, Bekir Karabucak, Jeffrey Levin, and Donald Liu

Root canal morphology is a critically important part of conven-tional and surgical endodontics (root canal therapy). Many in vitrostudies have recorded the scales and average sizes of root canals,but there have been few clinical attempts to determine the workingwidth. In the absence of a study that defines what the originalwidth and optimally prepared horizontal dimensions of canalsare, clinicians are making treatment decisions without any support

of scientific evidence. This article provides definitions and perspec-tives on the current concepts and techniques to handle workingwidththe horizontal dimension of the root canal systemandits clinical implications.

Index 337

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Preface

Modern endodontic practice

Guest Editor

The purpose of this issue of the Dental Clinics of North America is toinform our dental colleagues about the advancements of the theories and

techniques of modern nonsurgical endodontics. The microscope, nickel

titanium rotary file systems, and the electronic apex locator have profoundly

changed endodontic techniques. As a result, the modern endodontic spe-

cialty practice has little resemblance to the traditional endodontic practice.

We, at the University of Pennsylvania (Penn), have been very fortunate to

assemble a group of young, forward-looking clinicians and academicians

from around the world to establish truly modern endodontic treatment con-

cepts and modalities. It has been a global effort. Many of these Penn Endograduates, who contributed significantly to the advancements while at Penn,

are now teaching and practicing in different parts of the world and have

shared their ideas, experiences, and philosophies generously for this issue.

They are not only experts in their field in their countries but many are also

pioneers in this changing field. For that, this editor is extremely grateful.

The first article describes the way modern endodontics is practiced in an

endodontic specialty practice, briefly touching on the subject matter of each

article. In subsequent articles, the authors discuss the new generation of

instruments and new techniques in significant detail so that the readers candevelop a working understanding of the techniques. The clinical benefits of

the new treatment modalities far exceed our expectations. Cases are com-

pleted with greater precision, in less time, and with far fewer flare-ups

between visits. It is the rare patient who experiences discomfort or clinical

Syngcuk Kim, DDS, MPhil,PhD, MD (hon)

0011-8532/04/$ - see front matter 2004 Elsevier Inc. All rights reserved.

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complications. Twenty-first century endodontics is no longer the most

dreaded experience anyone can imagine, but mostly a pain-free, efficient

procedure with a predictably successful outcome.I hope that readers share our excitement about the truly new and

improved endodontics and our commitment to its practice.

I would like to thank Mrs. Jutta Do rscher-Kim at the University of

Pennsylvania for her invaluable assistance in editing and Mr. John Vassallo

of W.B. Saunders Company for initiating this project and for his patience

and support.

Syngcuk Kim, DDS, MPhil, PhD, MD (hon)

Department of EndodonticsSchool of Dental Medicine

University of Pennsylvania

240 South 40th Street

Philadelphia PA 19104-6030, USA

E-mail address: [email protected]

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mailto:[email protected]:[email protected]


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Modern endodontic practice: instruments

and techniques

Syngcuk Kim, DDS, MPhil, PhD, MD(hon)Department of Endodontics, School of Dental Medicine, University of Pennsylvania,

240 South 40th Street, Philadelphia, PA 19104-6030, USA

The specialty of endodontics has evolved and changed over the years like

many other dental and medical specialties. The changes that have occurred

in the last 10 years, however, have been of great magnitude and profundity.

The microscope, ultrasonic units with specially configured tips, superbly

accurate microchip computerized apex locators, flexible nickel-titanium files

in rotary engines, and greater emphasis on microscopic endodontic surgery

have totally changed the way endodontics and endodontic surgery arepracticed. Comparing these changes with formocreosol medication, K-file

and radiographic determination of working length are truly dramatic. These

changes are bringing the specialty of endodontic practice into the twenty-

first century with greater precision, fewer procedural errors, less discomfort

to the patient, and faster case completions.

Seven key advancements in endodontics were made in the last decade. In-

depth discussion of each of these advancements is found in articles elsewhere

in this issue. In this article, the advancements and their applicability to

everyday practice are discussed (Fig. 1).

The microscope

The previous issue of theDental Clinics of North Americawas devoted to

the use and advantages of the microscope. Briefly, the microscope provides

great magnification and illumination and functions as an extension of loupes

(Fig. 2). The proper use of the microscope in endodontic therapy provides

an advantage over any other tools. The question of why we need loupesor microscopes can be answered quite simply: loupes provide 2 to 4

magnification. Although small, this magnification has such an impact that

E-mail address:[email protected]


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Fig. 1. Key instruments for the modern practice. (A) Electronic apex locator. (B) Nickel-

titanium rotary ProFiles. (C) System B. (D) Spartan Piezo ultrasonic instrument. (E) Obtura II.

Fig. 2. The bright focused light and high magnification provided by the microscope results in

endodontics of the highest, most accomplished level.

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anyone who is used to loupes cannot practice without them. The microscope

provides 4 to 25 magnification. The questions here are, Do we needmagnification that great? and, in extension, What is the optimum

magnification for endodontic procedures? In the authors opinion, the opti-

mum magnification for endodontic practice ranges from 8 to 24 magni-

fication (Fig. 3). The high magnification is needed to locate hidden canals,

detect microfractures, distinguish between the chamber floor and dentin, and

identify isthmuses and other small anatomic entities, of which recognition

and treatment are so important for endodontic therapy success.

In conventional endodontics, the microscope is most useful for locating

canals after the access is made. It is extremely useful for post removal usingultrasonic instruments and for perforation repair. These are procedures that

previously were done largely by feel. The advent of the microscope in

modern endodontic therapy facilitates a primarily visually guided, second-

arily sensory-aided endodontic procedure (Fig. 4).

Ultrasonic instruments

There are two types of ultrasonic tips on the market: surgical andnonsurgical.

Surgical tips are for root canal retropreparation, and there are many types

available (see the Obtura/Spartan Company Web site, Fenton, Misssouri).

Nonsurgical tips come in two categories. First, the Buc tip is used for

conventional cases such as cleaning the chamber so that endodontists can

visualize the chamber without dentin debris (see the article by Kim elsewhere

Fig. 3. A completely instrumented madibular first molar at 4 magnification (A). The same

tooth at 24magnification (B) that shows dentin covering the pulpal floor. After removal of the

dentin, another canal is located and instrumented (C).

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in this issue, [Fig. 8]). The sharp-ended tips allow clinicians to pick and

explore the chamber floor to identify canals. This ultrasonic instrument isa lifesaver when calcified canals are encountered. High- or low-speed burs are

much too large to catch the minute, sometimes microscopic, openings to

calcified canals. A second type of nonsurgical ultrasonic tip is the CPR tip.

These tips are used mainly for post removal. Although posts can be removed

with burs, even the smallest burs unnecessarily remove large amounts of

dentin compared with CPR tips. Over 90% of the post can be removed by

CPR tips driven by a Piezo ultrasonic instrument, with much less gouging or

damaging the dentin structure around the post than with burs.

Cleaning the pulp chamber is also an important prerequisite for inspectionof the chamber for anatomic details. This cleaning can be done best with

a diamond-coated small microburner tip (eg, Buc tip size 2). Microscopic

observation is not effective when the chamber floor is full of dentin debris

that is created by burs.

Electronic apex locator

If asked what the most important advancement in endodontics in therecent decade is, the authors unequivocal answer would be the electronic

apex locator (seeFig. 1A). After the microscope, the electronic apex locator

has become the most important and essential instrument in endodontic

practice. Advancements in microchip technology led to the design of a better

apex locator, making the radiographic determination of root canal length

nearly obsolete. The correct use of the locator always identifies the root end

Fig. 4. The microscope is best used for repair of perforation (A), identification or detection of

microfractures (B), and removal of posts and/or separated files (C).



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correctly. This precision is needed to minimize intervisit flare-ups, over-

fillings, and underfillings. In the authors department, postgraduate students

rely more on their apex locators than on radiographs. This practice hascontributed greatly to pain-free treatments without flare-ups and with long-

term healing successalmost impossible 10 years ago.

System B or Touchn Heat

In the old daysonly 10 years agoa torch or open flame was used to

sear or melt the gutta percha. This technique is now called Flintstone-age

endodontics. The System B and Touchn Heat (SybronEndo, Orange,

California) allow a safer means to heat the gutta percha (see Fig. 1C).Specially designed tips of varying sizes are connected to the System B and

are heated instantly to the desired temperature by touching a sensor on the

handle. A tip is inserted into the obturated canal, the sensor to heat the tip is

activated, and the gutta percha is thermoplastesized. This thermoplastesized

gutta percha is then condensed (eg, with S-Kondensers) to obturate the

canal. It has been shown that the resulting temperature elevations within the

canal do not damage the periodontal ligament. The obturation technique

using System B is gaining popularity among endodontists and is gradually

replacing the old technique.

Obtura compactor

The Obtura compactor is another innovation in modern endodontic

practice that has become a must have. Thermoplastesized gutta percha

was used in endodontics before the invention of this compactor; however,

the procedure was done in the canal using hot instruments. With the advent

of this instrument, gutta percha is thermoplastesized in a specially designed

gun that is connected to an electronically controlled unit (see Fig. 1E).

Varying tip sizes determine the depth of penetration (ie, the thinner the tip,

the deeper the penetration). In this manner, the canal is more homoge-

neously and densely filled. The use of the compactor is especially useful

when dealing with internally resorbed canals that cannot properly be filled,

even with the lateral condensation technique.

Nickeltitanium files

The nickeltitanium (NiTi) revolution took place in the mid-1990s. Now

there are numerous NiTi rotary file systems available (see Fig. 1B). At

the time of this writing, there are over 20 different types of NiTi rotary

file systems available, with new ones being introduced every year. This

development is similar to the titanium implant development some years ago.

In 1980, there was only one system; now there are so many. One salient



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question is, Will NiTi file systems replace the stainless steel K-file system?

The answer is definitely not. The NiTi file systems are very convenient for

milling the canal but not for cutting the canal dentin. Cutting the dentin isusually done with GatesGlidden burs or K files in combination with NiTi

rotary files. By using these instruments, the canals can be prepared more

easily and uniformly. Some clinicians avoid the NiTi rotary systems due to

breakage of the file tip inside of the canal. This breakage can be minimized

greatly by light-handed and careful use. The author considers the NiTi file

system not a must-have instrument, but rather a convenient instrument.

There are basically two types of NiTi systems: the LightSpeed (Light-

Speed, San Antonio, Texas) and the non-LightSpeed types. The LightSpeed

type is a miniaturization of the GatesGlidden bur, with a 0.02-type handlewith varying file tip diameters. The non-LightSpeed types include active

systems with a positive rake angle that cut the dentin, and others that are

passive with a negative rake angle that mill the dentin. For instance, the

most popular type is the ProFile (Dentsply, Tulsa, Oklahoma) with a

negative rake angle. Each of these systems offers files ranging from 0.02 to

0.12 taper with smaller tip diameters.

Although there are many pitfalls on the road to consistent results, with

proper use of the NiTi systems, endodontists will be able to improve the

quality and esthetics of their endodontic obturations quickly.

Mineral trioxide aggregate

Mineral trioxide aggregate (MTA) is a reliable new endodontic material

initially designed as a retrofilling material. More recently, it also has been

advocated for pulp capping, perforation repair, and even as an endodontic

filling material for apexification. MTA is a mixture of many oxides and looks

like grayish-brown sand. In fact, it handles like sand and some clinicians have

compared it to Portland Cement. In a moist environment, it sets in about 7hours. In conventional endodontics, it has proved to be the best material for

most types of perforation. Its unique physical property is its compatibility

with bone. It has been shown in numerous studies and in clinical practice that

it is the only material into which bone and cementum cells actually grow,

thereby creating a perfect seal and an ideal barrier. This is a material that has

long been on the endodontic wish list because perforations during endo-

dontic procedures or during post preparation are not that uncommon.

Anatomy of modern endodontic practice

Excellent and consistent endodontic outcomes are still very difficult to

obtain. With the incorporation of the new generation instruments, along

with a thorough knowledge of the root canal anatomy and endodontic

practice, however, far better and more consistent results can be obtained



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than in the past. To illustrate the modern endodontic procedural sequence

of a normal case of a maxillary first molar, an itemized sequence follows:

1. The diagnosis indicates that endodontic treatment is needed and the

tooth is anesthetized.

2. Following placement of the rubber dam, access is made. The microscope

is not needed for this step, although some clinicians may prefer to use it.

3. Using the microscope at low to mid magnification, the pulp chamber isthoroughly prepared using a Buc tip size 2 for inspection.

4. Under high magnification (1624), the floor of the chamber is

examined for additional canals because more than 50% of molar teeth

have a fourth canal (Fig. 5).

5. After the canal entrance is identified, the microscope is not needed until

a later stage. The apex is negotiated with a size 10 K file and is then

enlarged with size 15 or 20 files.

6. GatesGlidden burs are used in reverse order to enlarge the coronal one

half or two thirds using the crown down technique. During this enlarge-ment, it is important to use irrigants (2.5%5% sodium hypochlorite and

17% EDTA solution) to penetrate deep into the canals.

7. An apex locator is used to determine the canal length at this stage. In

this manner, a more accurate canal length measurement is possible

because coronal interference has been eliminated.

8. NiTi rotary instruments are now employed to prepare the remaining one

half or one third of the apical canal in the crown down manner. The

final apical preparation or determination of the master apical file is done

by hand instruments or LightSpeed, depending on the original canalwidth or estimate of working width.

9. The microscope is used to check the preparation and to check again for

an additional canal or canals (the author has found up to six canals in

molars)(Fig. 6).

10. A master gutta percha cone is selected; the canal length and solid tug

back is assured.

Fig. 5. At high magnification, a fourth canal (MB2) of a maxillary first molar can easily be

detected (A) and is shown with a size 10 file in the canal entrance (B). (Courtesy of F. Maggiore,

DDS, Rome, Italy.)



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11. This master cone, coated with root canal cement, is inserted into the

canal, and the coronal part of the point is seared off using System B. The

gutta percha in the apical 3 to 4 mm is packed with S-Kondensers.

12. The Obtura gutta percha compactor with an appropriate tip is inserted

into the canal up to where the master gutta percha was seared off. The

thermoplastesized gutta percha fills the canal as the tip is slowly

withdrawn.13. The microsocpe is used again for a final check. Finally, the canal is

sealed with temporary cement.

This brief sequence shows the use of modern endodontic instruments.

The purpose of incorporating these advanced instruments is to perform

endodontic procedures more accurately, thus experiencing less postopera-

tive discomfort, fewer procedural errors, and a more efficient procedure.

Although the ultimate criteria (ie, whether the incorporation of these

Fig. 6. Radiograph of the maxillary first molar prior to endodontic therapy (A) and micro-

scopic examination of the prepared four canals at 24 magnification of the same tooth (B).

Fig. 7. Multicanal cases done by endodontic graduate students at the University of

Pennsylvania using the modern instruments and techniques described in this article.



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instruments provides greater treatment results and success) has still not been

established in a formal study, the authors clinical experience of the last 10

years has shown that the procedures are more predictable, efficient, andreliable, and result in fewer flare-ups and less discomfort for patients. In

addition, the radiographic results are far better, with a significant increase of

over 40% in locating fourth canals in molars (Fig. 7). These improvements

are truly significant.



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The microscope and endodontics

Syngcuk Kim, DDS, MPhil, PhD, MD(hon)a,*,Seungho Baek, DDS, PhDb

aDepartment of Endodontics, School of Dental Medicine, University of Pennsylvania,

240 South 40th Street, Philadelphia, PA 19104-6030, USAbDepartment of Conservative Dentistry, Seoul National University, Seoul, Korea

It may seem surprising that the microscope is not a high-tech instrument.

It has been used in the medical field for over 50 years. According to the Zeiss

Company, the microscope was first introduced to otolaryngology around

1950, then to neurosurgery in the 1960s, and to endodontics in the early

1990s. Dentistry, therefore, is about 40 years behind medicine in this respect.

As in medicine, the incorporation of the microscope in clinical endodontics

has had profound effects on the way endodontics is done and has changedthe field fundamentally. For this reason, the 1998 American Dental Asso-

ciation accreditation requirement change states that all accredited United

States postgraduate programs must teach the use of the microscope in non-

surgical and surgical endodontics. This was a giant step forward in the

advancement of endodontics.

This article outlines the key prerequisites for the use of the microscope in

nonsurgical endodontic procedures. There are many microscopes on the

market; the three most popular ones are presented inFig. 1.

Prerequisites for the use of the microscope in nonsurgical endodontics

Rubber dam placement

The placement of a rubber dam prior to any endodontic procedure is an

absolute requirement for sterility purposes. This technique is taught at all

dental schools. In endodontics, however, the purpose is greater. Here, the

rubber dam placement is necessary because direct viewing through the canal

with the microscope is difficult, if not impossible. A mirror is needed to reflect

the canal view that is illuminated by the focused light and magnified by the lens

of the microscope. If the mirror were used for this purpose without a rubber

* Corresponding author.



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dam, then the mirror would fog immediately from the exhalation of the

patient. Thus, the powerful microscope magnification and illumination wouldbe rendered totally useless for the necessary visualization of the chamber floor

and the canal anatomy. To absorb reflected bright light and to accentuate the

tooth structure, it is recommended to use blue or green rubber dams (Fig. 2).

Fig. 1. The three most popular microscopes in endodontics.

Fig. 2. The use of a rubber dam is essential for effective microscope use.

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Indirect view and patient head position

As mentioned previously, it is nearly impossible to view the pulp

chamber directly under the microscope. Instead, the view seen through the

microscope lens is a view reflected by way of a mirror. To maximize

the access and quality of the view by this indirect means, the position of the

patient (especially the head position) is important (Fig. 3). The optimum

angle between the microscope and the mirror is 45, and the clinician should

be able to obtain this angle without requiring the patient to assume an

uncomfortable position. The maxillary arch is rather easy for indirect

viewing. Basically, the patients head is adjusted to create a 90 angle

between the maxillary arch and the binocular (Fig. 4). In this position, the

mirror placement will be close to 45 for best viewing.

Mouth mirror placement

It is always a good idea to use the best mirror for this purpose. If a rubber

dam has been placed, then the mirror must be placed away from the tooth

within the confines of the rubber dam. If the mirror is placed close to the

tooth, then it will be difficult to use other endodontic instruments. Read-

justing the mirror will necessitate refocusing of the microscope, making the

entire operation time-consuming and, at times, frustrating. This is especiallytrue during a lengthy perforation repair. With practice, however, the

correct placement of the mirror will become automatic.

Some key instruments

The ability to locate hidden canals is the most important and significant

benefit gained from using the microscope. To do this effectively and efficiently,

clinicians must use specially designed microinstruments. An explorer can pick

the entrance of a canal under the microscope, but negotiating the canal with

Fig. 3. Patients should wear protective dark glasses and have support for the neck, such as

a moldable pillow.

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a file can be challenging because there is only a tiny space between the mirror

and the tooth for a finger with a file to move around. Files specially designedby Maileffer, called microopeners, have with different sized tips and can be

extremely useful (Fig. 5). These hand-held files allow the clinician to initially

negotiate the canal, verifying that the catch is truly a canal. After the canal

is located in this manner, clinicians can instrument the canal normally without

the microscope. The use of GatesGlidden burs to enlarge the canal entrance

prior to full instrumentation, however, can be easily achieved under the

microscope, facilitating the subsequent steps of canal instrumentation.

Fig. 4. Positioning the microscope. Notice the ergonomics of the clinician and comfortable

patient position.

Fig. 5. Micro-openers by Maillefer are ideal instruments for exploration of hidden canals at

high magnification.



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For what procedures is the microscope really essential?

Some enthusiasts claim that the microscope must be used for all steps of

nonsurgical endodontic procedures. This may a noble idea, but in reality, it

is not needed or desired. A clinician must consider the benefit/risk ratio

when using the microscope. The following procedures are those that benefit

from the use of the microscope.

Diagnosis

The microscope is an excellent instrument to detect microfractures

that cannot be seen by the naked eye or by loupes. Under 16 to 24

magnification and focused light, any microfracture can be easily detected(Fig. 6). Methylene blue staining of the microfracture area assists this effort

greatly.

A persistently painful tooth after endodontic therapy may be due to an

untreated missing canal (eg, MB2 in a maxillary molar). Re-examination of

the chamber at high magnification under the microscope may locate the

missing canal (see the article by Kim elsewhere in this issue [Fig. 5]). It has

been the authors experience at the University of Pennsylvania Graduate

Endodontic Clinic that the main cause of a symptomatic tooth following

radiographically satisfactory endodontic therapy is an untreated canal.

Locating hidden canals

As discussed in many sections in this issue, the most important utility of

the microscope in nonsurgical endodontics is locating hidden canals. The

canal anatomy is extremely complex. All endodontic textbooks have

information on molar teeth with three canals, premolars with two canals,

and anterior teeth with one canal. Often, dental anatomy is not that

predictable. Following the introduction of the microscope to the GraduateEndodontic Program at the University of Pennsylvania in 1992, it has been

Fig. 6. Microfracture detected under the microscope (A) and the same tooth after extraction

(B). Arrows identify the fracture line.



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found that nearly an astounding 50% of all molars (maxillary and

mandibular) have a fourth canal, more than 30% of all premolars have

a third canal, and close to 25% of all anterior teeth have two canals. Whatwas considered a rare exception in the past has become a routine finding

when using the microscope. Considering this as the benefit of using the

microscope for endodontic procedures is obvious.

There are teeth where the canal bifurcates at 3 to 5 mm into the canal and

in the maxillary second molar, where the MB and DB are in very close

proximity of each other; the microscope is an invaluable tool in clearly

detecting the bifurcation and the two separate canals.

Management of calcified canals

With normal vision or low-power loupes, calcified canal in the pulp

chamber is not detectable. When the calcified canal is looked at through the

microscope at high magnification, however, the difference in the color and

texture between the calcified canal and the remaining dentin can be easily seen.

Careful probing and ultrasonication using CPR or Buc tips (Obtura/Spartan,

Fenton, Missouri) will allow clinicians to detect and negotiate the calcified

canal easily (Fig. 7). Sometimes in these cases, the ultrasonic preparation of

the canal or canals has to go as far as a couple of millimeters short of the apex.Again, the microscope allows the clinician to detect and prepare conserva-

tively, and not to gouge the healthy dentin structures (Fig. 8).

Perforation repair

Perforation does occasionally occur no matter how carefully the tooth is

accessed for endodontic therapy. When a perforation occurs, the microscope

is the key instrument to identify and evaluate the damaged site. The results

of a careful inspection will be the basis for which the preparation of the

Fig. 7. Buc tips (Obtura/Spartan) are ideal ultrasonic instruments for cleaning the pulp

chamber and floor for clear viewing of the canals.



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perforation repair will be made (see the article by Kratchman elsewhere inthis issue). Briefly, the microscopic procedure is to place a matrix precisely,

just outside of the perforation site (ie, just exterior of the root substance).

The matrix can be calcium sulfate or resorbable collagen. After the matrix is

placed, mineral trioxide aggregate is packed against the matrix. This

procedure requires delicate and careful handling of the materials so as not to

extrude, overfill, or underfill. The microscope is essential for this procedure.

Retrieval of broken files

With the more frequent use of nickel-titanium rotary files in generaldentistry, the incidence of file separation within the canals has increased.

When the file is broken at the apex, the microscope cannot be of help. If

the file breaks within the coronal half of the canal, however, then the

microscope is essential to guide the clinician to retrieve the broken files. In

this manner, the broken file can be removed while minimizing the damage to

the surrounding dentin.

Final examination of the canal preparation

It takes a simple step to see whether a canal is completely cleaned. Under

the microscope, a small amount of sodium hypochlorite, a popular irri-

gation solution, is deposited into the canal and observed carefully at high

magnification. If there are bubbles coming from the prepared canal, then

there is still remnant pulp tissue in the canal. In short, the canal needs more

cleaning.

Fig. 8. Access preparation and management of calcified canals at a high magnification under

the microscope (AF). (Courtesy of F. Maggiore, DDS, Rome, Italy)



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Cost versus patient benefit

Many of the practitioners who perform endodontic procedures and do

not yet own a dental microscope are still evaluating the benefits of its use.

Practicality is the key concern. How does one recoup the cost of the capital

expenditure and the cost and time associated with training? Are the clinical

benefits worth the expenditure of time and money?

To address the critical cost and efficiency issue, clinicians should take an

intensive training course at the very beginning to make them comfortable

with handling the microscope and with working underneath it. Clinicians

should also become totally committed to using the microscope in each of

their treatment cases, not just selected ones. This practice is the fastest route

toward proficiency and the best way to maximize the return on investment.

In addition to clinical benefits associated with the use of the microscope

in endodontics, after the initial learning curve, endodontic procedures

can be done in less time because of the greater visibility of the root canal

anatomy. Procedural errors can be greatly reduced, if not eliminated, and

complicated cases become less so under the microscope.

Another benefit of the microscope is the flexibility with documentation.

Compared with intraoral video cameras, microdental images can be

captured on computer or digital camera. The information can then be

shared with referring dentists or patients and the images are, of course, also

required information for the patient record.



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Nonsurgical ultrasonic

endodontic instruments

Mian K. Iqbal, BDS, DMD, MSDepartment of Endodontics, The Robert Schattner Center, University of Pennsylvania,

School of Dental Medicine, 240 South 40th Street, Philadelphia, PA 19104-6030, USA

One of the most important advancements in endodontics has been the use

of the surgical operating microscope, which in turn necessitated the

evolution of a number of microendodontic instruments. Among these,

ultrasonic instruments have improved the most. Ultrasonic technology has

been available for a long time[1]; the only thing needed to make a modern-

day ultrasonic instrument was incorporation of a contra-angle bend and

parallel working ends. The contra-angle design allowed for dramaticimprovement in procedural access for both anterior and posterior teeth,

in addition to an unobtrusive view under the microscope.

Ultrasonic instruments play an ever-increasing role in several aspects of

endodontic treatment. Teeth with root canal obstructions are no longer au-

tomatically treatment planned for surgical endodontics; endodontic retreat-

ment has become the procedure of choice. In addition, root canal obstructions

are being removed in a more conservative manner that does not unnecessarily

destroy the root structure. The identification of missed and hidden canals has

become a predictable outcome rather than a serendipitous discovery. Accesscavities are being cut and refined with greater precision, opening up gateways

to better endodontics. Above all, these procedures are no longer being

performed blindly; instead the clinician is now able to maintain visual contact

with the operating field at all times during ultrasonic procedures.

The ultrasonic technique is essentially a nonrotary method of cutting

dental hard tissue and restorative materials using piezo-electric oscillations.

Cutting dentine structure with ultrasonic tips is analogous to cutting dentine

with the thinnest bur imaginable. Because the operating field is so restricted,

the use of high magnification and proper illumination is essential during theuse of these instruments. The combination of ultrasonic instruments with the



doi:10.1016/j.cden.2003.10.001

Dent Clin N Am 48 (2004) 1934


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magnification and illumination provided by surgical operating microscope

has been termed microultrasonics.

A variety of ultrasonic tip designs are available, varying in complexityfrom simple curves to multiangled bends. These tips can be long and slender

or short and sturdy; they also can be end cutting or side cutting, and made

of different materials such as stainless steel or titanium alloys. Stainless steel

tips may be coated with zirconium nitride or diamond grit to increase

efficiency and durability. Some tips are designed to function dry, whereas

others come with water ports to increase the cooling and washing effect. A

thorough understanding of these and other variables is critical for the

proper selection and usage of ultrasonic tips.

Almost all of the currently available systems provide the option for usingultrasonic instruments in a wet or dry field. The advantages of a wet field

include easier washing of the field and the cooling effect. However, the area

must be dried to provide the clinician with a clearer view of the operating

field. A Stropko surgical irrigator (EIE/Analytic Technology, Orange,

California) may be used to work continuously in a dry field. The device

attaches to a standard quick-change airwater syringe and can be used to

blow air on the field to maintain visibility. This allows the clinician to

maintain visual contact with the operating field at all times during the

procedure. The irrigator not only delivers a controlled stream of water andair to precisely irrigate and dry the operative field, but also prevents the

development of localized emphysema.

Today, ultrasonic tips are being made and coated with different

materials. The Enac ultrasonic endodontic system (Osada Electric Co.,

Tokyo, Japan) uses stainless steel tips that are effective and very economical

(Fig. 1). To improve efficiency, ultrasonic instruments also have been

manufactured with a coating of zirconium nitride (ProUltra ultrasonic

instruments; Dentsply, Tulsa, Oklahoma). These tips are designed to

function dry. CPR ultrasonic instruments (Spartan CPR instruments,Fenton, Missouri) are similar in design to the ProUltra instruments, except

that they are diamond coated and have built-in water ports (Fig. 2). These

instruments are designed primarily to function on Spartan Piezo-Electric

units (Obtura/Spartan, Fenton, Missouri). Diamond-coated tips purport-

edly last longer and are associated with greater efficiency when compared to

uncoated or zirconium nitride-coated tips. Both the CPR and ProUltra

systems also are accompanied by a set of slender and long tips made from

titanium alloys (Fig. 3). Titanium alloy provides flexibility and greater

vibratory motion to the tips. These tips are end cutting and are employed forcutting deep inside the root canals. Recently, a set of BUC (Fig. 4) access

refinement tips (Spartan instruments) have been introduced to the market.

The BUC tips also are diamond coated and have built-in waters ports that

constantly bath the activated tips. The 4 series (Sybron Endo, West

Collins Orange, California) is another popular system that is geared for

troughing around posts and opening calcified canals (Fig. 5).

20 M.K. Iqbal / Dent Clin N Am 48 (2004) 1934


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Breakage of ultrasonic tips is a common phenomenon. Once broken, these

tips usually jump out of the canal or can be retrieved easily. However, some

of these tips are quite expensive and must be used properly to avoid

unnecessary breakage. The most common reason that tips break is because

Fig. 1. Two tips from the Osada Enac ultrasonic endodontic system. The ST21, shown at the top,

is used for removing solids from root canals. The bottom picture shows the vibratory tip ST09.

Fig. 2. Retreatment CPR tips 2D through 5D are diamond coated with built-in water ports that

allow for wet or dry cutting.

21M.K. Iqbal / Dent Clin N Am 48 (2004) 1934


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they are not operated at their recommended frequencies. Therefore, it is

important to follow the manufacturers recommendations with regard to the

ultrasonic intensity at which a particular tip must be used. The results of

a recent study [2] revealed a significant increase in displacement amplitude

Fig. 3. Titanium CPR ultrasonic tips 6 through 8.

Fig. 4. BUC access refinement tips 1 through 3.



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and depth of dentine cut with an increase in power setting. However, the

slender and longer tips with small cross-sectional diameters (ie, CPR 68) will

fracture easily when used at high intensity. On the other hand, short and

sturdy tips used for vibrating posts out of root canals are operated at

medium-high intensity. Similarly, tips that are used for bulk removal of

dentine or restorative materials (eg, CPR 2) also need to be used at moderate

to high intensities. The troughing tips (eg, CPR 3D5D, BUC 3, and CPR 68) should be used at low intensity. In general, thick and short tips are

operated at higher intensities, whereas long and slender tips are operated at

lower intensities.

Tips with bends increase access to different parts of the mouth; however,

excessive angulations also make these tips more vulnerable to breakage[3].

In addition, tips that are designed primarily for cutting dentine can break

Fig. 5. The 4 series is specially geared toward post removal.



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easily if inadvertently brought into contact with metals. The shanks of

ultrasonic instruments come in different lengths ranging from 15 mm to 27

mm. The instruments are selected according to the depth at which they willbe required to operate inside the root canal. For greater control, the shortest

tip possible to reach the desired depth should be used. Not doing so may

cause breakage of the instruments.

Each instrument system usually comes with its own ultrasonic engine,

which is capable of generating ultrasonic frequencies in the range 20 kHz to

30 kHz. These frequencies generate comparable patterns of oscillation at the

tip of the instruments. However, oscillation of the ultrasonic tip may be

stalled if it is introduced into narrow canals or forcefully applied against

dentine or restorative material. To be effective, these instruments must bekept moving at all times. If the instrument begins to stall, contact with the

cutting surface should be broken temporarily to allow the tip to regain its

oscillations. Also, to experience the full range of power, a wrench should be

used to tighten the instruments in place; otherwise, the instrument may

loosen during use. At the present time, the use of these instruments in

patients with cardiac pacemakers is not recommended.

Although a number of other systems are available, it is not possible to

describe all of them in this article. However, a closer look at the different

systems reveals a number of similarities. From a practical point of view, itbecomes more beneficial to know the utility of each type of ultrasonic tip

rather than the system as a whole. These instruments can be separated into

two categoriesarea specific or use specificand come with established

guidelines; however, it is possible to use an ultrasonic tip in an area other

than the one for which it is specifically designed if the general principles

regarding ultrasonic tips are understood and applied. With this in mind, the

components of the different ultrasonic systems have been broadly classified

as follows: (1) access refinement tips, (2) vibratory tips, (3) bulk removal

tips, and (4) troughing tips.

Access refinement tips

Access cavity preparation is the most important phase of endodontic

therapy. A properly designed access cavity that provides direct line access to

all the root canals is key to endodontic success. A properly designed access

cavity should allow for placement of endodontic instruments in the root

canals in the same manner as flowers are placed in a vase. Traditionally,

access cavities have been refined with burs that were designed primarily foroperative preparations. Recently, a combination of access refinement

ultrasonic tips and magnification has revolutionized the basic concept of

access cavity preparation.

There are many advantages to using ultrasonic tips rather than burs to

refine the access cavity to locate the underlying anatomy. There is no

handpiece head to obscure vision and, therefore, the progressive cutting



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action can be observed directly and continuously under the microscope. The

size of ultrasonic tips is smaller than the smallest burs; therefore, the dentine

can be brushed off in smaller increments and with greater control. Theprocess allows for exposure of any missed or hidden canals or recesses

containing necrotic pulp tissue without gutting down the tooth structure

(Fig. 6). The process is similar to archeologists unearthing artifacts at

excavation sites. The dentine must be brushed off in smaller increments until

the road map on the floor of the pulp chamber is uncovered completely. The

usual term used for this procedure is unroofing the pulp chamber;

however, this term is valid only when dealing with young and large pulp

chambers. For pulp chambers that have receded with calcification, the term

uncovering the floor of the pulp chamber is more appropriate.Another advantage of ultrasonic instruments over burs is the production of

cavitation within the cooling water that flows over the tip of the ultrasonic

instrument [4]. Cavitation may be described simply as bubble activity in

a liquid, which is capable of generating enough shock waves to cause

disruption of remnants of necrotic pulp tissue and any calcific deposits.

Therefore, it is no wonder that access cavities prepared with ultrasonic

instruments have a thoroughly washed out and clean appearance (see Fig. 6B).

A number of tips are available to refine the access cavity. The uncover-

ing of the floor of the pulp chamber can be accomplished with the help ofthe CPR 2D or BUC 1 tips. If the dark, colored floor of the pulp chamber is

not visible, it usually is obscured by pulp stones or tertiary dentine deposits

(Fig. 7). The pulp stones sometimes can be vibrated or teased out by the

CPR 2D or BUC 1 tips (seeFig. 7A); at other times, they can be planed with

the help of a BUC 2 tipa process similar to planing the root surface. The

tip of this instrument is designed with a planed surface and it can grind the

floor until the dark-colored dentine becomes visible. The unveiling of

the dark-colored floor of the pulp chamber is of critical importance because

it dictates and guides the extension of access cavity.

Fig. 6. (A) Mandibular molar requiring retreatment shows presence of gutta-percha in two

mesial and one distal canal. The remaining chamber contained remnants of sealer cement and

necrotic tissue. (B) Removal of gutta-percha filling and use of ultrasonic instruments exhibits

debridement of the chamber and the presence of an untreated fourth distal canal.



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The second mesiobuccal canal (MB2) is reported to occur in more than

90% of maxillary molars[5]. On average, it is located 1.8 mm away from the

mesiobuccal canal in a palatomesial direction. A protocol involving

deepening of the bucco-lingual groove overlying the mesiobuccal root isessential for locating the MB2 [6]. The groove should not be extended

toward the palatal canal but rather in a direction slightly mesial to it, so as

to follow the bucco-lingual orientation of the mesiobuccal root. The refining

tips can accomplish this task in a much-controlled manner by deepening the

groove while at the same time restricting its mesiodistal dimension so as to

not perforate the furcal or mesial aspect of the tooth.

The refining tips also are used for moving the mesial marginal ridges

mesially to have a direct line access to the MB2 canal [7]. In addition, the

tips also can be used for delineating the outlines of the root canal orifices sothat the overhanging dentine deposits are removed and the orifices are

exposed. This step sometimes can reveal the presence of two canals in

a single orifice and helps to guide the instruments easily in and out of the

canals. The ultrasonic tips can be used to dig and follow the sclerosed canals

until patency is achieved. However, this procedure must be accomplished by

a number of radiographic checks and restricted to the coronal aspect of the

Fig. 7. (A) An ultrasonic tip is being used to remove heavy calcific deposits on the floor of

a maxillary molar pulp chamber. (B) The use of ultrasonic energy led to shattering of pulp

stone. (C) This picture reveals the presence of four root canal orifices, but the absence of any

pulpal floor road map. (D ) Continued removal of calcification and refinement of access cavity

with ultrasonic instruments exposes the floor of the pulp chamber and the presence of an

additional distobuccal canal. (Courtesy of Dr. Helmut Walsch, Munich, Germany.)



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root trunk only. To check progress, an ultrasonic tip is used to dig a test

hole at the most probable site of the sclerosed canal. The test site is filled

with thermoplastisized gutta-percha and an orientation radiograph isexposed (Fig. 8). If the test site is found centered in the root and pointing

correctly, then cutting is continued to enter the canal; otherwise, the

direction of the cutting is modified according to information gathered from

the radiograph. Radiographs are two dimensional in nature, however, and

do not provide any information regarding the bucco-lingual depth of the

tooth structure.

Vibratory tipsRemoval of intraradicular posts has always been a challenge when

performing endodontic retreatment. This procedure also has been fraught

with unwanted consequences, such as root fracture or perforation. The

implementation of ultrasonic energy has provided the clinician with an im-

portant adjunctive method for removal of posts. A number of studies[811]

have shown conclusively that the use of ultrasonic vibration significantly

reduces the amount of tensile force required to dislodge both the cast and

prefabricated posts. The VT (Sybron Endo), Osada Enac ST09, and CPR 1

are examples of such instrument tips. The tips of these instruments arespherical or flat and are placed against the post to transmit vibration. They

Fig. 8. A check radiograph of a calcified central incisor showing an ultrasonically prepared test

site filled with radiopaque gutta-percha. The ultrasonic tip was not aligned parallel to the long

axis of the tooth and needed to be redirected to avoid root perforation.



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are activated at the maximum intensity and moved circumferentially until

the post loosens or dislodges. If this method does not loosen and free the

post then alternate methods must be used. The manufacturer cautionsagainst placing these tips directly on ceramics because it may cause severe

damage to the prosthesis.

The inability to remove posts by vibration alone is dependent on many

factors such as the type of luting agent, the length and type of the post, and

the type of core buildup. The core buildup around the post should be

removed before applying the vibratory tip. In some cases, the troughing tip

should be used around the post and then vibratory tips should be reapplied to

obtain the maximum benefit. Posts luted with zinc phosphate cement can be

dislodged readily by ultrasonics because of microcrack formation in thecement[12].However, posts luted with resin cements such as Panavia fail to

dislodge by ultrasonic vibration, probably due to the lack of the micro-

fracture propagation in these materials[12].

Bulk removal tips

Bulk removal tips are extremely sharp and sturdy tips that are operated at

moderate or maximum intensity of the ultrasonic unit. BUC 1 and CPR 2D

are examples of tips that fall into this category. Both of these tips are diamondcoated and have an added advantage of a water port placed near the cutting

surface of the tip for increased washing and cooling of the operative site.

These tips are designed primarily to remove dentine and core material

quickly and expeditiously before subjecting the root canal obstruction to

vibratory or troughing procedures. In retreating cast post and cores, the

core portion is reduced and sculpted until it becomes an extension of the

post itself[13]. This gives the clinician a purchase point to apply extraction

devices when normal vibratory motions fail to dislodge the post completely.

The controlled and incremental cutting with ultrasonic instruments undermagnification provides a clear contrast between the core materialsfor

example, between composites and the underlying dentinal structure.

Therefore, the chances of inadvertently perforating the crown of a tooth

are reduced greatly.

Troughing tips

Troughing tips are used to create a sufficiently deep trough around poststo maximize the benefits of subsequently applied vibratory or extraction

forces. In the past, troughing around the root canal obstruction was per-

formed with trephine drills. This process was extremely destructive and fre-

quently led to the gutting down and perforation of root trunks. Now with

the help of ultrasonic tips, troughing around root canal obstructions can be

performed in a predictable and controlled manner.



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Initially, the troughing is performed with instruments such as CPR 3D,

4D, and 5D, which are 15, 20, and 25 mm in length, respectively (Fig. 9).

These instruments are used in the coronal, middle, and apical one third of

root canals and their selection depends on the depth at which they need to

be operated. These instruments are diamond coated and aggressively cut

dentin along their lateral sides. The BUC 3 (Obtura/Spartan, Fenton, Ohio)

or CT 4 tip (Sybron Endo), which also is available with a diamond coating,

can be used for this purpose. The instruments not only remove cement thatmay be present around the post, but also remove a thin shelf of dentine

around the perimeter of an obstruction.

If the obstruction is located in the deeper part of a straight canal, then

titanium CPR tips 6 (red), 7 (blue), and 8 (green) are used, which are 20, 24,

and 27 mm long, respectively. These instruments are quite slender, long, and

parallel sided to cut deep into the root without taking away too much

dentine, and at the same time provide maximum visibility under the

microscope (Fig. 10). These instruments are especially useful when removing

long and thick prefabricated post systems (Fig. 11). The fact that these

Fig. 9. The initial troughing around a post can be performed with shorter tips such as diamond-

coated CPR 2D or 3D. (Courtesy of Dr. Samuel Kratchman, Exton, PA.)

Fig. 10. (A) CPR 6 is being used to trough between the post and the lingual wall of the root

canal. (B) View of the trough produced around the lingual aspect of the post with the help of

ultrasonic files.



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instruments are made of titanium alloys and have thin cross-sectional

diameters makes them extremely flexible and vibrant, but, at the same time,

subject to breakage. The instruments should be used with a light touch; that

is, with the same amount of pressure used to avoid breaking the lead tip of

a pencil. These tips most commonly fracture when inadvertently brought

into contact with metallic objects such as posts. Therefore, extreme caution

needs to be taken when using these instruments. The instruments must beused at low intensities and always under the magnification provided by the

microscope so as to not inadvertently contact any metallic obstruction.

Unlike CPR tips 3D, 4D, and 5D, which are diamond coated and active

along the sides of their tips, CPR tips 6, 7, and 8 are end cutting and only

active at their tips. Therefore, before troughing with these tips a collar of

dentine must be exposed around obstructions that are embedded in root

canals. The collar or shelf of dentine can be prepared around the

obstructions with the help of LightSpeed instruments (LightSpeed, Inc.,

San Antonio, Texas). The tips of these instruments are flattened with thehelp of a grinding stone (Fig. 12), which allows them to cut dentine as close

to the obstruction as possible. The instruments are used sequentially to the

coronal extent of the obstruction until the canal is enlarged sufficiently, and

a shelf of dentine is prepared around the obstruction (Fig. 13). Gates

Glidden (GG) drills also can be used for this purpose; however, GG drills

can be used only in the straight portions of the canal and are unable to

Fig. 11. (A) Radiograph showing the presence of a long, threaded post associated with a failing

root canal treatment. (B) Radiograph showing completion of root canal treatment afterremoval of the threaded post.



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negotiate any curvatures in the root canals [13]. Nevertheless, retreatment

becomes difficult when the coronal end of the instrument lies apical to the

elbow of the curvature and cannot be seen with the help of the surgical

operating microscope. Once the shelf of dentine is prepared, CPR tips 6, 7,

and 8 can be used to create a trough around the instrument (see Fig. 13D).

The tips are moved counterclockwise around the fractured instrument todisengage it from the surrounding dentine [14]. Once loosened, the

instrument usually moves coronally and jumps out from the root canal

(Fig. 14). In other instances, the exposed part of the separated instrument

can be grabbed and pulled out with one of the currently available extraction

devices.

The use of NiTi rotary instruments has increased the incidence of file

separation in endodontics. The NiTi files mainly break by either torsional

fracture or flexural fatigue [15]. In the former case, the instrument usually

gets forced into the root canal and, once jammed, fractures at its weakestpoint. This type of failure is associated most often with an unwinding of

flutes that can be recognized under the operating microscope (Fig. 15A).

The fractured instruments usually are engaged into dentine along their

whole lengths and at times may be difficult to remove. On the other hand,

fatigue failure causes the instrument to fracture at the point of its maximum

flexure. These instruments do not exhibit any unwinding of flutes when

observed under the operating microscope (seeFig. 15B). Even though these

instruments are not tightly bound in dentine, they may be difficult to access

because their coronal ends usually are located apical to the elbow of rootcurvature.

In addition to trephining around posts and removal of broken instru-

ments and other intracanal obstructions, ultrasonic instrumentation also

can be used for eliminating brick-hard paste-type materials [16]. The

procedure can be accomplished with CPR 3D, 4D, and 5D; BUC 3; or ST21

Enac tips under the microscope so that the paste can be differentiated easily

Fig. 12. Drawing showing LightSpeed instruments flattened at their tips with the help of

a grinding stone.



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Fig. 13. (A) Initially, a small-sized instrument is selected and carried down to the obstruction.

(B) Instruments are used sequentially to enlarge the root canal space. The arrow in the figure

points toward the approximation of a modified LightSpeed instrument and the root canal

obstruction. (C) The arrow in the figure points toward a shelf of dentine that has been created

around the separated instrument. (D ) The arrow indicates a trough created around the

separated instrument with the help of ultrasonic tips.



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from the surrounding root canal dentine. Under the microscope, the

pastedepending on its colorappears as a white or pinkish dot. The CPR

tips are used to eliminate it by following the dot to its apical extent.

However, no attempt should be made to remove paste materials around

curves, because the ultrasonic files are unable to negotiate curvatures and

may lead to perforation of the root surface. Ultrasonic tips also can be used

to help MTA flow precisely into place. This is done by depositing mineral

Fig. 14. (A) Preoperative radiograph of a maxillary left first premolar shows a separated

instrument in the palatal canal. (B) Postobturation radiograph. The instrument was removedeasily with ultrasonic vibration. (Courtesy of Dr. Bekir Karabucak, Philadelphia, PA.)

Fig. 15. (A) Drawing of a NiTi instrument depicting unwinding of the flutes associated with

a torsional failure. (B) In case of flexure failure, no signs of unwinding of the flutes can be noticed.



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trioxide aggregate (MTA) at a site (ie, perforation) and then vibrating it

with an activated ultrasonic tip until it flows evenly into the defect.

Summary

The use of ultrasonic instruments has revolutionized the art of

endodontic retreatment. These instruments have multiple uses and have

become an integral part of the endodontic armamentarium. However, the

use of ultrasonic instruments requires specialized knowledge and de-

velopment of certain skills that may require training before use.

References

[1] Martin H. Ultrasonic disinfection of the root canal. Oral Surg Oral Med Oral Pathol 1976;

42(1):929.

[2] Waplington M, Lumley PJ, Blunt L. An in vitro investigation into the cutting action

of ultrasonic radicular access preparation instruments. Endod Dent Traumatol 2000;

16(4):15861.

[3] Walmsley AD, Lumley PJ, Johnson WT, Walton RE. Breakage of ultrasonic root-end

preparation tips. J Endod 1996;22:2879.

[4] Roy RA, Ahmed M, Crum LA. Physical mechanisms governing the hydrodynamicresponse of an oscillating ultrasonic file. Int Endod J 1994;27(4):197207.

[5] Kulild JC, Peters DD. Incidence and configuration of canal systems in the mesiobuccal root

of maxillary first and second molars. J Endod 1990;16(7):3117.

[6] Weller RN, Hartwell GR. The impact of improved access and searching techniques on

detection of the mesiolingual canal in maxillary molars. J Endod 1989;15(2):823.

[7] Instructions for use. BUCTM non-surgical ultrasonic endodontic instruments. Fenton

(MO): Spartan Marketing Group. Available at: http://www.obtura.com/bucaccesstips.html.

Accessed on January 21, 2004.

[8] Buoncristiani J, Seto BG, Caputo AA. Evaluation of ultrasonic and sonic instruments for

intraradicular post removal. J Endod 1994;20:4869.

[9] Berbert A, Filho MT, Ueno AH, Bramante CM, Ishikiriama A. The influence ofultrasound in removing intraradicular posts. Int Endod J 1995;28:1002.

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Electronic apex locator

Euiseong Kim, DDS, MSD, PhDSeung-Jong Lee, DDS, MS*

Department of Conservative Dentistry, School of Dentistry, Yonsei University,

134 Shinchon-dong, Seodaemun-gu, Seoul 120-752, Korea

Locating the appropriate apical position always has been a challenge in

clinical endodontics. The cemento-dentinal junction (CDJ), where the pulp

tissue changes into the apical tissue, is the most ideal physiologic apical limit

of the working length. It also is referred to as the minor diameter or the

apical constricture. However, the CDJ and apical constricture do not always

coincide, particularly in senile teeth as a result of cementum deposition,

which alters the position of the minor diameter. Therefore, setting the apical

constricture as the apical limit of the working length, where it is easy to

clean and shape or obturate the canal, is recommended [1,2].

The apical constricture of the root also does not coincide with the

anatomic apex. It is deviated linguo-buccally or mesio-distally from the root

[35]. If the exit deviates bucco-lingually, it is very difficult to locate

accurately the position of the apical foramen using only roentgenograms,

even with multidirected angles. Frequently, a file needs to be inserted into the

canal to force it through the apical foramen, in order for the exit to be verified.

The electronic apex locator (EAL) machine has attracted a great deal of

attention because it operates on the basis of the electrical impedance rather

than by a visual inspection. The EAL is one of the breakthroughs that

brought electronic science into the traditionally empirical endodontic

practice. EALs are particularly useful when the apical portion of the canal

system is obscured by certain anatomic structures, such as impacted teeth,

tori, the zygomatic arch, excessive bone density, overlapping roots, or

shallow palatal vaults. Indeed, EALs currently are being used to determine

the working length as an important adjunct to radiography. EALs help

to reduce the treatment time and the radiation dose, which may be

higher with conventional radiographic measurements. In addition, EALs

* Corresponding author.

E-mail address:[email protected](S-J. Lee).


doi:10.1016/j.cden.2003.10.005

Dent Clin N Am 48 (2004) 3554


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were reported to be an accurate and reproducible method as the newest third-

generation type and can acknowledge a root perforation. However, some

questions still exist as to whether the accuracy of EAL can be affected by thedifferent types of electrolytes [19,43,45], the types of electronic working

mechanism, and the conditions of the root canal, such as pulp vitality

[20,31,34], or foramen size [51,52]. This article reviews the history and the

working mechanism of the currently available EALs, and suggests the correct

use of an apex locator for a better canal length measurement.

History of EALs

Traditional-type apex locators (resistance or impedance type)

In 1918, Cluster[6]first put forth the idea that the root canal length could

be determined by using the electrical conductance. Little was done with this

idea until 1942 when Suzuki [7] reported a device that measured the

electrical resistance between the periodontal ligament and the oral mucosa.

He discovered that in dogs, the electrical resistance between the root canal

instrument inserted into a root canal and an electrode applied to the oral

mucous membrane registered a consistent value of approximately 6.5 Kx.

These principles were not examined further until Sunada [8] performeda series of experiments on patients and reported that the electrical resistance

between the mucous membrane and the periodontium was consistent,

regardless of the age of the patients or the shape and type of the teeth. In

1987, Huang[9]reported that this principle is not a biologic characteristic,

but rather a physical principle.

Inoue [10] reported a modification that incorporated the use of an

audiometric component that permitted the device to relate the canal depths

to the operator via low-frequency audible sounds. One of the most widely

used apex locators in the 1970s and 1980s, the Sono-Explorer (UnionBroach, New York, New York), was developed using this modification. By

1975, newer units such as the Neosono (Amadent, Cherry Hill, New Jersey)

and many other resistance-type apex locators became available. They have

improved circuitry, are more compact, and are easier to operate [11].

However, these resistance-type EALs often yield inaccurate results when

electrolytes, excessive moisture, vital pulp tissue, exudates, or excessive

hemorrhage are present in the canals [1214]. (The effect of the canal

contents on the accuracy of an EAL is discussed later in this article.)

A new apex locator, the impedance type, was developed in the late 1980s toimprove the resistance-type apex locators. The impedance-type EAL uses the

electronic mechanism that the highest impedance is at the apical constricture,

which is the narrowest portion of the canal where the impedance changes

drastically, when a canal is thought of as being a long hollow tube [15].

However, a question also was raised as to whether this mechanism could be

applied to the real root canal with various anatomical complications [16].

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The Endocator (Hygienic Corporation, Akron, Ohio) was an example of

an impedance-type apex locator. This device used a large file coated with

Teflon, which was difficult to use in narrow canals; in addition the Teflonpeeled off in curved canals. Another disadvantage with this device was that

the patient sometimes felt uncomfortable due to the high current used, and

the calibration had to be done before using the device [17].

Frequency-dependent apex locators

The newest type of EAL was introduced in the early 1990s in an effort to

obtain a more accurate canal length measurement in various canal

circumstances. It uses more advanced technology and measures theimpedance difference between the two frequencies or the ratio of two

electrical impedances. In 1990, Yamashita [18] reported on a device that

calculated the difference between two impedances from two different

frequencies, which were generated with composite sine wave current sources,

and was marketed as the Endex (Osada Electric Co., Tokyo, Japan). It

works by comparing the difference in impedances using the relative value of

two alternating currents at frequencies of 1 and 5 kHz. As the file moves

toward the apex, the difference becomes greater and shows the greatest value

at the apical constricture, allowing for a measurement of that location. Themajor advantage of this device is that it works well regardless of the

presence of pus or electroconductive environments in the canal [19,20].

However, a disadvantage is that a calibration needs to be done each time.

In 1991, Kobayashi et al [21] reported on the ratio method for

measuring the root canal length, which was the basic working mechanism of

the Root ZX (J. Morita Corp., Tustin, California)[21]. This device measures

the impedances of 0.4 kHz and 8 kHz at the same time, calculates the quotient

of the impedances, and expresses this quotient in terms of the position of the

file inside the canal. This quotient is barely affected by the electricalconditions inside the canal[14]. In addition, it is unnecessary to calibrate this

device each time because the microprocessor automatically controls the

calculated quotient to have a relationship with the file position and the digital

read out when the file is inserted into the coronal portion of the canal [22].

This device was reported to be quite accurate in various conditions

[2325].

The AFA (all fluids allowed) Apex Finder Model 7005 (Analytic

Endodontics, Orange, California) is another type of frequency-dependent

EAL, which uses five different frequencies (0.5, 1, 2, 4, 8 kHz). The Bingo1020 (Forum Engineering Technologies, Rishon Lezion, Israel) uses two

separate frequencies, 400 Hz and 8 kHz, but only a single frequency at

a time. The use of a single-frequency signal eliminates the need for filters

that separate the different frequencies of the complex signal. In addition, the

position of the file tip in the Bingo 1020 is calculated based on the mea-

surements of the root mean square value of the signal. The manufacturers

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claim that a combination of these two techniques increases the measurement

accuracy[37].

Apex locators with other functions

EALs with additional functions were developed in the late 1990s. The

Solfy ZX (J. Morita Corp.), which is a combination of an ultrasonic hand

piece and a Root ZX, was designed to prevent overinstrumentation by

stopping the ultrasonic vibration when the file reaches the required location.

The Tri Auto ZX (J. Morita Corp.) is a Root ZX with a cordless

rechargeable electric hand piece that uses a Ni-Ti rotary file with 260 to 280

revolutions per minute (rpm) [26]. When the file has reached the required

location, this device allows the file to rotate back out of the canal, thereby

preventing overinstrumentation. In addition, it also prevents the fracture of

the Ni-Ti rotary file by allowing the file to rotate back out if it goes over the

set auto-torque-reverse mechanism threshold of 40 to 80 g/cm [26]. This

unique function appears to be quite useful as the Ni-Ti rotary file becomes

more popular. However, based on our clinical experience, large sized rotary

files had a tendency to slow down the rpm speed, possibly due to the low

torque setting. In addition, it has the disadvantage that the number of rpm

reduces with increasing pressure due to the limitation of the rechargeable

battery.

Recently, the Dentport ZX (J. Morita Corp.) was introduced to the

market. The Dentaport ZX is comprised of two modulesthe Root ZX

module and the Tri Auto ZX module. Both functions can be used by

exchanging the back cover. In the Tri Auto ZX module, it appears that the

file was easily controlled when using the hand piece at 50 to 800 rpm and

a torque ranging from 30 to 500 g/cm. One advantage of the Dentport ZX is

that it has an auto apical slow-down functionwhen the rotary file reaches

the apical constricture, t

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